2 Techno-economic analysis and modeling of carbon dioxide (CO2) capture and storage (CCS) technologies J. O g d e n and N. J o h n s o n, University of California Davis, USA Abstract: This chapter presents an overview of the estimated costs of implementing carbon dioxide (CO2) capture and sequestration (CCS) for fossil energy systems. Cost models for the components of a CCS system are reviewed and developed, including CO2 capture, transport via pipeline and ship, and injection into various reservoirs for storage and/or enhanced fossil fuel recovery. The chapter closes with a discussion of CCS system models and future trends. Key words: carbon capture and sequestration (CCS) economics, CO2 injection, CO2 capture, CO2 transport, CCS system modeling. 2.1 Introduction Implementing carbon capture and sequestration (CCS) on a large scale will involve major investments. Existing fossil energy conversion plants will be retrofitted for carbon capture or replaced with new plants that integrate carbon capture into the process. A new transport infrastructure will be needed to bring carbon dioxide to suitable storage sites, such as underground geological formations. The storage site will include injection wells, piping, and monitoring equipment. In some cases, a new energy delivery system could be required to bring decarbonized energy carriers such as hydrogen to markets. Understanding the design, performance, and costs throughout the whole system is crucial to evaluating the economic viability of fossil energy with CCS, as compared to fossil energy without CCS, and in comparison to other low-carbon energy supply options such as renewables and nuclear power. In this chapter, we review current state of knowledge on technoeconomic modeling of fossil energy systems with CCS. We develop idealized technical and cost models for the entire system and discuss methods and metrics for economic evaluation. A central question for techno-economic studies is how much it will cost to implement CCS for a particular situation. To assess costs and carbon dioxide (CO2) savings with CCS, we need to compare to a reference fossil energy system without CCS. The modeller also needs to specify the system boundaries for the particular analysis, the technology status (e.g., is the 27 © Woodhead Publishing Limited, 2010 28 Developments and innovation in CCS technology system based on current or advanced technology, are costs projected for the nth plant?), economic and feedstock cost assumptions (the engineering/ economic model is embedded in a larger context of energy and policy), and policy constraints such as carbon taxes. These issues are illustrated through a simplified diagram of a ‘generic’ fossil energy system with carbon capture and storage (Fig. 2.1). Most studies consider the total system as three ‘components’, (i) CO2 capture from a source such as a fossil energy plant or industrial complex, (ii) CO 2 transport from the source to a sequestration site, and (iii) the CO2 storage site itself (e.g., an underground deep saline aquifer, a depleted oil field, or a deep unmineable coal formation). We have sketched a fourth ‘component’, the energy demand. Clearly, the characteristics of the demand (the type of energy carriers needed, the scale, location, and time dependence of demand) determine what is required from a fossil energy system with CCS. Moreover, fossil power plants with CCS are part of a larger energy system, which must be considered in economic evaluation of scenarios for CCS deployment. The design of each part of the system depends on a host of factors, some of which are shown in italics. The size and location of the different components of the system depend on regional factors such as the proximity of energy supply to good sequestration sites, and costs depend on local energy prices (for example, the price of natural gas versus coal). System models can be either static or time dependent, generic or geographically specific. Several metrics are commonly used for assessing the economics of fossil energy systems with CCS (IPCC, 2005), relative to a reference case without CCS. First is the capital cost of the system. Second is the levelized cost of energy (for example $/kWh of electricity), which includes the time value of money, and all fixed and variable operating costs. Third is the cost of CO2 in $/tonne of CO2 captured, or $/tCO2 emissions avoided. Various levels of modeling can be used to understand the performance and economics of the whole system. These are loosely grouped as ‘component level engineering/economic models’, ‘system level engineering/economic/ spatial models,’ and ‘macro-economic and integrated assessment models’. Most engineering/economic modeling studies to date focus on one component such as the fossil energy conversion plant, the CO2 transport system or the underground CO2 storage site. Table 2.1 shows the types of inputs and outputs and modeling tools used in component models for different parts of the system. These are described in detail in later sections of this chapter. Some studies combine one or more components into system level engineering/economic/spatial models. Most focus on either the fossil energy complex or the CO2 transport and storage infrastructure (Hendriks, 1994; Ogden, 2003; Herzog, 2006; McCoy, 2008). These models allow sensitivity studies to understand the major costs at the system level. They also enable use of geographic specific data for realistic regional case studies. With © Woodhead Publishing Limited, 2010 Fossil energy complex Fossil feedstock (coal, NG, petroleum, coke, etc.) CO2 transport Distance, geography Energy demand Electricity and fuel energy demands; end-use technologies; geographic layout and time dependence of demand; fuel storage and delivery system Distance, geography CO2 sequestration site Well depth; reservoir characteristics (e.g., permeability, thickness, pressure, temperature, capacity) Recovered oil or gas in the case of EOR, EGR, or ECBM 29 2.1 Fossil energy system with carbon capture and sequestration. Key variables are shown in italics. Techno-economic analysis and modeling © Woodhead Publishing Limited, 2010 Plant design, scale, cost, energy efficiency, and capture efficiency; product mix (e.g., electricity, H2, liquid fuels); pressure, temperature, and purity of CO2 Electricity, H2, liquid fuel transport 30 Developments and innovation in CCS technology Table 2.1 Component level engineering/economic models Fossil energy plant w/CCS (Section 2.2) Inputs: Plant type (post-combustion capture, pre-combustion capture, oxyfuel combustion, capture technology type, new or retrofit); feedstock (coal, natural gas, pet coke, biomass mix); plant capacity; technology status (current or advanced; first plant or nth plant); equipment performance and costs; output product mix (electricity, hydrogen, liquid fuels); CO2 capture rate; plant equipment selection (e.g. type of capture system). Model type: Process simulation for steady-state mass and energy flows (ASPEN, HYSYS); specialized models for particular equipment; equipment cost and performance, models based on existing supplier costs and projections for future technology. Outputs: Plant process flow diagram with mass and energy flows; feedstock and energy inputs, product outputs; plant energy conversion efficiency; rate of CO2 capture; overall plant capital and operating cost as a function of scale; capital cost, cost of carbon capture $/tonne CO2, cost of energy $/kWh electricity or $/GJ fuel. CO2 transport (section 2.3) Inputs: Transport mode (pipeline, ship, truck); CO2 flow rate; CO2 pressure, purity, temperature; distance to sequestration site; pipeline costs per meter of length for various diameters. Model type: Pipeline fluid flow models that find CO2 flow rate as a function of pressure (inlet and outlet), pipeline diameter and length. Cost models based on existing pipeline costs and projections for future technology. Outputs: Pipeline diameter, capital cost, booster compressor requirements, capital and operating cost as a function of scale, levelized cost of transport $/tonne CO 2. CO2 storage (section 2.4) Inputs: CO2 flow rate; CO2 pressure, purity, temperature; sequestration site reservoir characteristics (type of reservoir, pressure, permeability, layer thickness, depth; storage capacity); injection well characteristics (depth, pipe diameter). Model type: Model for diffusion of injected CO2 in porous media. For wells: pipeline fluid flow models that find CO2 flow rate as a function of pressure (inlet and outlet), pipeline diameter and length and well depth. Cost models based on existing CO2 injection well costs and projections for future technology. Outputs: Number of wells, well spacing, piping, and other sequestration site equipment; capital and operating costs for wells and injection site. Levelized cost of storage $/tonne CO2. the increasing availability of geographic information system data, it has become possible to do geographic specific case studies of fossil energy systems with CCS (Herzog, 2006; Johnson and Ogden, 2008; Johnson et al., 2008; Middleton and Bielicki, 2009). Existing CO2 sources and power plant locations, sequestration sites, and potential pipeline locations can be identified for a given region. The model develops an optimized design for CO2 pipelines to connect sources of CO2 and storage sites. Most technoeconomic system models are static, and assume a fixed demand. However, several scenarios for building up regional CCS-based systems over time have been developed (Kuuskraa, 2007; IEA, 2008; Johnson et al., 2008). The costs for making a multi-decade transition to a fossil energy system with CCS can be estimated. © Woodhead Publishing Limited, 2010 Techno-economic analysis and modeling 31 Finally, models of CCS systems have been incorporated into larger models of the energy economy such as MARKAL or NEMS or into integrated assessment models such as MESSAGE. In these models, various energy supply options compete to supply specified demands for energy services such as lighting, cooling, and vehicle miles travelled. These models yield insight into the potential role of fossil energy systems with CCS under different technology assumptions or policy constraints. The next three sections deal with modeling components, as a basis for discussing integrated system models. 2.2 Carbon dioxide (CO2) capture There are a variety of options for capturing CO2 from fossil energy plants. These are classified as post-combustion, oxyfuel combustion, and precombustion decarbonization (Fig. 2.2). Post-combustion capture involves separation of CO2 from combustion flue gases and is appropriate for retrofits to existing fossil energy plants. In oxyfuel combustion, the fuel is burned in pure oxygen, allowing ready capture of CO2. Pre-combustion capture involves a gasification or reforming stage to produce a syngas, with subsequent processing to allow capture of a pure stream of CO2. As shown in Fig. 2.3, pre-combustion decarbonization adds flexibility, as a variety of products can be made including electricity and fuels such as hydrogen, syngas, SNG (synthetic natural gas), or methanol. N 2, O 2, H 2O Post-combustion capture Flue gas Fuel Air CO2 separation Power and heat CO2 Pre-combustion capture Fuel CO2 Gasification or partial oxidation shift + CO2 separation H2 Air Power and heat N 2, O 2, H 2O O2 Air Air separation CO2 compression, transport, and storage N2 Oxyfuel combustion capture Fuel O2 Air CO2(H2O) Power and heat Air separation Recycle (CO2, H2O) N2 2.2 CO2 capture processes (IPCC, 2005). © Woodhead Publishing Limited, 2010 32 Developments and innovation in CCS technology Flexibility for alternative products Natural gas Coal Biomass Waste CO2 Gasifier, reformer Gas treatment CO2 capture CCGT Alternatives or additionalities Electricity Heat H2 Synthesis gas (CO + H2) SNG Methanol Motor fuels 2.3 Pre-combustion capture options (CCGT = combined cycle gas turbine) (IEA, 2008). 2.2.1 Plant level modeling First, we define the system boundaries and the plant configuration. To assess the incremental cost of implementing CO2 capture, we also specify a reference case fossil energy plant without CO2 capture. Then process simulation software such as ASPEN or HYSYS is used to estimate steady-state mass and energy balances for the fossil energy plant. The process model sizes and characterizes all the equipment that is needed in the plant, and energy and material inputs and outputs. This forms the basis for estimating plant capital and operation costs, energy conversion efficiency or heat rate, and plant product mix. Generally, CO2 capture involves both extra capital costs and additional energy use, for example, for CO2 compression. Table 2.2 shows results from a recent review paper by the IEA (2008) that estimates the conversion efficiency for fossil power plants with and without CCS. 2.2.2 Economics of fossil energy plants with CO2 capture The main economic metrics used to assess fossil energy systems with CO2 capture are the plant capital investment cost given in $ or $/kW, the cost of electricity (or electricity and fuels), the avoided cost of carbon in $/tonne CO2, and the capture cost for carbon in $/tonne CO2. Plant capital investment cost Once the plant mass and energy flows have been determined, and plant equipment is sized, the total capital investment can be found. Plant investment cost is typically given in $/kW. Technology maturity is an important consideration in estimating plant capital costs. For current CO2 capture technologies, costs are moderately well © Woodhead Publishing Limited, 2010 Table 2.2 Characteristics of electric power plants with and without CO2 capture (IEA, 2008) Efficiency (LHV %) Electricity cost ($/MWh) Technology Start CO2 capture rate (%) With CO2 capture No CO2 capture With CO2 capture No CO2 capture With CO2 capture Reference plant (no CO2 capture) Coal steam cycle Coal steam cycle, oxyfuel Coal IGCC, Selexol1 Biomass IGCC Gas, CC, California Gas CC oxyfuel 85 85 90 90 85 85 85 85 85 95 2250–3200 1850–2500 2500–3100 2100–2600 2300–2800 1800–2400 2600–3000 1000–1200 800–1000 1250–1400 1500–2200 1300–2000 1900–2400 1500–2100 1600–2300 1300–2000 1900–2400 660–750 550–650 700–850 38 44 37 44 35 48 26 49 56 48 47 52 47 52 44 54 34 57 63 58 74–83 59–68 77–87 60–69 76–86 58–65 110–130 59–88 49–75 51–79 39 27–29 41–44 28–31 40–41 26 64–73 33–59 30–53 30–53 2010 2030 2020 2030 2010 2030 2025 2010 2030 2020 CC = combined cycle; IGCC = integrated gasification combined cycle. TM Dow Chemical Company. 1 Techno-economic analysis and modeling © Woodhead Publishing Limited, 2010 Investment costs ($/kW) 33 34 Developments and innovation in CCS technology known, because many of the processes such as gasification, reforming, and CO2 compression are used commercially. However, for advanced or future CO2 capture technologies, costs are more uncertain and projections must be made. Here it is important to specify whether the advanced technology plant is assumed to be the first of kind or the ‘nth’ plant (assuming the advanced technology has been built many times and has met its goals). Technology learning curves have been employed in some analyses to assess the transition costs for bringing advanced CO2 capture technology from the first plant to maturity (Kuuskraa, 2007; IEA, 2008). The conventions for estimating the plant investment cost are not completely consistent among studies in the literature. Indirect costs for installation, site preparation, engineering, project contingency, and interest during construction, are not always added to the equipment costs. Recent studies by the IPCC (2005) and the IEA (2008) attempted to adjust for these differences to put estimates from the literature on a consistent basis. Table 2.2 illustrates the investment costs for a variety of coal power plant options with and without CO2 capture in the 300–1000 MWe range (IEA, 2008). CO2 capture adds 40–100 % to the plant capital cost. Cost of electricity A second important metric is the cost of electricity from a fossil energy plant with CO2 capture, as compared to the cost of electricity for a similar type of plant without capture. The levelized cost of electricity (COE) is estimated for a power plant as follows: COE ($/kWh) = (CRF*Ccap + COMf + COMv + Cfeed – CRco ) [2.1] CO2 * CO2 ) where CRF is the capital recovery factor, Ccap is the total capital) investment cost ($), COMf is the annual fixed operation and*8760) maintenance (O&M) cost ($/ (CF*Cap year), COMv is the annual+variable O&M cost excluding feedstock ($/year), (Tax Cfeed is the annual feedstock cost ($/year) (e.g., coal, natural gas, biomass), CRco is the annual credit for co-products ($/year) (e.g., fuels), CF is the annual average plant capacity factor (%), Cap is the plant capacity (kW), 8760 is the number of hours in one year, TaxCO2 is the carbon tax, if applicable ($/ x E rate of the plant (tCO2/kWh). The tCO2), and ECO2 is the CO2 emissions feedstock cost per kWh of electrical output can be expressed as the product of the plant heat rate (kJ feed/kWh electricity) and the price of feedstock ($/ kJ). The variable O&M costs depend on required energy inputs and the prices of these inputs. The fixed O&M costs are often expressed as a fraction of the total plant capital cost, typically 3–5 % of the capital cost per year. © Woodhead Publishing Limited, 2010 Techno-economic analysis and modeling 35 The cost of electricity with and without CO2 capture is estimated in Table 2.2, based on studies by the IEA (2008) for current and future technologies. The efficiency is generally lower for power plants with CO2 capture and capital costs are higher, yielding an electricity cost premium of 2–6 cents/ kWh or 40–100 %. Avoided cost of CO2 emissions To compare carbon capture with other options for reducing carbon emissions, it is useful to estimate the avoided cost of CO2 emissions. For electricity plants, this is defined as the difference in the electricity cost per kWh divided by the difference in CO2 emissions per kWh compared to a reference system without CO2 capture (IPCC, 2005): LCavoided = (COEcapture – COEref ) ) (ECO2ref – ECO2c [2.2] capture where LCavoided is the levelized cost of avoided CO2 emissions ($/tCO2 avoided), COEcapture is the cost of electricity for the plant with capture ($/ kWh), COEref is the cost of electricity for a reference plant without capture ($/kWh), ECO2ref is the CO2 emissions rate of the reference plant (tCO2/kWh), and ECO2capture is the CO2 emissions rate of the capture plant (tCO2/kWh). Cost of CO2 capture A similar metric is the cost of CO2 capture, also in $/tCO2. This is useful for comparing to the market price of CO2, for example, for enhanced oil recovery: LCcapture = (COEcapture – COEref ) CO2 capture [2.3] where LCcapture is the levelized cost of captured CO2 emissions ($/tCO2) and CO2capture is the quantity of CO2 captured at the plant (tCO2/kWh). The cost of captured CO2 is always less than the avoided cost of CO2 emissions because the energy required to operate the CO2 capture system adds to the amount of CO2 emitted per kWh. Table 2.3 summarizes the emissions rates and costs for power plants with and without CO2 capture (IPCC, 2005). 2.2.3 Production of hydrogen and other fuels with CO2 capture Although much of the emphasis is on CO2 capture at fossil fuel electric power plants, pre-combustion decarbonization opens the possibility of making © Woodhead Publishing Limited, 2010 36 Developments and innovation in CCS technology Table 2.3 Emissions rates and costs associated with power plants with and without CO2 capture (IPCC, 2005) CO2 emissions rate (kgCO2/MWh) Electricity cost ($/MWh) Technology With CO2 No CO2 With CO2 No CO2 Cost of Cost of capture capture capture capture captured CO2 avoided CO2 ($/tonne CO2) ($/tonne CO2) Coal PC plant 92–145 NGCC 40–66 Coal IGCC 65–152 736–811 62–86 344–379 43–72 682–846 54–79 43–52 31–50 41–61 23–35 33–57 11–32 29–51 37–74 13–37 IGCC = integrated combined cycle; NGCC = natural gas combined cycle; PC = pulverized coal. hydrogen or other syngas-derived fuels from fossil resources with CO2 capture (Fig. 2.3). CO2 capture adds perhaps 20 % to the cost of producing hydrogen from coal (Ogden, 2003). 2.2.4 Cost of electricity: sensitivity to the value of carbon In the previous sections we presented results for the cost of electricity for fossil power systems with and without CO2 capture. In general, the cost of electricity is higher with CO2 capture, but carbon emissions are reduced by over 80 %. Figure 2.4 shows how the costs of electricity compare at different valuations of carbon (e.g., through a carbon tax). Plants with CCS are preferred for carbon taxes in the range of $40–70/tCO 2. 2.3 Carbon dioxide (CO2) transport This section describes the economics of transporting CO2 from the point of capture at large-scale industrial point sources to onshore or offshore storage sites. Three options are possible for transporting CO2: tanker trucks (onshore), pipelines (onshore and offshore), and ships (offshore). Tanker trucks have been deemed impractical for transporting the enormous quantities of CO 2 produced by large-scale industrial point sources. Consequently, this section focuses on the economics of pipeline transport for onshore applications and pipeline and ship transport for offshore applications. Onshore pipeline transport is a proven technology with approximately 2400 km of large CO2 pipelines in operation globally (Gale and Davison, 2004; Zhang et al., 2006). The majority of these pipelines are used to supply enhanced oil recovery operations in the USA. Several studies identify pipeline transport as the most economical method for moving large volumes of CO2 © Woodhead Publishing Limited, 2010 Techno-economic analysis and modeling 37 0.25 Cost of electricity ($/kWh) 0.2 NGCC with CO2 capture NGCC no capture PC plant no capture PC plant w/CO2 capture IGCC plant no capture IGCC plant w/CO2 capture 0.15 0.1 0.05 0 0 25 50 Carbon tax ($/tonne CO2) 75 100 2.4 Cost of electricity from fossil power plants (c. 2010 technology) for different values of carbon tax. overland (Svensson et al., 2004; Doctor et al., 2005). Pipeline transport has also been identified as the most economical method for offshore transport of CO2 for distances less than 500–1000 km (Bock et al., 2003; Doctor et al., 2005; Wildenborg et al., 2005). For longer distances, ship transport may be preferable. 2.3.1 Pipeline transport The cost of pipeline transport is affected by the characteristics of both the pipeline route and the pipeline itself. Elements of the route that can impact cost include both the physical geography (e.g., river and road crossings, parks, terrain) and social geography (e.g. population density, regional labor and land costs, local acceptance) (Hendriks et al., 2003). In addition, pipeline characteristics, such as length, diameter, materials, the number of bends, and the need for booster stations, are important determinants of cost. Pipeline design Fluid flow models that use hydraulic equations for turbulent flow (Woodhill Engineering Consultants, 2002; Bock et al., 2003; Hendriks et al., 2003; Ogden et al., 2004; McCoy and Rubin, 2008; Vandeginste and Piessens, 2008) are useful in estimating pipe diameter since they include the parameters relevant to pipeline design (i.e., inlet and outlet pressures, pipeline length, © Woodhead Publishing Limited, 2010 38 Developments and innovation in CCS technology CO2 mass flow rate, pipeline roughness factor, elevation change along the segment, and CO2 density, viscosity, and average temperature) and are thus flexible in their application. There are practical constraints on pipeline operating conditions. To avoid two-phase flow, CO2 should be transported in the supercritical phase, which occurs at a pressure greater than 7.38 MPa (Skovholt, 1993). It is recommended that it is transported at pressures greater than 8.6 MPa where changes in compressibility can be avoided at a range of temperatures used for pipeline operation. Table 2.4 lists common design parameters for CO2 pipeline transport. Since pipelines are not available in continuous diameters, the pipeline diameter used for a particular project is constrained by the available discrete sizes, or nominal pipe size (NPS). The NPS generally corresponds to the external diameter in inches of commercially available pipelines (McCoy and Rubin, 2008). In some cases, it may be economically advantageous to design the pipeline with booster compressor stations every 150–300 km. If CO2 is recompressed at intervals, this allows use of smaller diameter, lower cost pipelines. However, there is a trade-off between lower pipe costs and the added costs of compression. These issues are discussed in Zhang et al. (2006), McCoy (2008), and Bock et al. (2003). Comparison of actual and calculated pipeline diameters The capacity, length, elevation difference, and actual diameter of several existing CO2 pipelines are known (Table 2.5) (Vandeginste and Piessens, 2008). Using this information, it is possible to compare the actual diameters with those calculated from the pipeline models provided by McCoy and Rubin (2008) and Vandeginste and Piessens (2008). Table 2.5 indicates that both models accurately estimate the diameters of the existing CO 2 pipelines. Table 2.4 Common design parameters for pipeline transport (Bock et al., 2003) Parameter Value Units Inlet pressure Minimum outlet pressure Average CO2 temperature Average CO2 density Average CO2 viscosity Pipeline roughness factor Pipeline capacity factor CO2 purity in pipeline Change in elevation 15.2 10.3 25 884 6.06 ¥ 10–5 4.57 ¥ 10–5 100 100 0 MPa MPa °C kg/m3 N–s/m2 meters % % meters © Woodhead Publishing Limited, 2010 Techno-economic analysis and modeling 39 Table 2.5 Comparison between actual and calculated pipeline diameter for existing CO2 pipelines Pipeline Capacity Length Elevation Actual NPS McCoy NPS Vandeginste (Mt/year) (km) difference diameter diameter NPS (m)1 (in) (in) diameter (in) Transpetco Sheep Mountain part 1 Sheep Mountain part 2 Bravo Weyburn 3.4 6.4 193 296 1094 893 12.6 20 12 18 14 18 9.3 360 464 24 24 24 7.4 1.8 351 330 955 46 20 14 20 14 20 14 1 Elevation difference represents a decrease in the elevation between the start and end points of the pipeline. Note: For the calculated values, the flow rate (capacity), length, and elevation change given in the table for each specific pipeline are used. The inputs listed in Table 2.4 are used for the unknown parameters. Offshore pipeline design Woodhill Engineering Consultants (2002), Dahowski et al. (2005), and Bock et al. (2003) examine offshore CO2 pipeline design and cost and note two significant differences between onshore and offshore pipeline design. First, booster stations are impractical for offshore pipelines so long offshore pipelines may require larger diameters than equivalent onshore pipelines in order to maintain pipeline pressure. Second, in designing offshore pipelines one must consider not only the change in pressure between the inlet and outlet, but also the gravity head gain due to the large decrease in elevation from the shore to the outlet at –2000 to –3000 m. Hence, the allowable pressure drop is much greater for offshore pipelines, which may reduce the diameter required for these pipelines. Pipeline cost For onshore CO2 pipelines, the costs include capital costs (engineering, installation, and materials) and operations and maintenance (O&M) costs (monitoring, inspection, and repair). If booster stations are required, additional capital costs and O&M costs are incurred. The energy cost for operating the booster pump or compressor can be a significant annual expense. Onshore pipeline capital costs We surveyed several studies that estimate onshore CO2 pipeline capital costs, including (Woodhill Engineering Consultants, 2002; Bock et al., 2003; © Woodhead Publishing Limited, 2010 40 Developments and innovation in CCS technology Hendriks et al., 2003; Parker, 2004; McCoy and Rubin, 2008). Based on these studies, average pipeline capital cost functions were developed for six discrete pipeline lengths from 50–500 km and several nominal pipe sizes from 4–30 inches. These functions were used to derive Equation 2.4 for calculating pipeline capital cost as a function of pipeline NPS and length: C = 32.086L–0.033D [2.4] where C is the capital cost (2005$/m), L is the pipeline length (km), and D is the nominal pipe size (in). The capital cost per meter shows very little dependence on overall pipeline length L and is approximately linear in D. Capital cost estimates given by Equation 2.4 represent average CO2 pipeline construction costs in the USA. Several project-specific factors can influence the actual cost of construction, including population density, physical terrain, regional location, and river and road crossings. In particular, regional cost variations in the USA can exceed 30 % (McCoy and Rubin, 2008) and construction in urban areas or rocky, marshy, or mountainous terrain can significantly increase the installation cost. Another issue that can affect estimates of construction costs is the observed rapid escalation of the costs of the labor and materials required for building pipelines over the past few years. An equipment cost index (e.g. Marshall and Swift) that accounts for this escalation should be used to adjust costs of older studies. The literature provides a range of fixed O&M costs for onshore pipelines between 0.5 and 4 % of the total capital cost with an average of 2.2 %. The levelized cost of onshore pipeline transport ($/tCO2 transported) is shown in Fig. 2.5 as a function of CO2 flow rate and pipeline length. The cost of CO2 transport scales approximately linearly with the pipeline length and shows strong scale economies with flow rate, varying approximately as the flow rate to the –0.6 power. For a 100 km pipeline, the levelized cost is between $1 and $2.50/tCO2 for plants producing > 5000 tCO2 per day. The levelized cost increases substantially for longer pipelines, but is still between $4 and $10/tCO2 for a 500 km pipeline transporting >5000 tCO2/day. Because the technology associated with onshore pipeline transport is mature, costs are not expected to benefit from technological learning in the future. Offshore pipeline capital costs Several studies estimate offshore pipeline costs for scenarios in which CO2 is injected directly into the ocean at depths exceeding 2000 m (Sarv, 2001; Woodhill Engineering Consultants, 2002; Bock et al., 2003; Doctor et al., 2005). Fig. 2.6 compares the levelized cost of onshore and offshore pipelines for a transport distance of 500 km. Total offshore costs are 2.3–2.6 times larger than equivalent onshore costs. © Woodhead Publishing Limited, 2010 Techno-economic analysis and modeling 35.00 100 km 41 500 km Pipeline levelized cost ($/tonne CO2) 30.00 25.00 20.00 15.00 10.00 5.00 0.00 0 5000 10 000 15 000 20 000 CO2 mass flow rate (tonnes/day) 25 000 30 000 2.5 Levelized cost for onshore pipeline transport. Levelized cost ($/tonne CO2) 40.00 Offshore 35.00 Onshore 30.00 25.00 20.00 15.00 10.00 0.00 0.00 0 5000 10 000 15 000 20 000 25 000 CO2 mass flow rate (tonnes/day) 30 000 35 000 2.6 Comparison of onshore and offshore pipeline costs for a 500 km transport distance. 2.3.2 Ship transport Presently, there are only four ships worldwide that operate specifically for CO2 transport. These ships are small-scale vessels used primarily for distributing food-grade CO2 with capacities between 1000 and 1500 m3 (Aspelund et al., 2006). In order to handle the large quantities of CO2 associated with CCS, much larger vessels would be required. As these vessels do not currently exist, cost estimates are largely based on existing LPG ships that operate © Woodhead Publishing Limited, 2010 42 Developments and innovation in CCS technology under similar conditions to those required for CO2 transport (Aspelund et al., 2006). The processes involved in ship transport include liquefaction, intermediate storage, loading, ship transport, and unloading at either an onshore port or an offshore injection platform. Transport system design Several studies examine the cost of CO2 transport by ship (Sarv, 2001; Bock et al., 2003; Svensson et al., 2004; Doctor et al., 2005; Aspelund et al., 2006). We follow the discussion in Aspelund et al. (2006) which includes a detailed description of each system component and, thus, provides a good template for system design. Prior to ship transport, CO2 is compressed, dried, cleaned of unwanted components, and liquefied. Liquid CO2 is then stored in either caverns or semi-pressurized steel tanks and a loading system transfers CO2 from storage to the ship and includes piping, a marine loading arm, pumps, and an export building. The ship then transports CO2 to an offshore injection platform, where it is unloaded. Offshore unloading of a cryogenic liquid has not been performed for any previous process, but Aspelund et al. (2006) describes a novel technology for this system, which includes a submerged turret loading system, piping, and pumping, expansion, and heating systems. It is assumed that CO2 will be injected in batches while the ship is connected to the platform. Ship transport costs Given the number of liquefiers, storage tanks, ships, and loading and unloading systems, the capital and O&M costs for a particular project can be identified. Cost estimates are listed in Table 2.6. Figure 2.7 shows the calculated levelized cost of ship transport for CO2 mass flow rates from 4000–30 000 tonnes/day (1.5–11 Mt/year) given the reference parameters in Table 2.6. In this case, the levelized cost of ship transport is $22–43/tCO2. Liquefaction accounts for the largest portion of the total transport cost (50–64 %) and the cost does not decline with scale since the liquefier capacity in this case is fixed and the variable cost of electricity is significant. In fact, liquefaction accounts for ~88 % of total energy use in the transport chain and ~93 % of the total cost of energy. Consequently, any reduction in this cost can significantly decrease the cost of transport. Aspelund et al. (2006) discusses several methods for reducing the energy requirement for liquefaction, including increasing the inlet pressure and decreasing the impurities in the feed. Storage, loading, and unloading system costs benefit from economies of scale since these systems are better utilized as the CO2 flow rate increases. Ship costs account for 17–23 % of total costs and exhibit cost spikes when additional ships are required. © Woodhead Publishing Limited, 2010 Techno-economic analysis and modeling 43 Table 2.6 Reference parameters for cost analysis (Bock et al., 2003; Svensson et al., 2004; Doctor et al., 2005; Aspelund et al., 2006) Parameter Value Offshore distance Electricity price Bunker oil price Natural gas price 500 0.05 309 8 Units km $/kWh $/tonne oil $/GJ Capital costs 50 Liquifier (1 Mt CO2/year) Steel storage tank (3000 m3) 10 Loading system 50 Semi-refrigerated ship (20 000 m3) 54 Unloading system 60 Million $ Million $ Million $ Million $ Million $ O&M costs Non-fuel O&M for ships 4.7 Non-energy O&M for other components 2 Liquefier energy use 110 Loading energy use 0.2 Ship energy use 0.6 Unloading energy use 0.65 Harbor tax 40 000 % of capital % of capital kWh/t CO2 kWh/t CO2 tonnes oil/hr kWh/t CO2 $ 50.00 Liquefaction 45.00 Storage Loading Levelized cost ($/tonne CO2) 40.00 Unloading 35.00 Tanker ships 30.00 25.00 20.00 15.00 10.00 5.00 0.00 4000 6000 8000 10 000 12 000 14 000 16 000 18 000 20 000 25 000 30 000 CO2 mass flow rate (tonnes/day) 2.7 Levelized cost of ship transport. 2.3.3 Comparison of pipeline and ship transport costs for offshore injection When transporting CO2 to offshore injection sites, studies indicate that pipelines are less expensive than ships at distances less than 500–1000 km (Sarv, © Woodhead Publishing Limited, 2010 44 Developments and innovation in CCS technology 1999; Bock et al., 2003; Doctor et al., 2005). Based on the cost estimates in this chapter, ship transport becomes more economical than pipelines at distances greater than 750 km (Fig. 2.8). Since pipeline transport benefits from economies of scale more than ship transport, the breakeven distance is expected to shift to longer distances as the CO2 mass flow rate increases. However, since booster compression is difficult with offshore pipelines, the maximum length of these pipelines may be limited. Given that early offshore CCS projects will likely be sited in preferred sites near shore, pipelines are likely to be the preferred mode of transport in the near term unless ship transport costs can be significantly reduced. Ship transport may be favored for long-distance transport (> 500 km) and in cases where the location of injection sites changes and flexibility in routing is required. 2.4 Carbon dioxide (CO2) injection This section describes the economics of injecting CO2 into geologic reservoirs for long-term storage. CO2 can be injected for ‘storage-only’ into deep saline aquifers or depleted oil and gas reservoirs or it can be used to enhance recovery of valuable fossil fuels, such as oil, natural gas, and coalbed methane. This section begins with an overview of models for injection site infrastructure requirements and then discusses the costs of the various components for each reservoir type. 120.00 Ship transport Offshore pipeline Levelized cost ($/tonne CO2) 100.00 80.00 60.00 40.00 20.00 0.00 0 200 400 600 800 1000 1200 1400 Offshore distance (km) 1600 1800 2.8 Comparison of pipeline and ship costs at various offshore distances (8000 tCO2/day). © Woodhead Publishing Limited, 2010 2000 Techno-economic analysis and modeling 2.4.1 45 Injection site design To estimate the cost of CO2 injection, it is necessary to calculate the required number of injection wells and the extent of the underground CO2 plume. The number of injection wells can be derived from the maximum injection rate per well, which is dependent on the specific characteristics of a target reservoir (e.g., permeability, porosity, pressure, and thickness). Ahmed (2006) provides a detailed review of the reservoir fluid flow equations that can be used to model CO2 injection rates. These equations address steady-state, pseudo-steady-state, and transient (unsteady-state) flow regimes (Ahmed, 2006). Several studies use the steady-state equation for radial flow of an incompressible fluid to model the maximum injection rate from a single well into a reservoir (Hendriks, 1994; Ogden et al., 2004; Middleton and Bielicki, 2009): qwell = 2p kh(pe – pw ) r m ÈÍln e ˘˙ r Î w˚ [2.5] where qwell is the injection rate (m3/s), k is the absolute permeability (m2), h is the reservoir thickness (m), re is the radius of influence of the well (m), pe is the pressure at re and is commonly the initial reservoir pressure (Pa), pw is the bottomhole injection pressure (BHIP) (Pa), rw is the wellbore radius (m), and m is the viscosity of CO2 at reservoir pressure and temperature (Pa–s). This steady-state model makes the simplifying assumption that flow is constant throughout the reservoir and that pressure at every location in the reservoir remains constant in time. McCoy (2008) has extended the steady-state model to include the effects of multiple wells and finds that injectivity decreases as the number of wells at a site increases. Consequently, the maximum injection rate of a well is likely to be smaller than predicted by models that don’t consider the effects of neighbouring wells. The maximum extent of the underground CO2 plume over the life of the project is important since it provides the radius of influence (re) used in calculating the injection rate and also identifies the area of influence used to identify site characterization costs. Various studies have developed models for calculating plume radius for different reservoir types (Hendriks, 1994; Bock et al., 2003; Nordbotten et al., 2005; McCoy, 2008). 2.4.2 Carbon dioxide (CO2) injection for storage only Two geologic reservoir types are commonly considered for long-term storage of CO2 without enhanced recovery: deep saline aquifers and depleted gas reservoirs. A typical CO2 injection site includes injection wells and surface © Woodhead Publishing Limited, 2010 46 Developments and innovation in CCS technology equipment (e.g., distribution pipelines and headers). In some cases, compressors or pumps may be required to achieve the required wellhead injection pressure at each well. Costs include well drilling, surface equipment, permitting, and site characterization. Deep saline aquifers Given reservoir and injection parameters, flow equations can be used to determine the maximum plume radius and maximum injection rate for a target aquifer. Table 2.7 provides parameters for two representative saline aquifers and lists the calculated plume radius and injection rate for each aquifer. The injection rate is highly sensitive to changes in certain reservoir parameters like permeability and thickness and can range from tens to thousands of tonnes CO2 per day. Several studies limit the injection rate per well to 2500–3400 t/day (Hendriks et al., 2004; Ogden et al., 2004; McCoy, 2008). Site characterization costs Given the injection rate and plume radius, the number of required injection wells and area of the CO2 plume (or ‘area of review’) can be calculated. Site characterization costs include 3-D seismic imaging of the area of review, drilling of characterization wells, and data processing and modeling services. McCoy (2008) estimates these costs as $38 610/km2 for 3-D imaging, $3 000 000 per well for drilling of characterization wells, and 30 % of the total cost for data processing, modeling, and other services. One well is required for every 65 km2 of the area of review. Equation 2.6 describes Table 2.7 Common aquifer and injection parameters (Nordbotten et al., 2005; Stauffer et al., 2009) Input parameter Cold/shallow Hot/deep Units Wellhead injection pressure Reservoir pressure (pe) Maximum BHIP (pw) Reservoir temperature Reservoir CO2 viscosity (m) Reservoir CO2 density (r) Reservoir depth (d) Reservoir thickness (h) Porosity (F) Permeability (k) 10.3 10 15 35 5.77 ¥ 10-5 714 1000 30 0.15 1.97 ¥ 10–14 10.3 30 45 155 3.95 ¥ 10–5 479 3000 30 0.15 1.97 ¥ 10–14 MPa MPa MPa °C Pa–s kg/m3 m m 5.9 5300 km/well tonnes/day/well Calculated parameter Plume radius (re) @ 20 years 4.8 Max injection rate (qwell) 1850 © Woodhead Publishing Limited, 2010 m2 Techno-economic analysis and modeling 47 the total site characterization cost (corrected to 2005$) as a function of the area of review: Csite = 117 344A + 2.70 ¥ 106 [2.6] where A is the area of review (km2). In developing an aquifer site for CO2 injection, permitting studies must be conducted and land, mineral leases, and permits must be purchased. The estimated average cost is approximately $23 000 per well (Bock et al., 2003; Bank and Kuuskraa, 2006). Well drilling costs Well drilling costs include the costs of drilling and completing wells for CO2 injection. Since limited data is available on the costs of drilling wells specifically for CO2 injection, most studies assume that the costs will be similar to those for drilling onshore oil wells in the USA (Bock et al., 2003; McCoy, 2008; Eccles et al., 2009; Stauffer et al., 2009). Based on 2004 Joint Association Survey (JAS) data, Equation 2.7 describes the well drilling cost as a function of well depth (API, 2007): Cdrill = (–3.9 ¥ 10–8d3 + 4.00 ¥ 10–4d2 – 0.84d + 903)d [2.7] where d is well depth (m) and Cdrill is the drilling cost (2005$/well). For typical well depths of 1–3 km, the cost is $0.4–$2.7 million per well. Surface equipment Several studies assume that surface equipment costs for CO2 injection are similar to the costs of equipping water injection wells for secondary oil recovery (Bock et al., 2003; McCoy, 2008; Eccles et al., 2009). These studies use data published by the Energy Information Administration (EIA, 2007) on lease equipment costs for secondary oil recovery in West Texas. Equations 2.8 and 2.9 were developed from 2005 EIA data using the approach employed by McCoy (2008): Cequip = 0.0121d2 – 21.745d + 53 818 [2.8] [2.9] ÈCequip, N wells > 20 Í 0.5 Cequip,N = Í Ê 21 ˆ C ÍÎ equip ÁË N wells ˜¯ , N wells ≤ 20 where Cequip is the surface equipment cost (2005$/well). O&M costs include normal daily expenses, surface maintenance, and subsurface maintenance and are derived from EIA (2007) data for secondary oil recovery: © Woodhead Publishing Limited, 2010 48 Developments and innovation in CCS technology COM = 8.76d + 13 267 [2.10] where COM is the O&M Cost (2005$/well/year). McCoy (2008) reports the monitoring cost to be ~$0.02/tCO2 injected. Assuming a project life of 20 years and capital recovery factor (CRF) of 11.75 %, the levelized cost of CO2 injection can be calculated. Figure 2.9 shows the levelized cost for CO2 injection into a cold/shallow aquifer for several annual CO2 flow rates. The contribution of each cost component to the overall cost is also shown. The most surprising finding is that site characterization contributes ~90 % of the total levelized cost while drilling costs contribute less than 7 %. In the hot/deep case, well drilling costs are significantly larger so well drilling and site characterization costs account for ~30 % and ~60 % of the total cost, respectively. The levelized cost of CO2 injection varies from $1.70 to $2.90/tonne CO2 for the cold/shallow case and from $1.40 to $3.30/tonne for the hot/deep case. In both cases, site characterization costs are significant and consequently methods to reduce these costs could substantially reduce the cost of CO2 injection. Two potential methods are targeting aquifers that generate smaller plumes (e.g., thick reservoirs) and using sites that have been previously characterized. $3.50 Land, permitting, and mineral cost O&M and monitoring cost $3.00 Site characterization cost Levelized cost ($/tonne CO2) Injection equipment cost Well drilling cost $2.50 $2.00 $1.50 $1.00 $0.50 $0.00 1000 4000 8000 12 000 16 000 CO2 mass flow rate (tonnes/day) 20 000 30 000 2.9 Contribution of each cost component to the total levelized cost of CO2 injection into a cold/shallow aquifer. © Woodhead Publishing Limited, 2010 Techno-economic analysis and modeling 49 Depleted gas reservoirs Most studies of CO2 injection into depleted gas reservoirs focus on type I reservoirs, where natural gas is produced via pressure depletion (Oldenburg et al., 2001, 2004; Bock et al., 2003; Zhang et al., 2007; Hughes, 2009). These reservoirs are attractive because they are proven long-term geologic traps for gas storage, have already been extensively characterized, and have existing gas production infrastructure that may be converted for CO 2 injection. Unlike saline aquifers where only about 2 % of the pore space is available for CO2 storage, 80–95 % of this space may be available in type I reservoirs. This means that less reservoir volume is required for storing a given amount of CO2. These reservoirs are also favored since they are appropriate for enhanced gas recovery (EGR) (see Section 2.4.3). Although depleted gas reservoirs have several advantages over saline aquifers for CO2 storage, there are also some disadvantages. First, many gas production wells have been drilled into these reservoirs and there is a risk of leakage if the abandoned wells are not capped appropriately. Second, pressures in depleted type I gas reservoirs are typically 2–5 MPa (Oldenburg et al., 2001), which is significantly smaller than the projected bottom hole CO2 injection pressure (15–35 MPa). Hughes (2009) examines techniques for reducing BHIP, but concludes that a high-tech flow control device will be required at the base of the tubing in order to maintain flow. The need for this device could present a serious technical challenge to CO2 injection into depleted gas reservoirs. The equipment required for CO2 storage is almost identical for depleted gas reservoirs and saline aquifers. The exception is the flow control devices that will likely be required for the former. The characteristics of depleted gas reservoirs fall within a large range and thus widely different injection rates are possible (Bock et al., 2003; Oldenburg et al., 2004; Hughes, 2009). In order to capture the impacts of different injection rates on cost, two injection rates are modeled: 150 and 1500 tonnes per day. Based on these rates, the number of injection wells is estimated and storage costs can be derived. Storage costs in depleted gas fields differ from those in saline aquifers since these sites have been previously characterized and developed for gas production. Consequently, the permitting cost is reduced to ~$9000 per well (Bank and Kuuskraa, 2006) and site characterization cost is eliminated. Furthermore, it is assumed that existing gas production wells can be converted to CO2 injection wells at one third of the cost of drilling new wells (Oldenburg et al., 2004). However, new injection equipment must be installed since existing gas distribution equipment may not be sufficient for the quantities and pressures of supercritical CO2. Consequently, injection equipment, O&M, and monitoring costs are consistent with injection into aquifers (see p. 47). The cost of flow control devices is not known as this technology has not yet been developed. © Woodhead Publishing Limited, 2010 50 Developments and innovation in CCS technology The levelized costs for the two injection rates (150 and 1500 tonnes/day/ well) are estimated to be ~$1.40/tonne and ~$0.20/tonne CO2, respectively. The smaller injection rate requires additional wells and thus has a much larger cost. It is evident that the cost of CO2 storage in depleted gas reservoirs is substantially lower than storage in saline aquifers because costly site characterization is unnecessary and injection wells cost less since they are converted from existing production wells. If new injection wells are drilled, the levelized cost increases 50–60 % for both injection rates, but is still lower than the cost for storage in saline aquifers. 2.4.3 Carbon dioxide (CO2) injection for enhanced fossil fuel recovery In some cases, CO2 injection can enhance the recovery of valuable fossil fuels and thus generate revenue that can be used to offset the costs of CCS. In this section, the costs associated with enhanced gas recovery (CO2–EGR), enhanced oil recovery (CO2–EOR), and enhanced coalbed methane recovery (CO2–ECBM) are reviewed. Although storage capacities associated with these pathways are relatively small, they represent near-term opportunities for reducing the cost of CCS while advancements in cost-effective capture technologies are developed. Site design For enhanced fossil fuel recovery, the required number of production and injection wells can be estimated using a ‘rule of thumb’ method described in Bock et al. (2003) and given by Equation 2.11. È(Q /eff )˘ N iwells = Í CO2 ˙ (I : P ) Î qproduct ˚ [2.11] where Niwells is the number of injection wells, QCO2 is the total design mass flow rate of CO2 (scm CO2/day), eff is the CO2 effectiveness factor [scm CO2/scm methane (CH4) or scm CO2/bbl oil], qproduct is the average gas or oil production rate per well (scm CH4/day/well or bbl oil/day/well), and I:P is the injector to producer well ratio. The CO2 effectiveness factor represents the quantity of CO2 stored for every scm CH4 or barrel of oil produced. Common ranges for the input parameters are listed for each of the reservoir types (Table 2.8). In addition to injection and production wells, all enhanced fossil fuel recovery sites must include surface equipment for distributing CO2 and processing the produced fuel for sale. In some cases, water disposal equipment and/or CO2 separation and recycling equipment are required. © Woodhead Publishing Limited, 2010 Techno-economic analysis and modeling 51 Table 2.8 Common ranges for input parameters for Equation 2.11 (Bock et al., 2003; Pashin and McIntyre, 2003; Reeves et al., 2003; Oldenburg et al., 2004; EIA, 2007; Durucan and Shi, 2009; Robertson, 2009) Reservoir type CO2 effectiveness factor Average gas or oil production rate EGR EOR ECBM 1.5–3 1400–140 000 85–227 40–70 1.5–10 1700–14 000+ Injector to producer well ratio 1:1 1:1.1 1:1 Enhanced gas recovery (CO2–EGR) In type I gas reservoirs, gas production declines over time as reservoir pressure is depleted. Pressure depletion recovers 80–90 % of original gas in place (OGIP), leaving about 10–20 %. It is postulated that CO2 injection into these reservoirs could allow for enhanced recovery of the remaining gas through repressurization of the reservoir and displacement of methane by CO2. Consequently, CO2–EGR could potentially generate revenue through sale of natural gas while storing CO2. With CO2–EGR, it is assumed that all of the production equipment is already in place so incremental capital costs include conversion of existing production wells to CO2 injection wells, installation of CO2 injection and distribution equipment, and permitting. Equipment capital costs are derived using the equations for storage in depleted gas reservoirs outlined on p. 49. O&M costs include O&M for production and injection equipment, monitoring, and gas processing, treatment, and compression. The O&M cost for injection equipment is given by equation 2.10 and the production equipment O&M cost is derived from EIA (2007) data for gas production in West Texas: COMp = 405.81d0.5517 [2.12] where COMp is the annual O&M cost of gas production (2005$/well) and d is well depth (m). Monitoring is estimated to be $0.02/tCO2 and the cost of natural gas treatment and compression is estimated by Bank and Kuuskraa (2006) to be ~$0.025 per scm of CH4. CO2 separation and recycling equipment may be necessary if substantial CO2 breakthrough occurs at the production wells and can add substantial cost. Incremental gas production associated with CO2–EGR is estimated to be 80–90 % of annual total production (Oldenburg et al., 2001, 2004). The incremental revenue from gas sales is calculated by multiplying the incremental gas production by the wellhead gas price and assuming a royalty tax of 12.5 %. A sensitivity analysis given the baseline parameters in Table 2.9 and wellhead natural gas price of $4/GJ indicates that the levelized storage cost is most sensitive to the CO2 effectiveness factor, average gas production © Woodhead Publishing Limited, 2010 52 Developments and innovation in CCS technology Table 2.9 Reservoir characteristics for a baseline case and at three depths (EIA, 2007; Hughes, 2009) Scenario Average depth (m) Average gas production rate (scm/day/well) CO2 effectiveness factor (scm CO2/scm CH4) Shallow Medium Deep Baseline 1220 2439 3659 1000 7000 7000 14 000 7000 2.8 1.7 1.4 3 $20.00 Levelized cost ($/tonne CO2) $10.00 $0.00 –$10.00 –$20.00 –$30.00 CO2 effectiveness factor Average gas production rate Natural gas price Well depth –$40.00 –$50.00 –$60.00 –100 % –50 % 0% 50 % 100 % 150 % Percentage change in parameter 200 % 250 % 2.10 Sensitivity of levelized cost to various parameters. rate, and the natural gas price (Fig. 2.10). This figure is generally applicable to all enhanced fossil fuel recovery operations. In particular, high prices for the produced gas or oil improves project economics through increased revenue while a reduction in the CO2 effectiveness factor results in improved economics since more product (i.e., revenue) is produced for each unit of CO2. Reservoirs with high average production rates also have better economics since they generate more revenue per well. The levelized cost of CO2 storage is calculated for three reservoir depths given the parameters in Table 2.9 and a wellhead natural gas price of $4/ GJ. The storage cost ranges from –$8.00 to –$11.00/tCO2, which suggests that revenue generated from methane recovery can offset CO2 storage costs. However, if a CO2 capture and transport cost of $50/tonne is assumed, CO2–EGR would require a $40/tCO2 carbon credit or a wellhead natural gas price >$7/GJ in order to be economic. © Woodhead Publishing Limited, 2010 Techno-economic analysis and modeling 53 Enhanced oil recovery (CO2–EOR) Although CO2–flood enhanced oil recovery is a proven technology that is currently used at over 80 sites worldwide (Bock et al., 2003), no CO2–EOR projects currently utilize CO2 from power plants. CO2–EOR is attractive since it can improve the recovery of domestic oil while storing CO2 and producing substantial revenue from oil sales. This technique is employed at sites that have already undergone primary and secondary recovery so most of the infrastructure for oil production and CO2 injection is already in place. Capital costs for converting a site to CO2–EOR include: (i) conversion of water injection and/or production wells to CO2 injection wells; (ii) workover of existing production wells and equipment; (iii) installation of equipment for distributing and injecting CO2; and (iv) installation of CO2 separation, compression, and recycling equipment. The equations for calculating the capital costs of converting existing wells to CO2 injection wells, installing CO2 distribution and injection equipment, and permitting are summarized on pages 47–49. An equation for the cost of upgrading existing production wells and equipment for CO2–EOR is derived from EIA (2007) estimates of additional lease equipment costs for water flooding in West Texas: Cprod = 91 510ln(d) – 567 823 [2.13] where d is well depth (m). CO2 separation and recycling equipment costs are determined using the design and costs given in Bock et al. (2003). O&M costs include O&M for production and injection equipment, monitoring, CO2 processing, and fluid lifting. The O&M cost for production and injection equipment is given by Equation 2.10 and the monitoring cost is assumed to be $0.02/tCO2. The CO2 processing O&M cost is estimated to be 1 % of the oil price per Mscf CO2 (e.g., $0.25/Mscf at $25/barrel) and the cost for fluid lifting is assumed to be $0.25/barrel of total liquid production (Advanced Resources International, 2006). Annual revenue from the sale of oil is calculated by multiplying annual oil production by the first purchase oil price and assuming a royalty tax of 12.5 %. The first purchase oil price is the price received at the well and can be derived from the marker oil price (Advanced Resources International, 2006). Based on the annual revenue and costs, the levelized cost of CO 2 storage is determined (Table 2.10). Table 2.10 indicates that the storage cost associated with CO2–EOR is negative even at a relatively low oil price of $20/bbl. For marker oil prices of $35 and $60/bbl, the breakeven cost of CO2 is estimated to be $50/tonne CO2 and $108/tonne CO2, respectively. This is consistent with McCoy & Rubin (2009), which estimates the breakeven cost of CO2 to be $117–195/ tonne CO2 for a marker oil price of $60/bbl. Given that most estimates of CO2 capture and transport costs for power plants are less than $50/tonne CO2, this model suggests that CO2–EOR should be economically viable for © Woodhead Publishing Limited, 2010 54 Developments and innovation in CCS technology Table 2.10 Reservoir characteristics and levelized cost for three oil fields (Bock et al., 2003; McCoy and Rubin, 2009) Average depth (m) Average oil production rate (bbl/day/well) CO2 effectiveness factor (scm CO2/barrel oil) Storage cost1 ($/tonne CO2) Baseline SACROC, Kelly Snyder Field Northeast Purdy Unit 1220 2042 40 35 170 103 –$13.82 –$11.35 2499 41 82 –$5.89 Oil field 1 Assuming $20/bbl marker oil price, maximum CO2 recycle ratio of 3, and design CO2 mass flow rate of 8000 tonnes/day. most CO2 sources at oil prices greater than ~$35/bbl. Despite the positive economics of CO2–EOR, the limited locations and low storage capacity of these sites suggest that opportunities for storing power plant CO2 emissions via CO2–EOR will be limited. Enhanced coalbed methane (CO2–ECBM) Deep unmineable coal beds are valued for the significant quantities of methane that they contain. Generally, this methane is extracted by pressure depletion and dewatering of the reservoir. However, CO2 can effectively enhance methane recovery since its higher affinity for coal results in desorption and displacement of adsorbed methane, resulting in additional recovery of 10–20 % of OGIP (Reeves et al., 2004; Robertson, 2009). CO2–ECBM can be employed as a secondary recovery technique at sites that have previously undergone primary recovery or as part of primary recovery at undeveloped sites. Reeves et al. (2004) find that undeveloped sites provide better economics since there is a larger methane resource with which to offset CO2 storage costs. Capital costs for new CO2–ECBM developments include permitting, mineral rights, and land, drilling of CO2 injection and methane production wells, installation of equipment for water disposal, distributing CO2, methane, water, and treating and compressing methane for sale. CO2 recycling equipment may be necessary if substantial CO2 breakthrough occurs at the production wells. However, several studies suggest that CO2 breakthrough is negligible with appropriate well spacing (Reeves, 2001; Robertson, 2009). Bock et al. (2003) and Bank and Kuuskraa (2006) provide per-well costs for permitting, mineral rights, and land costs. The average of these values is approximately $23 000 per well. Drilling costs for both production and injection wells are given by Equation 2.7 and CO2 injection equipment costs are given by Equations 2.8 and 2.9. Methane production equipment costs include gas gathering pipelines, production well equipment, and electric © Woodhead Publishing Limited, 2010 Techno-economic analysis and modeling 55 power infrastructure. Gas gathering and electric power equipment costs are estimated by Bank and Kuuskraa (2006) as $58 000/well and $16 000/well, respectively. Production well equipment costs are reported by the EIA (2007) for the four primary coalbed methane sites in the USA (Table 2.11). Water disposal equipment design and costing for shallow underground re-injection are given in Bank and Kuuskraa (2006). O&M costs are divided into four components: well maintenance, monitoring, water disposal, and natural gas treatment, processing, and compression. O&M costs for injection wells are determined using Equation 2.10 and O&M costs for CBM production wells are estimated using EIA (2007) data for CBM projects in each of the four basins. Monitoring is estimated to be $0.02/tonne CO2 and water disposal O&M is estimated by Bank and Kuuskraa (2006) to be $0.10/barrel of water. The cost of gas treatment and processing is estimated by Bank and Kuuskraa (2006) to be $0.025 per scm CH4. Annual revenue from the sale of natural gas is calculated by multiplying annual gas production by the wellhead gas price and assuming a royalty tax of 12.5 %. The levelized cost of CO2 storage for the four primary coal bed methane basins in the USA is estimated using the input parameters from Table 2.11 and a wellhead gas price of $4/GJ. These estimates range from –$12.00/tCO2 in the San Juan Basin to $26.00/tCO2 in the Appalachian Basin. In fact, the only basin in which methane recovery offsets CO2 storage costs is the San Juan basin which has relatively high methane production. In this ‘best case’ basin, the breakeven cost of CO2 for wellhead gas prices of $6/GJ and $10/ GJ are $23/tCO2 and $46/tCO2, respectively. This analysis suggests that the potential for economic CO2–ECBM projects will be limited to sites with very high gas production and, even in these cases, either high wellhead gas prices or significantly reduced CO2 capture costs will be required. Since gas production and CO2 injection rates have a large impact on storage costs, technologies that can improve these rates (e.g., horizontal wells and Table 2.11 Reservoir characteristics of primary coalbed methane basins in USA and baseline case (Pashin and McIntyre, 2003; Reeves et al., 2003; Bank and Kuuskraa, 2006; EIA, 2007; Durucan and Shi, 2009) Coal basin Average Average gas Average water CO2 Production depth production rate production rate effectiveness well (m) (scm/day/well) (bbl/day/well) factor (scm equipment CO2/scm CH4) cost ($/well) Appalachian Black Warrior Powder River San Juan Baseline case 610 610 457 945 600 1700 3000 3000 14 000 7000 3 20 50 100 100 3 2 5 3 3 © Woodhead Publishing Limited, 2010 $26 000 $30 000 $16 000 $66 000 – 56 Developments and innovation in CCS technology nitrogen injection) could potentially reduce future costs (Durucan and Shi, 2009). Several studies have examined the injection of flue gas rather than pure CO2 since it would eliminate the need for CO2 capture and nitrogen improves gas production (Reeves et al., 2004; Durucan and Shi, 2009; Robertson, 2009; Zarrouk and Moore, 2009). These studies find improved overall economics, but minimal CO2 storage benefits and higher costs per tCO2 since much smaller quantities of CO2 are injected (Reeves et al., 2004; Robertson, 2009). 2.5 Carbon dioxide (CO2) capture and storage (CCS) system modeling In this section, we discuss the cost of a complete fossil energy system with CCS, drawing on the individual models described in Sections 2.2–2.4 for CO2 capture, transport, and storage (Table 2.12). We consider power plants in the range of 300–1000 MW, which produce 4000–25 000 tonnes of captured CO2 per day; CO2 transport systems capable of moving this amount of CO2 up to 500 km, and various schemes for CO2 injection and storage in geological formations such as saline aquifers and depleted oil and gas fields, including EGR, EOR, and ECBM. CO2 capture is the largest single cost involved in implementing CCS, accounting for $15–75/tCO2 captured. The transport cost of CO2 shows strong scale economies, decreasing with flow rate, and increasing with distance, with costs of perhaps $1–8/tCO2 for onshore pipelines, and three times that for offshore pipelines. Geological storage costs $0.5–5/tCO2. With enhanced recovery of fossil fuels, the cost of CO2 injection and storage can become negative, depending on the value of the produced oil or gas. Generic cost ranges are interesting because they give an order of magnitude on costs. However, more realistic system models are needed to look at the prospects for CCS for a particular region or situation. With the increasing availability of geographic information system data, it has become possible to do geographic specific case studies of fossil energy systems with CCS (Herzog, 2006; Johnson and Ogden, 2008; Johnson et al., 2008; Middleton and Bielicki, 2009). Existing CO2 sources and power plant locations, sequestration sites, and potential pipeline locations can be identified for a given region. The model develops an optimized design for CO2 pipelines to connect sources of CO2 and storage sites. Most techno-economic system models are static and assume a fixed demand. However, several scenarios for building up regional CCS-based systems over time have been developed and help to estimate the costs for making a multi-decade transition to a fossil energy system with CCS (Kuuskraa, 2007; IEA, 2008; Johnson et al., 2008). An example of an optimization model for a coal-based hydrogen production © Woodhead Publishing Limited, 2010 Techno-economic analysis and modeling 57 Table 2.12 Range of costs for each component of a CCS system CCS system component Capital cost CO2 capture Incremental capital cost vs plant w/o CO2 capture ∑ 300–1000 MWe Power Plant Coal PC $750–1000/kWe (+40–50 %) Coal IGCC $500–700/kWe (+25–40 %) NGCC $300–500/kWe (+50 %) ∑ 300–1000 MWth H2 Plant Coal gasification $–50 to +50 /kWth NG reformer $150–200/kWth (+60 %) CO2 transport Onshore pipeline ∑ 100 km 4000 t/d 25 000 t/d ∑ 500 km 4000 t/d 25 000 t/d Offshore pipeline ∑ 500 km 4000 t/d 25 000 t/d Ship ∑ 500 km 4000 t/d 25 000 t/d Levelized cost $/tCO2 Cost of CO2 capture 29–51 37–74 13–37 2–8 30 Total installed capital cost $28 million ($280 000/km) $55 million ($550 000/km) 2.6 0.8 $130 million ($260 000/km) $260 million ($520 000/km) 12.5 4.0 $335 million ($710 000/km) 36 $680 million ($1 360 000/km) 11 $360 million $970 million CO2 injection1 ∑ Injection wells 1000 m 3000 m ∑ Deep saline aquifer 4000 t/d 25 000 t/d ∑ Depleted gas reservoir 4000 t/d 25 000 t/d ∑ Enhanced gas recovery 4000 t/d 25 000 t/d ∑ Enhanced oil recovery 4000 t/d 25 000 t/d ∑ Enhanced coalbed methane 4000 t/d 25 000 t/d 43 23 $420 000/well $2 700 000/well $17–20 million $81–102 million 1.8–2 1.4–1.7 $1–7 million $5–44 million 0.2–1.4 0.2–1.4 $22–172 million $140–1100 million –11 to –8 –11 to –8 $175–513 million $1100–3200 million –14 to –6 –14 to –6 $54–348 million $336–2200 million –12 to 26 –12 to 26 Monitoring 0.2 1 Injection costs are based on reference cases in Section 2.4, but could be much larger or smaller depending on reservoir characteristics and, in the case of enhanced fossil fuel recovery, oil/gas prices. © Woodhead Publishing Limited, 2010 58 Developments and innovation in CCS technology system with CCS in the state of Ohio is illustrated in Fig. 2.11 (Johnson et al., 2008). Beginning with a GIS database, locations of demand (large polygons), coal plant locations (white/black circles), and rights of way are indentified. From this, a set of possible pathways between demand centers (cities) and coal plants is found (Fig. 2.11a), and mathematical programming techniques are used to select the spatially optimal (lowest cost) supply network (Fig. 2.11b). A build-out scenario is postulated, assuming an introduction rate for hydrogen vehicles. In Figure 2.12, we show the growth of the network as the hydrogen demand rises from 5 % of vehicles to 75 %. A more extensive hydrogen pipeline network and more coal to hydrogen plants are added as (a) (b) 2.11 Coal-based hydrogen system optimization with CCS (a) shortest distance pathways between all coal plants and design centres; (b) optimal hydrogen pipeline network (Johnson et al., 2008). (a) Pipeline (b) Interstate Coal plant Intercity station (c) Sequestration site Demand center 2.12 Build-out scenario for coal-based hydrogen system with CCS (a) 5%; (b) 25%; (c) 75% (Johnson et al., 2008). © Woodhead Publishing Limited, 2010 Techno-economic analysis and modeling 59 demand grows. In this study, the hydrogen delivery system (an extensive network of pipelines from the power plant to hydrogen refuelling stations) is found to be a major cost factor. By comparison, the pipeline system for transporting CO2 is relatively small since power plants are located near good sequestration sites. Finally, models of CCS systems have been incorporated into larger models of the energy economy. In these models, various energy supply options compete to supply specified demands for energy services such as lighting, cooling, and transportation. These models yield insight into the potential role of fossil energy systems with CCS under different technology assumptions or policy constraints. A recent study by the IEA (2008) used the MARKAL energy/economics model to examine the potential role of various technologies in reaching low-carbon futures by 2050. Two future scenarios with deep carbon emissions cuts were explored (the ACT Map and BLUE Map Scenarios). They find that coal with CCS plays a major role in meeting a goal of reducing energy-related carbon emissions by 50 % compared to a business as usual scenario. As shown in Fig. 2.13, 14–19 % of the emissions reduction is due to use of CCS in fossil power plants, industry, and fuel production. CO2 capture and sequestration is seen as a critical technology for meeting future climate goals. 2.6 Future trends Models for fossil energy systems with CCS have been developed at the individual component and system level. There remain many uncertainties in the inputs to such models and in the equations themselves, especially those governing injection and storage in underground reservoirs. In the future, as there is more experience with building and operating CCS systems, the uncertainties in cost and performance of power plants, fuel production systems, and industrial plants with CCS should decline and cost estimation should become more accurate. This is important as CO2 capture is the single largest cost associated with a CCS system. Another major source of uncertainty in current cost models is the need to better understand how CO2 behaves in underground storage reservoirs over a period of time. Characterization of reservoirs to estimate injectivity and storage capacity a priori is an active area of research. Progress in this area will improve the quality of cost models for injection sites. The design of a fossil energy system with CCS is regionally dependent. In recent years, several studies have made use of GIS-based data sets to design CO2 pipeline systems in realistic regional case studies. Similar techniques are used to design and route conventional oil and gas pipelines and are proving useful for understanding the possibilities for locating CO2 pipelines. In addition, they allow development of CCS system designs that © Woodhead Publishing Limited, 2010 60 BLUE Map 48 Gt CO2 reduction ACT Map 35 Gt CO2 reduction Nuclear, 6 % © Woodhead Publishing Limited, 2010 CCS power, 8% Power fossil fuel switching and efficiency, 17 % End-use fuel switching, 3 % Nuclear, 6 % CCS industry and transformation, 9% Hydrogen FCVs, 4 % Power fossil fuel switching and efficiency, 7 % End-use fuel switching, 3% CCS power, 10 % End-use fuel efficiency, 24 % End-use fuel efficiency, 28 % Total renewables, 16 % Electrification, 2% Electricity enduse efficiency, 16 % Total renewables, 21 % Electrification, 6% Electricity enduse efficiency, 12 % 2.13 Reduction in CO2 emissions for the ACT Map and BLUE Map scenarios relative to the Baseline scenario by technology area, 2050 (FCV = fuel cell vehicle) (IEA, 2008). 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