Program for North American Mobility In Higher Education
PIECE
MODULE 14. “Life Cycle Assessment (LCA)”
4 steps of LCA, approaches, software, databases,
subjectivity, sensitivity analysis, application to a
classic example.
NAMP
PIECE
Tier III
Open-ended problem
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Prerequisites for tier
What are the prerequisites for this tier?
It is further assumed that students already have an introductory-
level background in Life Cycle Assessment (LCA) (from Tier I and
Tier II) and the basic knowledge in petrochemical processes, such
as would normally be part of any undergraduate engineering
curriculum.
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Statement of intent
What is the purpose of this module?
Open-Ended Design Problem. Is comprised of an openended problem to solve real-life application of LCA to
the oil and gas sector. The global aim of that problem is
to quantify the total environmental benefits and
drawback of a process.
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References
Spath and Mann. (2001) ”Life Cycle Assessment of Hydrogen Production via
Natural Gas Steam Reforming“. National Renewable Energy Laboratory.
 Spath
and Mann. (1999) “Life Cycle Assessment of Coal-fired Power
Production”. National Renewable Energy Laboratory.
Mann and Spath. (1997) “Life Cycle Assessment of Biomass Gasification
Combined-Cycle System”. National Renewable Energy Laboratory.
Rojey A., Minkkinen A., Arlie J.P. and Lebas E. “Combined Production of
Hydrogen, Clean Power and Quality Fuels”. Institut Français du Pétrole (IFP).
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References
D. Gray, G. Tomlinson, “Opportunities For Petroleum Coke Gasification Under Tighter
Sulfur Limits For Transportation Fuels,” Presented at the Gasification Technologies
Conference, San Francisco, California, October 8–11, 2000
H. Baumann, A.M. Tillman(2004). ‘’The hitch Hicker’s Guide to LCA. An orientation in life
cycle assessment methodology and application’’. Studentlitteratur AB. Lund, Sweden
 The Environmental Foundation Bellona : http://www.bellona.no/en/energy
 University of Newbrunswick (Canada) (Petroleum and Natural Gas Processing):
http://www.unb.ca/che/che5134/smr.htm
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Tier III: Content
Tier III is broken in six parts:
•
•
•
•
•
•
Description of the context: Hydrogen production via natural gas
steam reforming
Problem statement
Statement of the intent
Report Structure
Recommendations
Index
Unlike the previous two sections, this section does not have a
quiz. The student must interpret the results of the above work
and elaborate a succinct project report (15 - 20 pages).
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Tier III: Units of measur
Metric units of measure are used. Therefore, material consumption is reported in
units based on the gram (e.g., kilogram or metric tonne), energy consumption
based on the joule (e.g., kilojoule or megajoule), and distance based on the
meter (e.g., meter). When it can contribute to the understanding of the analysis, the
English system equivalent is stated in parenthesis. The metric units used for each
parameter are given below, with the corresponding conversion to English units.
Mass:
kilogram (kg) = 2.205 pounds
Metric tonne (T) = 1.102 ton (t)
Distance: Meter (m) = 6200 mile = 3281 feet
Area:
hectare (ha) = 10,000 m2 = 2.47 acres
Volume:
cubic meter (m3) = 264.17 gallons
normal cubic meters (Nm3) = 0.02628 standard cubic feet (scf) at a standard
temperature & pressure of 15.6°C (60°F) and 101.4 kPa (14.7 psi),
respectively
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Tier III: Units of measur
Pressure:
kilopascals (kPa) = 0.145 pounds per square inch
Energy:
kilojoule (kJ) = 1,000 Joules (J) = 0.9488 Btu
Gigajoule (GJ) = 0.9488 MMBtu (million Btu)
Terajoule (Tj) = 1.0 x 109 Joules (J)
kilowatt-hour (kWh) = 3,414.7 Btu
Gigawatt-hour (GWh) = 3.4 x 109 Btu
Power:
megawatt (MW) = 1 x 106 J/s
Temperature:
°C = (°F - 32)/1.8
Hydrogen Equivalents:
1 kg H2 = 423.3 scf gas = 11.126 Nm3 gas
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Tier III: Abbreviations and Te
Btu CO2-equivalenceEIA GWP HHV HTS IPCCkWh LCA LHV LTS MMSFCD MW N2O Nm3 NMHCs NOx NREL PSA SMR SOx Stressor Stressor category wt% -
British thermal units
Expression of the GWP in terms of CO2 for the following three
components CO2, CH4, N2O, based on IPCC weighting factors
Energy Information Administration
global warming potential
higher heating value
high temperature shift
Intergovernmental Panel on Climate Change
kilowatt-hour (denotes energy)
life cycle assessment
lower heating value
low temperature shift
million standard cubic feet per day
megawatt (denotes power)
nitrous oxide
normal cubic meters
non-methane hydrocarbons
nitrogen oxides, excluding nitrous oxide (N2O)
National Renewable Energy Laboratory
pressure swing adsorption
steam methane reforming
sulfur oxides, including the most common form of airborne sulfur, SO2
A term that collectively defines emissions, resource consumption, and
energy use; a substance or activity that results in a change to the
natural environment
A group of stressors that defines possible impacts
percentage by weight
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Tier III: Outline
1. Description of the context: Hydrogen production via natural gas steam
reforming
2. Problem statement
3. Statement of the intent
a. System boundaries
b. Major assumptions
c. Data
4. Report Structure
5. Recommandations
6. Index
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Tier III: Outline
1.
Description of the context: Hydrogen production via natural gas steam reforming
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1.
Description of the context: Hydrogen production
via natural gas steam reforming
1.1. Hydrogen (H2)
Hydrogen is used in a number of industrial applications, with today’s largest consumers
being ammonia production facilities (40.3 %), oil refineries (37.3%), and methanol
production plants (10.0%). Because such large quantities of hydrogen are required in
these instances, the hydrogen is generally produced by the consumer, and the most
common method is steam reforming of natural gas. The figure below shows a
simplified flowsheet of the process utilised in this context for hydrogen production.
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1.
Description of the context: Hydrogen production
via natural gas steam reforming
1.2. The process
Hydrogen can be produced from natural gas, oil or coal. Synthesis gas production is a
key step, as it gives access to a wide range of options. Synthesis gas which is formed
mainly by a mixture of CO and H2 is obtained either by steam-reforming, in the case of
natural gas or by partial oxidation. Steam methane reforming is the most common and
least expensive method of producing hydrogen. About half of the world's hydrogen is
produced from SMR (Gaudernack, 1998). The process can be used also with other
light hydrocarbon feedstocks, such as ethane and naphtha. The process is endothermic
and synthesis gas is typically produced in a tubular reformer furnace.
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1.
Description of the context: Hydrogen production
via natural gas steam reforming
Inlet temperatures are within the range 450-650°C and the product gas leaves the
reformer at 700-950°C, depending on the applications (Rostrup-Nielsen, 1993). The
desulphurized feedstock is mixed with process steam and reacted over a nickel based
catalyst contained in high alloy steel tubes. Although the plant requires some stream
for the reforming and shift reactions, the highly exothermic reactions results in an
excess amount of steam produced by the plant.
Due to the high operating
temperature in the reformer, the reformer effluent contains about 10-15 vol % CO (dry
basis).
A high-temperature shift (HTS) operating at an inlet temperature of 343 to 371°C
makes possible to convert about 80 to 90% of the CO. This step uses a catalyst which
is typically composed of copper oxide-zinc oxide on alumina. A Pressure Swing
Adsorption unit (PSA) is used for removing CO and other contaminants present with
hydrogen.
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1.
Description of the context: Hydrogen production
via natural gas steam reforming
If the CO2 which is present typically at the level of 15-20% has to be recovered, it may
be more appropriate to use a specific step for separating CO2 from hydrogen by
solvent scrubbing. An amine solvent is typically used for such a separation step. The
hydrogen thus obtained, can be exported. Refining is presently the main consumer of
hydrogen. It can be used also in a combined cycle for generating electricity.
Such a scheme provides therefore an attractive option for producing electricity, without
emitting CO2. Synthesis gas produced during the initial step, can also be used for
producing liquid hydrocarbon fuels, through Fischer-Tropsch synthesis. Thus, it is
possible to transform any fossil fuel or biomass into hydrogen, electricity and liquid
fuels.
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Tier III: Outline
1.
2.
Description of the context: Hydrogen production via natural gas steam reforming
Problem statement
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2.
Problem Statement
An oil & gas plant seeks to modernize by looking at 3 process options: improving the
environmental aspects, improving the performance of some units of production to
maximize the hydrogen production and finaly to install a better system of electronic
control of the process. Your are the process engineer in this firm. Your boss, the plant
manager, wants you to do a study on the the total environmental aspects
(quantification and analysis) of producing 48 MMscfd of hydrogen via natural gas
steam reforming for the intern study. In recognition of the fact that upstream
processes required for the operation of the Steam Methane Reforming (SMR) plant also
produce pollutant and consume energy and natural resources.
The data colletion and validation have already been done by another engineer.
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Tier III: Outline
1.
2.
3.
Description of the context: Hydrogen production via natural gas steam reforming
Problem statement
Statement of the intent
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Tier III: Outline
1.
2.
3.
Description of the context: Hydrogen production via natural gas steam reforming
Problem statement
Statement of the intent
a. System boundaries
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3.
Statement of the intent
3.1. System boundaries
This LCA should be performed in a cradle-to-grave manner, for this reason, natural gas
production and distribution, as well as electricity generation, were included in the
system boundaries. The steps associated with obtaining the natural gas feedstock are
drilling/extraction, processing, and pipeline transport. The next figure shows the
System Boundaries for Hydrogen Production via Natural Gas Steam Reforming.
RM
E
E
Raw
Raw material
material
extraction
extraction
Em
RM
RM
Construction
Construction
of
of equipment
equipment
Production
Production
&
& distribution
distribution
of
of electricity
electricity
RM
Em
E
Recycling
Recycling
Em
Production
Production
&
& distribution
distribution
of
of natural
natural gas
gas
-E
Hydrogen
Hydrogen
production
production
plant
plant
-RM
-Em
Natural
Natural gas
gas
boiler
boiler
x x x x
X -Em
X
E
M
Module 14 – Life Cycle Assessment
RM
Em
E
E = energy
Em = emissions
M = materials
RM = raw materials
Landfilling
Landfilling
Em
E
Em
E
RM
Em
Production
Production
&
& distribution
distribution
of
of natural
natural gas
gas
-E
-RM
Avoided operations
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3.
Statement of the intent
3.1. System boundaries
For this study, the plant life was set at 20 years with 2 years of construction. In year
one, the hydrogen plant begins to operate; plant construction takes place in the two
years prior to this (years negative two and negative one). In year one the hydrogen
plant is assumed to operate only 45% (50% of 90%) of the time due to start-up
activities. In years one through 19, normal plant operation occurs, with a 90% capacity
factor. During the last year the hydrogen plant is decommissioned. Therefore, the
hydrogen plant will be in operation 67.5% (75% of 90%) of the last year.
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Tier III: Outline
1.
2.
3.
Description of the context: Hydrogen production via natural gas steam reforming
Problem statement
Statement of the intent
a. System boundaries
b. Major assumptions
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3.
Statement of the intent
3.2. Major assumptions
A pretreatment on the natural gas is necessary to avoid emposoinment of the catalysts
with the sulphur. The H2S is removed in a hydrogenation reactor and then in a ZnO
bed. After pretreatment, the natural gas and 2.6 MPa steam are fed to the steam
reformer. The resulting synthesis gas is then fed to high temperature shift (HTS) and
LTS reactors where the water gas shift reaction converts 92% of the CO into H2.
Hydrogen Plant Block Flow Diagram
H2 product slipstream
steam
Natural
Hydrogenation
gas
feedstock
ZnO Bed
Catalytic
Steam
Reforming
High
Temperature
Shift
Low
Temperature
Shift
Pressure
Swing
Adsorption H2
Off-gas
Natural
gas fuel
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3.
Statement of the intent
The hydrogen is purified (to 99.9% mol.) using a pressure swing adsorption (PSA)
unit. The reformer is fueled primarily by the PSA off-gas, but a small amount of
natural gas is used to supply the balance of the reformer duty. The PSA off-gas is
comprised of CO2 (47.06 mol%), H2 (24.26 mol%), CH4 (19.59 mol%), CO (7.8
mol%), N2 (0.55 mol%), and some water vapor. The steam reforming process
produces 4.8 MPa steam. Electricity is purchased from the grid to operate the pumps
and compressors.
The hydrogen plant energy efficiency is defined as the total energy produced by
hydrogen plant divided by the total energy into the plant, determines by the following
formula:
energy in product hydrogen  4.8 MPa steam energy (ex ported )
natural gas energy  electricity  2.6 MPa steam energy (required )
The base case of this analysis assumed that 1.4% of the natural gas that is produced
is lost to the atmosphere due to fugitive emissions.
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Tier III: Outline
1.
2.
3.
Description of the context: Hydrogen production via natural gas steam reforming
Problem statement
Statement of the intent
a. System boundaries
b. Major assumptions
c. Data

Construction material Requirement
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3.
Statement of the intent
3.4.1. Construction material requirement:
Construction Plant Materials Requirements
and pipeline
The next table list materials requirements used for the plant in this study. A sensitivity
analysis was performed how changing these numbers would affect the results.
Hydrogen Plant Material Requirement (Base Case)
Material
Amount required
(Mg)
Concrete
9504.6
Steel
3036.4
Aluminum
25.06
Iron
37.12
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3.
Statement of the intent
To move the natural gas from the oil or gas wells to the hydrogen plant, we use
pipelines. Because the main pipeline is shared by many users, only a portion of the
material requirement was allocated for the natural gas combined-cycle plant. For this
analysis, the total length of pipeline transport for the natural gas combined-cycle plant
is assumed to be 425 km, it was sized so that the total pressure drop in the pipe is of
0.05 psi/100 feet (0.001 MPa/100 meters). The pipe has a diameter of 31 inches
assuming a wall thickness of 1 inch. The steel used for the pipe construction has a
density of 7700 kg/m3.
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3.
Statement of the intent
3.4.1. Air Emissions due to materials’ construction
Air emissions due to the plant construction
Air emission
Benzene(C6H6)
g of emission/Kg of H2
produced
1.4
CO2
1614.3
CO
5.46
CH4
50.3
NO2
6.86
N2O
0.0150
NMHCs
15.08
Particulate
0.504
SO2
6.48
The
construction
of
materials
requirements also produce a lot of air
emissions. Because of lack of data, we
will suppose that those constructions emit
2.8652 ton of particulate/hectare of the
mill/month of activity.
You can suppose that NMHCs = 50% mass. benzene + 50% mass. Toluene.
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Tier III: Outline
1.
2.
3.
Description of the context: Hydrogen production via natural gas steam reforming
Problem statement
Statement of the intent
a. System boundaries
b. Major assumptions
c. Data


Construction material Requirement
Natural gas composition and lost
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3.
Statement of the intent
3.4.2. Natural gas composition and loss
While natural gas is generally though of as methane, about 5-25% of the volume is
comprised of ethane, propane, butane, hydrogen sulfide, and inerts (nitrogen, CO2 and
helium). The relative amounts of these components can vary greatly depending on the
location of the wellhead. The next table gives the composition of the natural gas
feedstock use in this analysis, as well as typical pipeline and wellhead compositions.
The composition used in this study (first column) assumes that the natural gas has
undergo a pretreatment before entering the desulphurization reactor. The natural gas
feedstock contains up to 7 ppmv total sulfur, max. 5 ppmv in the form of hydrogen
sulphide (H2S) and max. 2 ppmv organic sulfur as mercaptane.
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3.
Statement of the intent
Natural Gas Composition
Natural gas feedstock used in
analysis
Component
Typical range of wellhead components
(mol%)
Mol % (dry)
Low value
High value
Methane (CH4)
83.59
75
99
Ethane (C2H6)
10.19
1
15
Propane (C3H8)
1.15
1
10
Nitrogen (N2)
1.00
0
15
Carbon Dioxide (CO2)
0.78
0
10
Iso-butane (C4H10)
0.11
0
1
N-butane (C4H10)
0.17
0
2
Pentanes (C5+)
0.04
0
1
N-pentane
0.03
0
----
N- +(C6)
0.03
0
----
Hydrogen (H2)
2.91
0
----
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3.
Statement of the intent
In extracting, process, transmitting, storing and distributing natural gas, some is lost to
the atmosphere. Over the past two decades, the natural gas industry and others have
tried to better quantify the losses. There is a general consensus that fugitive emissions
are the largest source, accounting for about 38% of the total, and that nearly 90% of
the fugitive emissions are a result of leaking compressor components. The second
largest source of methane emissions comes from pneumatic control devices,
accounting for approximately 20% of the total losses.
The majority of the pneumatic losses happen during the extraction step. Engine
exhaust is the third largest source of methane emissions due to incomplete combustion
in reciprocating engines and turbines used in moving the natural gas through the
pipeline. These three sources make up nearly 75 % of the overall estimated methane
emissions. The remaining 25% come from sources such as dehydrators, purging of
transmissions/storage equipment, and meter and pressure regulating stations in
distribution lines.
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Tier III: Outline
1. Description of the context: Hydrogen production via natural gas steam
reforming
2. Problem statement
3. Statement of the intent
a. System boundaries
b. Major assumptions
c. Data
 Construction material Requirement
 Natural gas composition and lost
 Production and distribution of electricity
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3.
Statement of the intent
3.4.3. production and distribution of electricity
Electricity is purchased from the grid to operate the pumps and compressors. The
production was assumed to be the generation mix of coal, lignite (hard coal), oil and
fuel/natural gas. The process consume approx. 129,104 Mj/day. Each fuel provide
respectively 3%, 2%, 72% and 23% of the total energy needed by the process. The
stressors associated with this mix should also determined in a cradle-to-grave manner.
The table below presents the quantity (in kg) of air emissions for each fossil fuel used
for electricity production. Those data relate to a functional unit of 1 Tj net electricity
delivered from the power plant.
Coal
Fuel gas
Oil
Lignite
CO2
275833
245831
229380
370979
CO
56.6
81.97
75.15
45.1
NOx
451.7
408.44
488
12.6
SO2
1062.07
58.29
2359.4
3623.53
Particulates
321.59
16.13
96.87
257.66
N2O
1.79
1.5
5.53
1.8
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Tier III: Outline
1.
2.
3.
Description of the context: Hydrogen production via natural gas steam reforming
Problem statement
Statement of the intent
a. System boundaries
b. Major assumptions
c. Data




Construction material Requirement
Natural gas composition and lost
Production and distribution of electricity
H2 Production plant
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3.
Statement of the intent
3.4.4. H2 Production plant
Hydrogenation and Desulphurization
As the reformer catalyst is sensitive to poisoning from sulfur, sulfur in the natural gasis
processed in a Hydrogenation Reactor. Sulfur is totaly converted to hydrogen sulfide in
this Hydrogenation reactor and will be absorbed on the zinc oxide by conversion of
ZnO to ZnS in the desulphurization reactor. Natural gas leaving the reactor will have a
residual sulfur content of less than 0.2 ppmv.
The total adsorption capacity of the desulphurization catalyst, based on total 7 ppmv
sulfur in the feedstock will be for minimum 2 years of uninterrupted operation.
A small amount of hydrogen, which is recycled from the product stream, is used in the
Hydrogenation step to adjust the pressure in the reactor. The table below gives the
caractheristics of the inflow of the hydrogenation reactor.
Inflows to the hydrogenation reactor
The flow in
Natural gas feedstock
Hydrogen (H2)
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Kg/h
Kmol/h
17222
962
57
28
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3.
Statement of the intent
3.4.4. H2 Production plant
Steam reforming
In the steam reforming, the mixture of desulphurized natural gas and process steam
(3358 kmol/h at 2.6 MPa (380 psi)) is reformed under application or external heat.
The principle chemical reactions taking place in the steam reformer are as follows:
Steam reforming
Cn H m  nH 2O  nCO  (n  m / 2) H 2  heat
Water-gas Shift reaction (which is highly exothermic)
CO  H 2O  CO2  H 2  heat
The effluent contains besides the products CO2 and residual CH4 and H2O. The
reformed gas leaves the SR at 810ºC and approx. 25 kg/cm2 abs.. All reactions take
place simultaneously at about 560ºC. However, the reaction as a whole is endothermic.
Those reactions take place over a nickel-based catalyst.
The waste heat contained in the furnace flue gas is utilized for superheating of the
reformer feedstock, generating of medium pressure steam, superheating of the
medium pressure steam and preheating of the combustion air. Those gases leave the
reformer at approx. 1000ºC.
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3.
Statement of the intent
The reformed gas composition
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Components
% mol.
CO2
6.2
H2
43.73
N2
0.16
C1
4.75
C2
0
C3
0
i-C4
0
N-C4
0
i-C5
0
N-C5
0
N-C6
0
H2O
38.07
CO
7.08
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3.
Statement of the intent
The combustion air given is based on 5% excess air and enters the burner at 380ºC
and approx. 1.2 kg/cm2, at a rate of 123488 kg/h. It is composed of 20.4% mol. O2,
76.77% mol. N2 and 2.83% of H2O.
Waste heat is recovered from the flue gas as well as from the reformed gas to preheat
and superheat process streams and for steam production.
The natural gas utilized as fuel for the burner contains 5 ppmv of H2S and 2 ppmv of
mercaptane and has the following composition and characteristics:
Molar mass (kg/mol)
18.38
Flow in kmol/h
26.4
Pression (kg/cm2)
2
Temperature (ºC)
20
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Statement of the intent
Molar composition of of the natural gas used in the burner
Components
% mol.
CO2
0.8
N2
1.02
C1
86.1
C2
10.5
C3
1.18
i-C4
0.11
N-C4
0.17
i-C5
0.04
N-C5
0.04
N-C6
0.04
Module 14 – Life Cycle Assessment
The table below presents the
composition of the flue gas at the
outlet of the burners.
Components
% mol.
CO2
19.28
O2
1.05
N2
60.28
H2O
19.38
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3.
Statement of the intent
3.4.4. H2 Production plant
High Temperature Shift (HTS)
The carbon monoxide, which is produced in the steam reformer, is converted by
means of water vapor on a catalyst in a HTS reactor to hydrogen and carbon dioxide,
according to the following reaction:
CO  H 2O  CO2  H 2  heat
This reaction is highly exothermic, which leads to temperature rise of about 50ºC. The
CO-content at the outlet of the Shift reactor is less than 2 mol-%. Subsequently the
shifted gas is cooled down in different exchangers to approx. 36ºC. Process
condensate is separated in multiple liquid-gas separators. The gas is then routed to
the PSA Unit.
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3.
Statement of the intent
3.4.4. H2 Production plant
Separators
The outflow gas from the HTS passes by different exchangers and liquid-gas
separators. At the outlet of the last separator, we obtain two flows. On flow of 481
kg/h of liquid water at 35ºC and a gaseous flow principally composed of hydrogen
(H2) and carbon dioxide (CO2) at a rate of 43186 kg/h (3945 kmol/h). The table
bellow gives the molar composition of this gaseous flow:
Molar composition of the gaseous outflow of the last
separator before the PSA unit
Component
Module 14 – Life Cycle Assessment
% mol.
CO2
16.92
CO
2.8
H2
72.7
H2O
0.27
N2
0.24
CH4
7.07
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3.
Statement of the intent
3.4.4. H2 Production plant
Pressure Swing absorption (PSA)
For final purification a Pressure Swing Adsorption process is used. The reminder of
undesired components are removed from the bulk of hydrogen by means of
adsorption on molecular sieves using a PSA. The purification of hydrogen is based on
selective adsorption of gas components such as CH4, CO, CO2, N2 and H2O.
Hydrogen does not absorb and leaves the PSA unit as a product gas with high purity.
Subsequently the pure hydrogen product is compressed and a small amount is
recycled to upstream of the Hydrogenation Reactor.
The adsorbed gases in the PSA are released and routed as off-gases to the off gas
which ensures a stable and constant supply of fuel gas to the burners of the reformer.
The Hydrogen (H2) obtained from the PSA has a 99% molar purity. It leaves the PSA
Unit at 40ºC at 5149 kg/h (2525 kmol/h).
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3.
Statement of the intent
3.4.4. H2 Production plant
Steam Generation System
Waste heat from the process is utilized for steam generation. As the main source of
energy, the sensible heat of the reformed gas downstream Steam Reformer is used for
steam production in Reformed Gas Waste Heat Boiler. An other source of heat for
steam generation is the waste heat of the flue gas leaving the steam reformer. Here
additional steam is produced in Flue Gas Waste Heat Boiler.
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3.
Statement of the intent
3.4.4. H2 Production plant
Shut down
The process is shuted down for 24 hours every 2 years to change the catalysts.
During start-up of the process or PSA Unit failure, we use a burners’ fuel (for the SR)
composed in majority of natural gas (12.88 the mole rate of the natural gas used in
normal operation case) completed with Raffinery fuel. The mole ratio of thoses two
fuels is 8.5.
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Tier III: Outline
1.
2.
3.
4.
Description of the context: Hydrogen production via natural gas steam reforming
Problem statement
Statement of the intent
a. System boundaries
b. Major assumptions
c. Data
Report structure
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4.
Report structure
4.1. Questions for discussion
1- Quantify the environmental loads - resource use and pollutant air emissions - of
the system.
2- Make the results more environmentally relevant by translating the emissions using
environmental themes method. Identify and evaluate the environmental impacts of
the process by making an impact assessment by calculating the total impact. The
index list is in the Index towards the end of the problem.
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4.
Report structure
4.1. Questions for discussion
3- Make a sensitivity study and identify the most important parameters toward their
influence on the results of this study.
4- Examine the net emission of greenhouse gases, as well as the major environmental
consequences.
5- Substitutions scenarios: What possible improvements on the system could we do ?
7- Make a cost-benefit Analysis, typically involves an economic ROI study.
8- Since Risk is another matter not dealt with in LCA, we won’t ask you about it but
you should write a short paragraph about the Ecological Risk Assessment (ERA) related
to this process.
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4.
Report structure
4.2. Suggestion for Report Table of Contents
1.
2.
3.
4.
5.
6.
7.
8.
Executive summury
Introduction
Objectives
Summury of results
Sensitivity Analysis
Impact Assessment
Impovement Opportunities
Conclusions
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Tier III: Outline
1.
2.
3.
4.
5.
Description of the context: Hydrogen production via natural gas steam reforming
Problem statement
Statement of the intent
a. System boundaries
b. Major assumptions
c. Data
Report structure
Recommendations
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5.
Recommendations
1. When reporting the final results of your work it is important to
thoroughly describe the methodology used in this analysis. The report
should explicitly define the system analyzed and the boundaries that
were set.
2. All assumptions or decisions made in performing the work should be
clearly explained and reported along side the final results of this project.
3. The results should not be oversimplified solely for the purposes of
presentation.
4. All the environnemental data needed to do this work are given towards
the end of the problem (in the Index).
5. You should respect the international standards for LCA (ISO 1404014043) when performing the different steps of the analyze.
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End of Tier III
•
•
This is the end of Module 14. Please submit your report to your professor for
grading.
We are always interested in suggestions on how to improve the course. You may
contact us at www.namppimodule.org
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INDEX
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Impact
Categories
To meet the needs of this study, categorization and less-is-better approaches have been
taken. The next table summarizes the stressors categories and main stressors from the
natural gas steam reforming, hydrogen production system.
1. Depletion of abiotic resources
Depletion equivalents for abiotic resources,
expressed relative to antimony (Sb) and based
on ultimate reserves.
Substance
Static reserve life (years)
Natural gas
0.0187 kg Sbeq/m3.
Hard coal
0.0134 kg Sbeq/kg
Soft coal
0.00671 kg Sbeq/kg
Fossil energy
4.81 x 10-4 kg Sbeq/Mj
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Impact
Categories
2. Global warming
Global warning potentials for 100
years expressed in relative to CO2
Trace gas
GWP 100 years
(kg CO2 eqv/kg)
CO2
1
CH4
25
N2O
310
NO2
320
3. Acidification
Generic acidification equivalents expressed
relative to SO2 (CML/NOH 1992; in CML 2002)
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Substance
AP (g SO2 eqv/g)
SO2
1
NOx
0.7
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Impact
Categories
4. Photochemical ozone creation potential (contribution to smog)
Photochemical ozone creation potentials (POCPs) for
high NOx background concentrations expressed
relative to ethylene (CML 2002)
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Substance
High NOx POCPs
(kg ethylene/kg)
CO
0.027
NO2
0.028
Methane
0.006
Ethane
0.123
Propane
0.176
N-butane
0.352
N-pentane
0.395
N-C6
0.495
Benzene
0.218
Toluene
0.637
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Impact
Categories
5. Human toxicity
Human toxicity potentiels, HTPinf, for infinite horizon and global scale. The indicators
are expressed relative to 1,4-dichlorobenzene
Substance
HTP for emissions to air
NO2
1.2
SO2
0.096
Benzene
1900
Toluene
0.33
6. Eutrophication
Generic eutrophication equivalents for emissions to air, water and soil. Indicators are
expressed relative to PO3-4 (CML/NOH 1992; CML 2002).
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Substance
(g PO3-4 /g)
PO3-4
1
H3 PO4
0.97
P
3.06
NH3
0.35
NH4+
0.33
N
0.42
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Impacts Associated with Stressor Categories
Impact
Categories
Major Impact
category
H=human health
E=ecological health
Area impacted
L=local (country)
R=regional (state)
G=global
NO
H, E
R, G
CO2, CH4, N2O,
CO and NOx
(indirectly),
water vapor
H, E
R, G
H, E
L, R
NOx, VOCs
H, E
L, R
Acidification precursors
SO2, NOx, CO2
H, E
L, R
Contributors to corrosion
SO2, H2S, H2O
E
L
Other stressors with toxic effects
NMHCs, benzene
H, E
L
Resource depletion
Fossil fuels,
water, minerals
and ores
E
R, G
Solid waste
Catalysts, coal
ash (indirectly),
flue gas clean up
waste (indirectly)
H, E
L, R
Stressors categories
Stressors
Major
Minor
Ozone depletion compounds
Greenhouse
Gases
Climate change
Particulates
Contributors to smog
Photoquemical
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Economic data
Catalysts
The reactor
The catalyst
Desulphurisation
reactor
Zinc Oxide Desulphurisation
Catalyst (ZnODs)
SR
Description
Quantity
(m3)
Price
Zinc Oxide based catalyst
having specific physical and
textural properties blended
with suitable binders in the
form of pellets
16.5
3.5
US/lb
Nickel Based
A nickel based catalyst on
alpha alumina carrier or
calcium aluminate compound
in the form of rings/high
geometric surface rings.
23.6
3.237
US/L
HTS
Copper Oxide-Zinc Oxide on
Alumina
An iron chrome and copper
promoted iron chrome based
catalyst.
36.5
5.198
US/L
Hydrogenation
reactor
---------------------
7.2
-----
---------------------
Due to lack of data, we suppose that all these catalysts have the same density than
water.
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Economic data
Equipment
Equipment
Description/Utility
Quantity
Vessel
For water
1
Compressor
Centrifugal; Emotor; Isentropic; Combustion Air Fan
3
Compressor
Centrifugal; Emotor; Isentropic; Flue gas Fan
2
Compressor
H2 compressor, Reciprocating, Isentropic
2
Drum
Steam condensate
1
Drum
Tank and deaerator
1
Drum
For flare gas
1
Drum
Gas separator
1
Drum
Shifted gas separator
1
Drum
Shifted gas separator
1
Drum
For fuel gas
1
Shell- tube HE
Feed preheater
1
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Economic data
Shell- tube HE
BFW-Preheater
1
Shell- tube HE
Reformed gas final cooler
1
Plate HE
Blow down cooler
1
Air Cooler
Reformed gas air cooler
1
Static Mixer
At the feed
1
Pumps
Centrifugal; team turbine
2
Pumps
Flare condensate; Drum pump
2
Reactor
Hydrogenation with jacket
1
Reactor
Desulphurization, jacket
1
Reactor
HTS
1
Steamturbine
For BFW pump; back-pressure turbine
1
Steamturbine
Turbine for Fluegas Fan; back-pressure turbine
2
TOTAL
25
Also consider that you need 3 feeds for the alimentation and the effluents and that you have
2 purges.
Consider also that we use a Straightline depreciation during 10 years with a resale price of 0$.
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Economic data
H2 price
Gray and Tomlinson (2000) proposed equations to calculate the hydrogen costs based
on the prices of fuels in the world-wide market, in these equations it is assumed that
the value of hydrogen is equal to the cost of producing it from reformation. Based on
this the cost of sale of hydrogen is given by:
Where:
CSH = 0.45•CGN + 0.76
CSH = Cost of Hydrogen Duty ($/MPCSD)
CGN = Cost of Natural Gas ($/MMBtu)
Gray y Tomlinson (2000) also established a simple equation to estimate the cost of the
natural gas in function of the price of petroleum in the world, which is:
Where:
CGN = 0.13•PPM
PPM = Price of the Petrol in the World ($/BBL)
Most of the hydrogen produced at the present time is consumed in its site of
production. When it is sold in the market, to its production cost is added the cost of
liquefying it and of transporting it.
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Economic data
Electricity cost
In order to calculate the cost of the electricity used to produce hydrogen, Gray and
Tomlinson (2000) assumed that the value of the electricity is determined by the cost of
producing it with a advanced plant of combined cycle of natural gas. It was assumed
that the cost of capital of this type of plants is of $494/kw and an amount of specified
energy of 6.396 BTU/KW. Based on these estimations the sale price required of the
electricity it is given by the following equation:
Where:
CEPH = 0.0064•CGN + 0.0116
CEPH = Cost of electricity for produce hydrogen ($/KWh)
...the end.
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