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CONTENTS
Section
Changes shown by ➧
Page
SCOPE .......................................................................................................................................................2
REFERENCES ...........................................................................................................................................2
INTRODUCTION ........................................................................................................................................3
REGULATORY ISSUES ............................................................................................................................................4
General.......................................................................................................................................................................4
Air ...............................................................................................................................................................................4
Water ..........................................................................................................................................................................5
Solid and liquid Waste ................................................................................................................................................5
Site Remediation ........................................................................................................................................................6
Noise ..........................................................................................................................................................................6
EMISSION AND CONTAMINATION SOURCES.......................................................................................6
EMISSION REDUCTION GUIDANCE .......................................................................................................6
GENERAL PRACTICES ............................................................................................................................................6
PROCESS AND EQUIPMENT RECOMMENDATIONS.............................................................................................7
Alkylation ....................................................................................................................................................................7
Amine Treating, Sour Water Stripping, Sulfur Recovery.............................................................................................7
Catalytic Reforming ....................................................................................................................................................8
Caustic Treating .........................................................................................................................................................9
Coking ........................................................................................................................................................................9
Desalting.....................................................................................................................................................................9
Fired Heaters............................................................................................................................................................10
Fluid Catalytic Cracking ............................................................................................................................................10
Hydrogen Manufacture .............................................................................................................................................11
Ketone Dewaxing .....................................................................................................................................................11
MTBE........................................................................................................................................................................11
Process Contact Steam Condensate........................................................................................................................12
Sewers......................................................................................................................................................................12
Tankage....................................................................................................................................................................12
TABLES
Table 1: Approach To Manufacturing Plant Environmental Control...................................................................... 13
Table 2: References To Major Environmental DP Sections................................................................................... 14
Table 3: List Of Major Emission Sources............................................................................................................... 15
Table 4: Types Of Site Contamination................................................................................................................... 16
Table 5: Components Of An Emission Reduction Program.................................................................................... 17
Table 6: Emission Control Guidance ..................................................................................................................... 18
REVISION MEMO
February 2004
Many minor editorial changes and updates
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SCOPE
The Plant Environmental Considerations DP provides an overview of environmental control technology, types of
contamination, and environmental control recommendations for specific process units. References for additional
environmental guidance, including other DP sections, are listed below.
REFERENCES
1.
2.
3.
4.
5.
Highlights of New and Proposed Air Toxics Regulations, EE.3E.91.
Site Remediation Regulatory Review, EE.42E.92
MEFA: Minimum Emissions Facilities Assessment, EE.12E.92
MEFA: Minimum Emissions Facilities Assessment - Phase 2, EE.123E.92
Rittmeyer, Robert W., Waste Minimization–Part 1: Prepare an Effective Pollution Prevention Program, Chemical
Engineering Progress, May 1991, 56–62.
6. Guidelines for Preparing a Cost-Effective Environmental Assessment, 88 ECS2 79, August 26, 1988
7. Responsible Waste Management Practices, Version 2, Environmental Coordinators Network Best Practice,
May 15, 2003
8. No Oil to Sewer Catalog, EE.76E.2002
9. Operations Integrity Management System (OIMS) Elements 3.4, 7.2, Facilities Design and Construction
10. Onsite Process Units, Wastewater Source Load Study, Environmental Control Toolmaking Project, February 21,
1975, by F.A. Devine, et. al., Correspondence no. 50012
11. Urban, D.B, R. R. Goodrich, "Refinery Process Unit Wastewater Load Factors-Final Report," EE.086E.86,
October, 1986
12. Wastewater Management- Preferred Operating Practices, EE. 99E.98
13. Waste Preferred Operating Practices, EE. 82E. 97
14. Environmental Performance Indicators, Exxon Mobil Corporation Manual, 2002 EPI Manual, November, 2002
15. Best Practice for Managing Risk with the use of Third Party Waste Disposal Facilities, Air, Water, Waste
Best Net
16. Environmental Business Planning Web
http://emcorp.na.xom.com/she/corporate/docs/EBP%20Ref%20Guide%20-%20Dec.doc
17. Energetics, Inc. AICHE, US Dept of Energy, "Waste Reduction Priorities in Manufacturing", a DOE/CWRT
Workshop, August 1, 1994
18. F. H Vaughan, J. B. Wilkinson, "Safety and Environmental Procedures for Projects", TMEE 082, EE.72E.98,
Dec. 1998
19. Environmental Procedure for Processing Challenged Crudes Web
http://emre.na.xom.com/waterwst/SRADOCS_s00/ChalCrude/EnvPtc/EnvPtc.htm
20. Global Best Practice for Processing Opportunity Crudes Web
http://emre.na.xom.com/waterwst/SRADOCS_s00/ChalCrude/EnvPtc/REI.htm
21. Refining Project Systems Manual, TMEE 0112, EE.49E.2002, June 2002
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INTRODUCTION
Incorporating environmental considerations into plant operations and project design is essential due to continuously
expanding regulations that affect the petroleum and petrochemical industries. Trends in regulatory requirements are
moving beyond control of gross emissions and discharges, focussing more on targeted constituents and individual
compounds. These regulations cover discharges to the air, water and ground, the generation of noise and odors, and
the remediation of contaminated sites. Worker and community exposure, as well as impact on the environment must
be evaluated as part of project planning and preparation of environmental impact assessments.
In addition to strict adherence to local environmental and health regulations, ExxonMobil has additional guidelines to
assure that corporate environmental policy and operations integrity are considered. In many cases these may be
more restrictive than local regulations. The effects of our plants on the environment play a major role in the public's
perception of our operations. Good community relations is a valuable asset, and attention to plant discharges which
may be of concern plays a major part in maintaining local support.
Good business sense suggests a stepwise approach when
factoring environmental considerations into
manufacturing plant expansions or new projects. The approach is summarized below, with a more complete
description and examples contained in Table 1.
•
Eliminate/Minimize Sources of Emissions or Wastes by using alternative processes/equipment
•
If Wastes/Emissions cannot be eliminated, Recycle or Reduce them
•
If Wastes/Emissions cannot be reduced, Treat them cost-effectively
•
If Wastes cannot be treated, Dispose of them properly
With reference to the ExxonMobil Refining Project System, environmental impacts should be identified and
considered prior to Gate 1 in the business planning stage. A set of possible alternatives should be explored where
environmental impacts are significant. A more extensive evaluation is needed during engineering screening studies
done prior to Gate 2, as facility bases are prepared, compared and cost estimates developed.
It is important that environmental impacts are identified, and alternatives assessed in parallel with economic
considerations. This early assessment within the planning process allows project management to make moreinformed decisions when evaluating project alternatives and their impacts. A team of process and environmental
engineers, along with regulatory compliance specialists should be consulted in the early stages of the project to
identify environmental considerations.
In some cases, operating permits may need to be re-opened and re-negotiated with government authorities. In other
cases, small incremental investments in low emission alternatives can result in large waste reductions or emission
credits. These credits may be used with governmental authorities to gain more flexible operating permits, regulatory
relief in other areas, or intangible, but important public perception credits.
Economic evaluation should consider all costs in the life cycle of the project and net environmental impacts should
be identified. Design Practices XVIII through XX provide details on recommended procedures and control
requirements for specific situations. This section provides an overview of the major environmental regulatory issues,
a listing of emission sources and types of site contamination, and environmental considerations for specific
equipment and process units.
Table 2 may be used as a guide to locate sections containing information on a particular environmental control topic.
Specific technology is arranged by environmental media (e.g. air, water, waste) and key contaminants.
The ExxonMobil Corporation Environmental Performance Indicators (EPI) Manual explains the EPIs that are tracked
from different regions and segments of the business. Examples include effluent water discharge oil and biochemical
oxygen demand (BOD5) in tonnes per year, and a number of air emissions, including VOCs, SOx, NOx and GHGs.
These indicators and corporate targets should be considered when assessing plant environmental facility needs.
The EPIs, and Emission Estimating Guide (EEG) and the guidance manual for Environmental Business Plans are
tools that can be used to assess facility needs at the manufacturing plant.
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REGULATORY ISSUES
General
The environmental laws and regulations which affect ExxonMobil's operations continue to become more stringent and
complicated. These regulations are usually specific to a particular country, state, or province and each location will
have its own unique set of requirements which need to be met. It is of primary importance to be aware of current and
potential environmental laws and regulations in order to maintain compliance and to prepare for future requirements.
Sometimes minor modifications of existing facilities can cause a re-opening of an existing operating permit. In some
cases there is opportunity for negotiation in setting both the quantity and concentration of permitted emissions, or site
clean-up/remediation requirements. A recent trend is for regulators to accept “risk-based” solutions rather than strict
adherence to numerical standards.
Favorable changes in the details and implementation of regulations are
sometimes possible if it can be demonstrated that regulations are unnecessarily excessive based upon human
health considerations, environmental risk assessment (show negative net environmental benefit), and a cost versus
benefit analysis. . In addition, the new trend in regulation is to provide flexibility in achieving goals. This may allow
alternative approaches such as an emission 'bubble' over the entire manufacturing plant, or emissions trading with
other manufacturing plants which result in similar emission reductions at reduced cost, to be considered.
The charter of most environmental regulatory agencies is to provide for the protection of the community, plant
workers, and the environment. Protection levels for the surrounding community and ExxonMobil personnel are
documented in government and industry standards and ExxonMobil Biomedical Sciences (EMBSI) publications.
These allowable levels are periodically revised, and care should be taken in obtaining the latest limits and in their
use. Consultation with the plant Industrial Hygienist (IH) is recommended to clarify appropriate long and short term
personnel exposure limits. In some locations, limits on emissions or clean-up requirements are also set to preserve
the “quality of life". This includes such intangibles as the effects on vegetation and animal species as well as odor and
noise annoyances.
In most locations, there is a need to obtain a “permit or license" before starting construction or as a condition of being
able to operate the facility. These permits usually set out the allowable emissions from the operation and may
document the required equipment deemed necessary for control. Various impact analyses may be required in order
to determine ambient concentrations resulting from plant emissions. The most stringent regulatory agencies are likely
to require risk assessments which fully document emissions to all media and consider combined effects of different
emissions on the surrounding community. These analyses involve emission estimates, dispersion modeling, water
effluent estimates and population density and land use considerations (e.g. schools, health care facilities). For site
remediation, clean-up requirements may be based on fixed regulatory contaminant concentrations or may be derived
from a risk analysis.
Air
There are several different types of emissions to the air which may be a concern. These include the products of
combustion, volatile organic compounds, hazardous air pollutants, and particulate matter. Regulation of combustion
processes has historically focused on the emission quantity and concentration of oxides of sulfur and particulates
based on respiratory concerns. More recently, oxides of nitrogen have received increased attention due to both acid
precipitation and ozone formation. Particulate emissions have also received additional focus due to the heavy metals
which may be present in the particulate phase and the potential effects of fine particulate matter. The ambient
concentration of fine particulate matter (less than 2.5 micron), which is generally emitted in aerosol form from
combustion operations and atmospheric interactions, is now being regulated. The other recent expansion of controls
on combustion emissions relates to the so called “greenhouse" effect (global warming) and limits carbon dioxide and
methane emissions (greenhouse gases).
Controls on the emissions of volatile organic compounds (VOCs) and on air toxics significantly affect facility
operations. In many locations, the concentration of ozone (urban smog) is above health based standards. Although
emissions from mobile sources contribute significantly to these high ozone levels, controls are focused on industrial
sources of VOCs and nitrogen oxides (NOx). Addressing concerns about emissions of air toxics and other potentially
hazardous releases and their effects on the surrounding community is one of the most active regulatory areas. Air
emissions from fugitives (valves, pumps, etc.), tanks, waste water treating, loading operations and vents are receiving
increased attention and, in some locations, controls requiring ninety percent or greater reduction in emissions are
being required. Leak detection and repair programs (LDAR) are becoming prevalent, requiring measurement and
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correction of fugitive emissions. Emissions of polynuclear aromatics (PNAs) and heavy metals on particulates from
sources such as landfarms, unpaved roads and site remediation operations are also receiving increased attention.
Planning for and mitigating the effects of accidental releases of hazardous vapors has been a major focus of recent
regulation. New dispersion models are used to determine the potential affected areas in the result of a spill and also
to evaluate the effectiveness of various controls. Incidental releases of VOCs and toxics are often the cause of
community odor complaints which are sometimes regulated to protect the “quality of life."
There is an increasing trend toward international agreements to address air pollution concerns since in many cases
the effects of emissions are evident large distances from the sources. Reduction of acid precipitation was part of an
agreement between Canada and the United States. More recently, the Montreal Protocol, an international agreement
to halt production of certain chlorofluorocarbons, was negotiated to mitigate the depletion of stratospheric ozone.
Water
Quality requirements for industrial wastewater effluents have changed significantly worldwide since the passing of the
Clean Water Act in the United States in 1975. Past regulations focused on conventional contaminants such as oil and
grease, biochemical oxygen demand (BOD5) and suspended solids (TSS). In many locations, regulatory authorities
are continuing to reduce the allowable concentrations and mass limits of these indicator parameters of pollution. In
these regulations and many others worldwide, additional emphasis is on the control of toxic compounds. Specific
effluent concentration and/or quantity limits are being imposed on industrial facilities for compounds such as
phenolics, benzene, and metals. In many locations regulatory agencies are placing limits on nutrient (nitrogen and
phosphorus) discharges which may cause uncontrolled algae or vegetative growth (eutrification) in receiving bodies
of water. The vegetative growth, if escalated to an undesirable stage, can reduce the intended uses of the water
resource, negatively impact wildlife, change the aesthetic appearance or quality, or increase the cost of pretreating
the water for industrial, domestic or agricultural uses. Regulatory limits for acute and chronic toxicity to aquatic
organisms has become more common, and can affect the selection of WWTP equipment considered in plant design.
Many environmental agencies are requiring more consistent compliance and more frequent monitoring and reporting
for established effluent limits. The capability of new analytical methods to measure very low concentrations is creating
the need for increased emphasis on reducing toxic contaminants. In locations that require maximum water reuse,
concerns focus on avoiding excessive concentration of the contaminants that need to be treated prior to discharge.
Also, new projects are changing the types and quantities of compounds entering the wastewater system. The need
for more consistent compliance has introduced other challenges to the WWTP operation. Sparing philosophy has to
be considered since there will likely be no scheduled WWTP turnaround for a significant period of time, much longer
than typical refinery petroleum process equipment. Therefore, all WWTP equipment has to be designed for removal
from service with part or all of the facility in operation, while continuing to meet all discharge requirements.
New regulations are starting to consider the tendency of certain compounds to bio-accumulate in aquatic organisms.
The protection of larger systems, such as watersheds, is also under regulatory consideration and may require
extensive sampling, analysis and modeling of wastewater effluent discharges into these water bodies.
An understanding of current and projected air emission requirements at the WWTP is essential, as it will impact
treatment plant equipment selection, since certain types of equipment are not amenable to retrofitting to meet more
stringent air emission standards.
Solid and liquid Waste
Until the mid 1970s, solid and liquid waste disposal consisted mainly of biological treatment via landfarms and burial
in landfills. Increasing concerns over protection of human health and the environment have led many countries to
place restrictions on the disposal of these "hazardous" wastes. New regulations have been enacted to protect the
quality of ground and surface waters, the air, and land from contamination by solid waste. Today, in many countries,
biomass is classified as "hazardous or dangerous" waste.
A solid or liquid waste may be deemed hazardous based on its quantity, concentration, physical or chemical
properties . Wastes may be classified as hazardous if they may cause, or significantly contribute to, a substantial
present or potential hazard to human health or the environment when improperly treated, stored, transported, or
disposed. A solid waste is usually classified as hazardous when it exhibits characteristics of ignitability, corrosivity,
reactivity, or toxicity. In many locations, specific manufacturing by–products or process streams have been classified
as hazardous. The definition of hazardous may differ between states, provinces, or countries.
The trend in solid/hazardous waste regulation focuses on the “cradle to grave" concept of hazardous waste
management. This approach involves comprehensive tracking procedures and full documentation of waste
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generation, shipment, storage, treatment and disposal. Several regulatory bodies now limit the transport of hazardous
wastes to other jurisdictions for disposal. ExxonMobil regions and operating affiliates have plans for managing
wastes properly to meet company and government needs. This approach is clearly communicated in OIMS 6.5,
which requires a system be in place to track emissions and wastes, to evaluate pollution prevention steps, and to
control emissions and wastes consistent with policy, regulatory requirements, and business objectives. ExxonMobil
maintains a list of Approved Hazardous Waste Sites, which are periodically audited to ensure that potential liability to
the company is minimized (refer to ExxonMobil Waste Disposal Site Audit List). If certain wastes cannot be accepted
at these audited sites, treatment facilities may need to be installed on-site.
Site Remediation
Regulations covering the remediation of contaminated sites are focused on reducing the volume, toxicity and/or
mobility of the contaminants. These regulations are often focused on protecting groundwater quality. Historically,
regulations have addressed clean-up of current or recent contamination. More recently, regulations mandate the
remediation of older spills, leaks and disposal sites.
Clean-up levels are often fixed by regulation, but may be negotiated based on general guidelines and risk
assessments of site specific conditions. Separate surface and sub–surface clean-up levels may be used, reflecting
different exposure pathways and potential health risks. In most locations, remediation requirements are based on
specific contaminants of concern as well as general parameters such as the total hydrocarbon present. There is a
trend toward setting levels based on risk to humans and ecological receptors. Since many of ExxonMobil
manufacturing facilities have been in operation for over 50 years, project planners need to factor in the cost of
contaminated soil handling and disposal during the construction of new projects or revamp of existing facilities where
soil excavation and removal is planned.
Noise
Regulations to control noise are based on protection from hearing damage as well as mitigating annoyance to
preserve “quality of life." In addition, limits are sometimes set to ensure clear communications in control rooms.
Standards for worker safety have been established and appropriate noise levels for industrial, commercial and
residential areas need to be checked for the particular local jurisdiction. Currently, there are workplace and
community noise limits in most countries.
Noise sources which may be regulated include blowers, gas turbines, fired heaters, construction equipment, motors
and engines as well as intermittent noise sources such as flares, safety relief valves, and other flow induced noise.
Options for controlling the generation of noise and thus mitigating its effects include purchasing low–noise equipment
and installing noise control devices such as enclosures, pipe insulation and silencers.
EMISSION AND CONTAMINATION SOURCES
Table 2 lists the major sources of plant emissions along with the pollutants usually associated with each source.
Table 3 lists the types of site contamination. Air emissions estimating procedures are included in the ExxonMobil
manual at the following website: http://emre.na.xom.com/tmee046/contents_sra/tmee046.htm
EMISSION REDUCTION GUIDANCE
GENERAL PRACTICES
There are usually a number of ways in which emissions of various pollutants can be reduced. In some cases there
are technical limitations, but most often cost is the major consideration. The first part of this section is focused on
reducing the generation of wastes rather than treating or controlling them with “end of pipe" methods. These activities
have been referred to as “pollution prevention" or “source control". The second part of this section provides specific
recommendations for emissions reduction in manufacturing plant operations. A key activity to evaluate emissions
and potential reduction is to prepare a flow sheet and material balance on the particular facility or project under
consideration. Air Emission estimating tools are on the SHE website (http://emcorp.na.xom.com/she/) and in the
Emission Estimating Guide and water/wastewater estimation guidance can be found in the Environmental Design
Practices.
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Table 4 describes a hierarchy of environmental control. At the top of the list is waste minimization and at the bottom
of the list is disposal. In most cases, the preference in cost effective and responsible waste management is to
address emissions using techniques near the top of the hierarchy listing.
The components of an emission reduction program are listed in Table 5. The most cost-efficient time to incorporate
emission reduction opportunities is during process development or facilities design.
In application of emission reduction technologies, the effects on other media should be considered. Sometimes, an
action that results in a reduction of one type of emission results in creating a problem in another media. In general,
the transfer of a pollutant from one media to another doesn't eliminate the problem, but ideally results in a more
technically and economically feasible control alternative. Examples of transfers include the control of air pollutants
that results in the generation of water or solid wastes; removal of wastewater dissolved metals creating a waste
sludge; and disposal of sludge to landfill creating potential liability due to contamination of the ground water or soil.
PROCESS AND EQUIPMENT RECOMMENDATIONS
Table 6 summarizes emission reduction options. Additional details on low emission design considerations and
emission reduction strategies for selected process areas are summarized below. An in–depth discussion of these
concepts is available in references 3 and 4.
Alkylation
Sulfuric Acid Alkylation: From an environmental aspect, a key emission issue from the alky plant is low pH material to
the sewer. Biological treatment systems can be severely affected with an acid spill. Low pH (4 or less) in a BIOX unit
can completely kill the microorganisms used for treatment. Therefore, special precautions must be taken in the
alkylation unit as well as in the sulfuric acid loading and unloading areas. At the alky plant, a neutralization pit is
provided to allow acid or caustic to be added to neutralize what is in the pit before discharge to sewer. The pit should
be designed with reliability in mind. Redundant pH meters should be provided, and corrosion resistant materials must
be used to prevent leakage to the sewer. At loading and unloading areas, a containment sump should be provided in
case of spillage. Fugitive emissions from alky units can be an issue due to use and recovery of isobutane, as well as
the propylene and butylene feedstocks. Alkylation units are provided with their own flare knock-out (KO) drums to
keep acid out of the main refinery flare system. Alkylation plants may include a caustic wash system for propane,
which generates spent caustic. This spent caustic can typically be reused in the WWTP if it is metered in the system
at a controlled rate.
Hydrofluoric (HF) Acid Alkylation: HF alkylation introduces additional concerns over those of sulfuric acid alkylation,
due to the additional safety and IH issues of HF. Fluoride is typically regulated in the WWTP effluent, and lime
addition facilities are typically used to precipitate fluorides from spills and other excursions. While lime can control
effluent fluoride, the calcium added can result in precipitation and scaling in the WWTP primary separation
equipment, and in some cases may result in reliability issues in Dissolved Air Flotation units (DAFs) due to solids
deposition. HF alkylation units also generate sludges which contain fluorides and must be managed responsibly.
Amine Treating, Sour Water Stripping, Sulfur Recovery
In order to limit the sulfur in fuel gas, feedstocks to certain process units, and certain products, refineries remove
hydrogen sulfide by amine scrubbing. MEA (mono-ethanol amine)and DEA (di ethanol amine)are the most common
amines, but other amines are sometimes used. Amine selection can impact air (primarily SOx) emissions from fired
heaters. Amine entrainment from scrubbers, losses from process equipment leaks and excess water purge from
regenerator overhead can all contribute to amine losses. Amine lost will typically end up in the WWTP, and
represents both BOD and organic nitrogen load. Effective amine unit design should always strive to minimize amine
losses, due to the cost of replacing the amines and their impact on the WWTP. Foaming in amine systems creates
major upsets, both in the sulfur recovery unit and in the WWTP. All amine scrubbers should be provided with tower
differential pressure (DP) measurement with high DP alarms in the control center to alert for an amine loss. Oil
skimming facilities should be provided in the regenerator overhead accumulator. The rich amine flash drum should
be provided with reliable oil separation and removal capability, ideally where no amine/hydrocarbon interface
instrumentation is needed (See DP Section V-B). Facilities to inject antifoam at the inlet to the regenerator should be
provided. Activated carbon columns should either be included or stub outs included for future installation. MEA
reclaimers generate a high nitrogen sludge, which must be managed. The sludge can put a heavy load on the
WWTP, and must be considered in the WWTP design. The preferred alternative is to send the reclaimer sludge to a
third party reclaimer or waste disposal site.
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Regeneration of the amine produces an H2S rich gas stream that is routed to the sulfur recovery plant. Sulfur plant
problems can result in diversion of high H2S gas stream to an H2S flare. To minimize odor issues with an acid gas
flare, fuel gas injection facilities into the acid gas flare should be provided to improve H2S combustion. New designs
should provide facilities to minimize use of the acid gas flare for startups and shutdowns.
Sour water streams from many different processes are routed to sour water strippers to remove H2S and NH3. From
an environmental standpoint, it is preferable to use a steam reboiler for heating rather than live steam injection, to
keep stripped sour water volume to a minimum. Fixed valve trays are preferable over sieve trays for better resistance
to fouling and better reliability. Startup and shutdown facilities should include a startup line that recycles effluent back
to the feed tank, feed drum, or slop tankage. This allows time to test the wastewater before sending water to the
WWTP or desalter. For better ammonia removal, consideration should be given to installing a stripper where the
upper section is used for H2S and gross NH3 removal, and the bottom 4-6 trays operate at a higher pH (by injecting
caustic) to achieve 10-15 ppm effluent ammonia levels. Consideration should also be given to provide pH control on
the bottoms from the sour water stripper, since this wastewater is typically reused in the desalter. Lower pH water (pH
6-7) is preferred for use in the desalter to greatly improve oil- water separation and prevent oil undercarry in the
desalter washwater discharge to WWTP.
Sulfur recovery is usually accomplished in a Claus plant. There are some process options which affect recovery, such
as how many reactors to use (typically 3), and whether to use hot gas bypass to heat the reactor inlets or to use fired
reheaters. While hot gas bypass is easier to operate, recoveries are higher with fired reheaters. However, with high
efficiency FLEXSOR tail gas units, the hot gas bypass Claus plant might be more desirable. The off–gas from a
Claus plant, referred to as tail gas, consists of SO2, H2S, CO2, N2 and water vapor. While most locations used to
route tail gas to an incinerator, most locations now route the tail gas to a hydrogenator followed by a tail gas clean-up
unit. The hydrogenator converts all the SO2 to H2S, then the tail gas unit scrubs out the H2S. Essentially all new tail
gas units employ ExxonMobil proprietary Flexsorb technology, where the tail gas is scrubbed by an amine solution,
which is then regenerated, and the H2S off gas is sent back to the sulfur recovery unit. Flexsorb SE technology can
reduce tail gas H2S emissions to less than 5 ppm. It is a very environmentally friendly, totally enclosed system with
very few operating issues, and very minor solvent losses.
Catalytic Reforming
Emissions from reforming can be divided into those from “on–oil" operation and those from catalyst regeneration. The
“on–oil" emissions are mostly hydrocarbons in the form of fugitive emissions, water condensates, and as adsorbed
material on disposed sludges and media from traps, dryers, and adsorbers. The presence of benzene in these
streams increases the need for controls. Emissions which occur during regeneration include hydrocarbons,
combustion products, and chlorine and sulfur compounds. These species can be found in the reactor purges and
scrubber waters, and on spent catalyst, traps, dryers and adsorbers. Some work has shown the potential for very low
trace levels of dioxin emissions from continuous catalytic reforming (CCR)units and not from Powerformers. Hence,
if dioxins are an issue in the particular location, this info may be helpful in identifying the type of reforming unit that
should be considered for the project.
DP XVIII–A2 provides guidance for reducing fugitive emissions. Dealing with the air emissions from the catalyst
regeneration step is sometimes difficult. One option is to precede the inert gas purge with a hot hydrogen sweep to
the fuel gas system or to send the purge stream to the flare or other vapor control. The latter option is likely not to be
an economic alternative.
Primary water emissions during regeneration can be minimized by using hot rather than cold flue gas regeneration. In
the latter, the regeneration gas is scrubbed with water to prevent the recirculation of undesirable chemical species
such as HCl and H2S. Alternatively, hot flue gas regeneration minimizes the formation of condensates, but requires
that the pollutants be controlled as air emissions in a dryer or adsorber. The drier or adsorber will then require
regeneration.
In locations where wastewater streams result from wet scrubbing of the on–oil recycle gas or the use of cold gas
regeneration, the wastewater stream should be kept isolated to minimize the volume of waste water containing
benzene. In some locations, these benzene waste containing streams may need to be treated separately. For the
same reasons, as well as to reduce the load on the wastewater plant, sludge formed in the separator drums should
be kept out of the sewers.
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Caustic Treating
Spent caustic is generated after caustic washing of various streams to remove H2S and mercaptans. When H2S is
the only component, the spent caustic can be used at the WWTP for pH control. Spent caustics containing high
concentrations of mercaptans, cresylic acids and/or naphthenic acids must be handled differently. These caustics
were at one time reused in the pulp and paper industry, but increased regulations have led to essentially no outlets
for spent caustic from refining. MERICHEM (www.merichem.com) used to and still does reclaim spent caustic in their
process at a cost, but those costs have increased dramatically. New projects which generate spent caustic should
carefully evaluate whether a waste will need to be sent out for disposal.
Coking
Fluid and Flexicokers: Cokers are a source of combustion products and sour water. Combustion emissions can be
controlled using standard technology. It is not uncommon to combine off gas from Coking units with FCCU offgas.
Coker offgas contains basically the same contaminants as described later for an FCCU. Coker wet gas is also similar
to FCCU in terms of contaminants and processing requirements. Sour water is generated in Coking units that
contains H2S and NH3, in addition to phenols and thiocyanate. Typically, the sour water is routed to a sour water
stripper. At locations where it is allowable, coker sour water is used as coke quench. If sour water as quench is not
allowed, stripped sour water is an excellent source of quench water, rather than fresh water. Use of stripped sour
water reduces fresh water usage and reduces contaminant load to the WWTP. Coker sour water can also be used to
supplement FCCU circulation water to reduce corrosion in the FCCU. Coke particles, similar to other suspended
solids that enter the refinery sewers generate up to 10 times their weight in wet sludge, which is costly to dispose of.
Sumps at Cokers to collect coke, and coke settling basins or separators, before it gets mixed with other sewer
contaminants should be considered. Coke storage facilities can have particulate emissions, and bag filters are
typically specified to reduce particulate emissions. Truck or rail car loading facilities should also focus on minimizing
particulate emissions. Fluid and Flexicokers are an excellent place to reuse sludges generated in refining. However,
sludge rerun impacts unit capacity, so this should be considered in new designs. Typical sludge generation per 100
kBD of crude capacity is about 150-250 B/D, and additional capacity to handle this should be incorporated into new
coker designs.
Delayed Cokers: Delayed cokers generate a wet gas and sour water. Wet gas and sour water considerations are
the same as Fluid/Flexi cokers and FCCUs. In addition, delayed cokers generate spent water from coke cutting
operations. This water is typically routed to the process sewer, and can contain coke fines. Good design of coke
recovery facilities save sewer cleaning costs later. Sludges are also reused in delayed cokers and new designs
should include facilities to handle the sludge rerun.
Desalting
Crude oil desalters tend to impact wastewater treatment plant operation more frequently than any other piece of
equipment in the refinery. Problems associated with desalting include emulsions, gross free oil, and oily solids. The
proper design and operation of the desalter and brine handling system is imperative for good WWTP operation.
While the purpose of the desalter is to control crude unit overhead corrosion and heater fouling by removing salts
from the crude oil, the brine quality is equally as important as the desalted crude quality.
Crude oil selection flexibility provides a major competitive advantage for any site. However, opportunity crudes make
desalter operation more challenging, and oftentimes the resulting desalter brine quality limits how much of a specific
crude can be processed. Highly water-soluble crude oil contaminants, such as methanol and glycol, partition with the
desalter brine and may pose a concern based on the facility's capacity to handle these contaminants in the WWTP.
More information is available in the Environmental Procedure for Processing Challenged Crudes, described in the
reference section of this document. The Environmental Procedure is part of the Global Best Practice for Processing
Opportunity Crudes, also described in the reference section.
The desalter handbook and Operating Guide (EETD 085) includes many considerations for desalter design,
focussing primarily on maximizing salt removal from the crude. With current trends in crude quality, it is also prudent
to pre-invest for crude that is heavier and more viscous than expected when specifying a desalter.
Listed below are the most important desalter design considerations from a brine quality standpoint:
1.
Page
Use of EMRE mudwash design maximizes water residence time in the desalter, which keeps oil carryunder
to a minimum. This extends desalter runlength to allow uninterrupted operation between turnarounds.
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2.
Use of the three AGAR probe level control design, or the next-generation On-line Water Level (OWL) design
provides maximum desalter level control and allows effective monitoring of emulsion band. Early response
can prevent grid short circuit and/or wide emulsion band, either of which can result massive oil carryunder.
3.
Selection of proper wash water and/or pH control facilities so that desalter brine pH can be maintained at
7.0 or below. Higher pH significantly reduces the coalescing efficiency in the desalter.
4.
Include facilities to add demulsifier and wetting agent , locating demulsifier injection point far from desalter to
allow good contacting.. Wetting agents reduce/prevent buildup of solids stabilized emulsions at the
interface, and also reduce the oil content of the desalter brine solids.
5.
Keep water injection to the preheat train upstream of the desalter to no more than 1% on crude. Excess
water injected can result in more difficult to break emulsions in the desalter.
6.
When specifying the desalter brine handling system, consider that solids in the brine will foul heat exchange
equipment, and contribute significantly to sludge buildup in downstream brine storage or equalization tanks.
7.
For a new desalter, brine oil content should be specified to be less than 250 ppm. Bilectric type desalters,
made by PETRECO have very good oil removal capability.
8.
All desalter control parameters (mix valve, demulsifier injection, level control) should be in the DCS system.
Consistent operation from a manually controlled desalter is not possible.
9.
Consider water reuse options for desalter wash water. Use of stripped sour water can reduce the overall
BOD and phenol load to the WWT because of phenolic compound removal across the desalter (up to 90%
of SWS phenols removed). Use of other process contact condensate can reduce oil levels in the sewer
(See DP Section XIX-B).
Desalter brine contributes a large portion of the total benzene that goes to refinery wastewater treating. In the U.S.,
benzene removal from desalter brine is typically necessary, requiring a benzene stripper or Induced Gas Flotation
unit (IGF). Even at some locations outside the U.S., flotation units have been installed to remove crude solids from
desalter brine before they get to the WWTP. Solids removal from desalter brine significantly improves WWTP
operation.
With the increased concerns about exposure to benzene vapor in workspaces, desalters should be designed to be
effectively cleared prior to entry to avoid need for self contained breathing apparatus. Strategically placed nozzles
can allow circulation of chemicals that will absorb benzene.
Fired Heaters
Fired heaters are being required to use low NOx burners to minimize NOx emissions.. More and more pressure is
being applied to use gas fuel versus liquid fuel because of greater potential for lower emissions. Instrumentation is
typically required which allows furnace heat duty and efficiency to be readily calculated. It is typical to have permit
limits based on furnace heat duty. Furnace SOx emissions are also tightly controlled, but typically managed via fuel
gas treatment for H2S removal. However, SOx emission limits may restrict use of waste gas burners in furnaces if
the waste gas contains significant amount of H2S, mercaptans, or other reduced sulfur species.
Fluid Catalytic Cracking
Air contaminants from fluid catalytic cracking are present in both the reactor product gas and in the regenerator flue
gas. The reactor product gases can be purified by merox processes, caustic washing, and/or amine scrubbing. The
FCCU is usually the largest producer of fuel gas in the refinery. FCCU fuel gas can be high in H2S, CO, COS, and
mercaptans, and is typically treated with amine. A water wash is sometimes installed before the amine scrubber to
remove CO, COS, and other impurities prior to contact with amine. This treating procedure can reduce amine
degradation and improve removal of other reduced sulfur compounds aside from H2S. The source of wash water
could be from wastewater source such as stripped sour waters or pipestill condensate, thus providing a potential
water reuse opportunity.
Regenerator flue gas contains SOx, NOx, CO, CO2 and catalyst fines. There are many control technologies
applicable to reducing emissions of particulates, sulfur oxides, nitrogen oxides, and carbon monoxide. Reduction of
catalyst fine emissions has been achieved through a combination of catalyst physical property enhancements, reactor
design considerations, and changes in operating conditions. Present catalysts are coarser, denser and more attrition
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resistant and have been combined with significant improvements in cyclone design. Equipment for control of
particulate emissions include electrostatic precipitators, fabric filters, and wet scrubbing. Additional details are
available in DP sections XVIII–A3 through XVIII–A6. Approaches to reduce SOx emissions include hydrotreating the
feed, the use of De–SOx transfer additives, flue gas desulfurization, and wet gas scrubbing. SOx emission control
techniques include dry sorbents, and gas scrubbing (dry or wet). NOx emission control methods include selective
non–catalytic reduction (SNCR) (ExxonMobil's Thermal DeNOx Process and urea based reduction processes), and
selective catalytic reduction (SCR). For low temperature (partial burn) regenerators, a CO boiler is used both as a CO
emissions control device and as a steam generator. It has been found operating the regenerator at full burn
(complete conversion of CO to CO2) may result in lower NOx emissions .
The FCCU generates the large majority of sour water in refineries. To control corrosion by cyanide, makeup water is
sometimes added to promote contacting with the gas stream. Ammonium Polysulfide is added to FCCUs to convert
cyanide to thiocyanate. Thiocyanate from FCCU can represent a large non-NH3 nitrogen load to the WWTP. The
FCCU Sour water contains phenolic compounds, H2S, and NH3, and is usually routed to the sour water stripper to
remove NH3 and H2S. The stripped FCCU sour water typically requires biological treatment to reduce the BOD level
prior to discharge.
FCCUs use large amounts of catalyst, and can generate several tons per day of waste catalyst fines when they are
withdrawn. Spent catalyst can sometimes be sold as equilibrium catalyst to another FCCU plant or resid cracker,
sent back to the manufacturer to be reclaimed, or disposed of as a non-hazardous industrial waste. FCCU fines also
settle in the Cat Bottoms stream storage tanks, which need to be periodically cleaned out and generate a waste
sludge. FCCU catalyst from loading/unloading operations can contribute significantly to sewer solids if facilities are
not adequately designed. When these solids enter the sewer and get mixed with other solids, the options for
handling are reduced, costs increase, and sludge volume increases due to increase in moisture content.
Hydrogen Manufacture
Hydrogen plants use steam reforming to produce hydrogen from hydrocarbons. A concentrated CO2 stream is
emitted from hydrogen plants to the atmosphere. An amine solvent is used to remove CO2 from the hydrogen.
Typically catacarb or MDEA is used to scrub the CO2. Catacarb contains Vanadium, which can contribute to the
wastewater effluent, so the amounts must be checked versus permit limits. Both catacarb and MDEA contain organic
nitrogen and BOD load that can overwhelm a WWTP when spilled. Certain shift catalysts can contribute to high
methanol vapor emissions from hydrogen plants.
Ketone Dewaxing
Solvent losses from ketone dewaxing can be as much as half of a refinery's total toxic emissions. Sources of solvent
loss include ketone stripper tower bottoms to sewer, residual solvent in the products, fugitive leaks, solvent
contaminated drain system, and the blanket gas purge vent. Solvent lost in products is destroyed when the lubes
hydrotreater is downstream the ketone dewaxer, and in those cases, is not ultimately released to the environment.
Options to reduce emissions focus on improving the operation of the existing equipment as much as possible before
introducing new technology or making investment.
Ketone stripper tower bottoms losses to the sewer can be reduced by increasing tower bottoms temperature,
increasing tower feed temperature, equalizing feed rate by continuous feed of sump water, improving control logic to
better anticipate load swings, reducing sand fouling of tower internals, increasing the number of effective stages, and
installing an analyzer to measure solvent loss. Residual solvent in products can be reduced by installation of an
analyzer to monitor solvent loss, and debottlenecking product stripping towers. The above options have the potential
to reduce emissions by about 60 percent.
ExxonMobil proprietary Cat Dewaxing doesn’t use a solvent, but doesn’t produce a wax stream either, which can
have a significant environmental benefit and value.
MTBE
Much of the environmental impact of the MTBE synthesis process is due to the use of a large quantity of water which
is needed to remove catalyst threatening contaminants from the hydrocarbon feed stream. Spent water may contain
acetronitrile, ammonia, methanol, and other organics present in the feed. These can be minimized by reducing the
use of process water and/or finding a suitable disposition for the spent water other than wastewater treatment. Some
potential process changes include recycling spent water, using it in cooling services, as desalter wash water or as
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boiler feedwater. Recycling requires treatment such as steam stripping, ion exchange, or chlorination. Methanol is
used to make MTBE, and is infinitely water soluble and can represent a large BOD load to a WWTP. Therefore,
methanol emissions to refinery sewers must be controlled. MTBE plants should be provided with an isolated sewer
sump inside the MTBE unit, which is not released to the sewer until methanol levels are measured and low enough
not to present a problem.
Process Contact Steam Condensate
A significant source of wastewater (in terms of both flow and contaminant level) to a refinery treatment plant is
condensed steam. Non-contact condensed steam should be recovered in the plant, and ideally returned to the boiler
feedwater system. At a minimum, non-contact steam condensate should be recovered in the cooling tower return
water. Options for reducing steam consumption generally offer improved energy efficiency, lower water treating
costs, and environmental credits.
Steam usage can be reduced in vacuum pipestills by specifying mechanical vacuum pumps instead of steam jet
ejectors, use of recycled overhead gas as the stripping medium, and optimizing the coil/stripping steam ratio. In
sidestream strippers, specifying high efficiency (structured) packing instead of trays or random packing can reduce
steam use. Effective design of FCCUs should minimize steam needed to enhance catalyst circulation, to promote
catalyst/hydrocarbon contacting, and reactor stripping steam. Use of reboilers in sour water strippers instead of
direct steam injection significantly reduces the amount of stripped sour water generated.
Sewers
New designs should consider installing a 3 sewer system consisting of:
-
Clean water that does not require wastewater treatment (rainwater, demineralizer waste)
-
Contaminated rainwater that requires wastewater treatment (can be diverted to earthen basin or rainwater
storage tank)
-
Process contact sewer water that requires wastewater treatment, preferably in an aboveground system
Tankage
A large semi- continuous source of oil in refinery sewers is from tank water draws that go directly to sewer. Modern
designs should pipe all crude water draws to a dedicated crude water draw tank. The oil is then returned to crude
tanks, so no product downgrade is necessary.
Water draws from intermediates, products and imported gasoil tanks also need to be captured. Water draws from
these tanks should be piped to an offspec slop tank that is designed for oil/water separation. From there the oil can
be sent to a Coker, FCCU or Pipestill.
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Table 1: Approach To Manufacturing Plant Environmental Control
*See Note Below
ELIMINATION/MINIMIZATION
The reduction or elimination at the source, usually within a process.
Measures include process modifications, feedstock substitution,
improvements in feedstock quality, improvements in housekeeping and
management practices, and recycling within a process.
RECYCLE/REUSE
The use or reuse of a waste stream as an effective substitute for a
commercial product or as an ingredient or feedstock in an industrial
process. It can occur on or off site and includes the reclamation of
useful constituent fractions within a waste material, use of a waste
stream after removal of certain contaminants, water reuse, or the use
of a waste stream as a fuel supplement or fuel substitute.
TREATMENT
Any method, technique, or process that changes the physical,
chemical, or biological character of any waste stream in a way that
neutralizes the waste, recovers energy or material resources from
the waste, or renders such waste less hazardous, safer to manage,
amenable for recovery or reuse, amenable for storage, or reduced in
volume.
DISPOSAL
The discharging, depositing, injecting, dumping, spilling, leaking, or
placing of waste into or on any land or water so that such waste or
any constituents can enter the air or be discharged into any water,
including ground water.
* As a practical matter, there will always be some trace air and
wastewater emissions and disposal of wastes at an industrial facility.
Source reduction and recycling should be considered in projects only
to the extent that they are cost-effective or strategically justified, and
do not cause problems to other plant operations. For example, a
flare gas recovery compressor can significantly reduce flaring.
However, if excessive nitrogen is in the flare gas, the low BTU fuel
gas can cause firing problems (flame impingement, failure to meet
temperature targets, etc) at site heaters. Careful consideration must
be given to ensuring reliability of affected unit operations resulting
from source reduction/recycling efforts.
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Table 2: References To Major Environmental DP Sections
MEDIA
Air
POLLUTANT OR CONCERN
CONTROL TOPIC
SECTION
Hydrocarbons
Fugitives/Tanks/Waste Water/Loading
XVIII–A2
Toxics
Industrial Hygiene
Equipment/Practices
XVIII–B, B1
XVIII–A2
Particulates
Cyclones
Bag Filters
Scrubbers/Demisters
Electrostatic Precipitators
XVIII–A3
XVIII–A4
XVIII–A5
XVIII–A6
Combustion Products
(SOx, NOx, CO, Particulates)
XVIII–A, A5, A8
Dispersion
Impact Modeling
XVIII–A1
Noise
Flow Induced
Combustion
Machinery
Devices
Devices
Devices
XVIII–C, C1
XVIII–C, C2
XVIII–C
Water
NH3, H2S
Sour Water Strippers
XIX-A10
Oil
API Separators
Flotation Units
XIX–A1
XIX–A2
Suspended Solids
Media Filtration
Clarification/Thickeners/ Flocculation
Flotation Units
XIX–A3
XIX–A4, XX–A2
XIX–A2
Dissolved Organics/ Phenols/Oil and
related contaminant indicators, such as
BOD5, COD, TOC, Aquatic Toxicity
Biological Treatment
Activated Carbon Treaters
XIX–A5, A6, A7
XIX–A8
Chemical Oxidation
XIX-A11
Fresh Water Resources
Water Reuse
XIX-B
Sludge
Dewatering
Incineration
Stabilization
Biotreatment
XX–A1, A2, A3
XX–A5
XX–A6
XX–C1
Spent Caustic
Treatment/Disposal/Reuse
XX–C4
Groundwater
Containment
XX-B2
Remediation & Monitoring
XX-B3
Risk Assessment
XX-B1
Containment
XX-B2
Treatment
XX-B4, XX-C1
Risk Assessment
XX-B1
Free-Phase Product
Treatment, Recovery
XX-B6
Ponds & Lagoons
Treatment
XX-B5
Waste
Site
Remediation
Soil
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Table 3: List Of Major Emission Sources
SOURCE
CONTAMINANTS
COMMENTS
Alkylation
Acids, sludges, butadiene
Boiler Feedwater Production
Treating chemicals
Need to choose biocides, scale inhibitors and dosages carefully to
avoid impact on biotreatment, effluent nutrients and toxicity
Catalytic Reforming
Benzene, chlorine
Benzene leakage from valves.
Coking
CO, CO2, SOx, NOx, particulates,
metals, cyanide, sulfur, nitrogen and
phenolic compounds in wastewater
Sludge receptor.
Combustion
CO, SOx, NOx, CO2, toxics,
particulates
Large collective source of total plant primary air pollutants.
Emissions are taxed in some locations.
Cooling Tower
VOCs, several biocides, antiscaling
and dispersant chemicals used
Improved leak detection for VOCs. Choice of chemical additives to
control microbe biofouling growth and scale formation, particularly
when cycles are increased for water conservation
Desalting
Waste water, benzene, oil, sludge,
emulsions
Large volume (50–60%) of benzene contaminated oily water.
Large cost to control.
Flares
HCs, SO2, combustion products
Emissions may be reportable.
Fluid Cat Cracking
CO, CO2, SOx, NOx, particulates,
metals, cyanide, sulfur, nitrogen and
phenolic compounds in wastewater
Largest volume of primary air pollutants from single process
source. Regulatory pressure even for tightly controlled units.
Gas Treating
H2S, solvent leaks (organic nitrogen,
BOD5)
Gas Turbines
NOx
Hydrocarbon Steam Stripping
Sour water, benzene water
Hydrocracking
Spent catalysts, NH3, H2S
Hydrotreating
Spent catalysts, NH3, H2S
Isomerization
Spent catalysts
Ketone Dewaxing
Ketone leaks, waste water
Large source toxic emissions from single process unit.
Loading/Unloading
VOCs
Potentially large source of VOCs. Many locations require controls
Lubes Processing
Solvents (organic nitrogen, BOD5)
MTBE Plant
MTBE, methanol
Process Fugitives
VOCs, benzene
Large contributor of VOCs.
Product Treating
Spent caustic
Typical industrial disposal outlets disappearing. Upsets in WWTP.
Spent Catalyst
Metals
Traditional landfill not viable. Most metal bearing catalysts are
returned to vendor.
Sulfur Plant
SO2, H2S
Sulfur plant reliability a key issue.
Tankage
Water draws, VOCs, sludges
Large source of waste water, VOCs and sludge.
Wastewater Treating
VOCs, benzene, metals, inorganic
and biosludges, NH3, phenols,
COD/BOD, nitrate
Many source reduction opportunities. Sophisticated treatment
process units may be required. Biological systems are typically
the most cost-effective for organics, metal and toxicity removal.
Largest source of sour water.
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Table 4: Types Of Site Contamination
SOURCE
Accidental Spills
- Leaking tanks
- Tank Overfills
- Acid/Caustic Spills
- Piping Failures/flange leaks
- Fires
TYPICAL CONTAMINANTS
Crude
Products
Chemicals
Catalysts
Additives
Wastes
Disposal Practices
- Landfarms
- Landfills
-Tank Sludges
- Lagoons/Pits/Impoundments
- Dredged Spoils
- Oily Water Discharges
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Table 5: Components Of An Emission Reduction Program
EVALUATE THE WASTE STREAMS
Conduct emissions inventory
Prepare waste and wastewater flow and contaminant material balances (requires sampling and lab analysis)
Characterize waste (Toxicity, Quantity, Regulatory Impact)
Management costs
Safety and health risks
Potential for success
Potential environmental liability
IMPLEMENT LOW COST/OPERATIONS IMPROVEMENT ITEMS
Segregation of wastes (optimize treatment efficiency)
Improved material handling (to reduce material quantities)
Reuse/substitution/operational changes
Preventative maintenance
TECHNICAL EVALUATION
Product quality
Product safety
Worker health and safety
Maintenance requirements
Space requirements
Installation schedule
Production downtime
Reliability/Proven performance
Commercial availability
Permitting requirements/Community acceptance
Regulatory constraints
Effects on other environmental media
Personnel skills requirements
ECONOMIC EVALUATION
Capital requirements
Return on investment
Operating and maintenance costs
Life Cycle Cost Analysis
Consider Third Party Operation of Facilities (Most effective is solid waste sludge dewatering and disposal)
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Table 6: Emission Control Guidance
SOURCE
CONTROL OPTIONS
Alkylation
•
•
•
Catalytic
Reforming
•
•
•
Coking
•
•
Combustion
•
Ultra low NOx (ULNB) burners can achieve 25 ppm in boiler flue gas.
•
Addition of SCR (Selective Catalytic Reduction) can achieve 5 ppm NOx, but at 3 to 4 x
•
•
incremental cost.
Reduce emissions at individual sources.
Sub–micron particulate removal options
Desalting
§
§
§
§
§
Improved pumps and valves to reduce fugitive emissions
Flood systems/dikes to reduce impact of HF release.
Detectors to provide early warning of HF release.
• HF process/storage vents to water–spray scrubbers.
Ventless regeneration system.
Isolate wastewaters.
Use hot flue gas regeneration.
Enclosed structures for coke handling and storage.
Reduce sour water production by minimizing steam use.
• Improved COS removal from FLEXICOKING gas.
§
§
§
§
§
Use of EMRE mudwash design.
Use of the three AGAR probe design for desalter level control
Proper wash water selection and/or pH control facilities
Add demulsifier as far upstream as possible.
Keep water injection to the preheat train upstream of the desalter to no more than 1% on
crude.
Consider solids issues when designing the desalter brine handling system,
Use bielectric desalter design
For a new desalter, specify brine oil content to be less than 250 ppm.
All desalter instrumentation should be in the DCS system.
Consider water reuse options for desalter wash water.
Dewaxing
•
•
•
•
§
Condense blanket gas vapors.
Improve packing and maintenance.
Seal legs on drains.
Reduce hazard of emissions.
Temperature control of deketonizer.
Dimersol
•
Spent caustic contains Ni and Al. Do not reuse at WWTP.
FCC
•
•
ESP for particulate control.
Wet Gas Scrubber is most cost effective if particulates and SOx control needed.
•
•
•
DeSOx additives offer moderate control at low cost.
Other credits needed to make feed desulfurization attractive.
Thermal DeNOx for moderate control, SCR (Selective Catalytic Reduction) for greater
•
•
NOx control.
Control critical parameters that impact emissions.
CO boiler for CO control.
Flares
•
§
•
Recover vapor vents.
Reuse water as flare seal drum makeup
Flare gas recovery compressors
Hydrocracking/
Gofining
•
Water wash streams should use recycled water from another process
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Table 6 (Cont)
SOURCE
CONTROL OPTIONS
Intermittent
Releases
•
•
•
•
§
§
Use closed purge sampling systems where practical.
Coordinate sample volumes with test requirements.
Restock unused paint.
Drain process vessels to closed system or fract tanks for separation before going to
sewer.
Offsite disposal of MEA reclaimer sludge
Include clearing headers in design of process units to route flush material to a closed
system to keep out of sewer.
Loading
•
•
•
•
•
•
•
Absorption
Adsorption
Vapor balancing.
Thermal oxidation.
Catalytic oxidation.
Carbon adsorption.
Refrigeration
MTBE
•
Replace wash water recycle loop with individual loops for methanol extraction/recovery
and feed washing.
May not be easily stripped or removed by conventional treatments
Use of a feed treater instead of a feed wash tower.
Alternates to wastewater treatment for feed wash water.
§
•
•
Process Contact
•
Steam Condensate •
•
•
Dry vacuum distillation.
VPS vacuum pumps vs. steam jet ejectors.
Recycle VPS overhead gas as stripping medium.
Replace sidestream stripper trays with packing.
Process Fugitives
•
•
•
•
75–90 percent reduction of uncontrolled emissions achievable via practice changes annual inspections, graphite packing replacement.
Enhanced (“smart") inspections, which target the few significant sources, are cost–
effective step.
Use 5–ring valve packing with three low density graphite sealing rings and braided or
composite rings.
Use ESVP (Extended Stem Valve Packing) for Reformer MOVs (Motor Operated Valves).
Use rupture disks with pressure relief valves.
Consider sealless (mag drive, canned) pumps as replacements, or install double seals.
Consider environmental impact in equipment selection.
Product Treating
(Spent Caustic)
•
•
•
•
Cascaded reuse in less severe service.
Wash or condense Merox vents to remove sulfur compounds.
Replace caustic treating with regenerable treating (e.g. Merox, amine).
Regenerate spent caustic.
SOx Management
(overall)
•
Optimum priority for control is: (1) sulfur plant, (2) combustion controls, and (3) FCC
controls.
Spent Catalyst
•
•
•
•
•
•
•
•
Cascaded reuse in less severe service.
Use as filler in construction materials (e.g. cement, asphalt, and brick).
Offsite total recovery systems (e.g. CRI–MET).
Onsite integrated treatment and recycle (e.g. MAGNACAT, DEMET).
Upgrade feed quality.
Minimize inventory.
Reuse spent phosphoric acid polymerization catalyst as biox nutrient.
Increase catalyst life.
•
•
•
ExxonMobil Research and Engineering Company – Fairfax, VA
ExxonMobil Proprietary
Section
XVII
Page
20 of 20
PLANT ENVIRONMENTAL CONSIDERATIONS
DESIGN PRACTICES
February, 2004
Table 6 (Cont)
SOURCE
CONTROL OPTIONS
Sulfur Recovery
•
Tankage
•
•
•
•
•
•
•
§
Double rim seals on external floating roof tanks.
Liquid mounted in place of vapor mounted seals.
Slotted guide pole sleeves
Internal floating roofs on fixed roof tanks.
Tankage minimization.
Tankage vapor recovery systems.
Route tank water draws to separate oil/water separation equipment.
Mixers on crude tanks to minimize sludge deposition
WWTP
•
•
Major troublesome sources of oily water are desalter and tank water draws.
Steam stripping is major source of sour water., but stripping essential to remove sour H2S
and NH3 to acceptable levels prior to further treatment
Inadequate housekeeping, practices still a major contributor.
Water flow (versus oil content) is key parameter for facility sizing and impact
Reduction in soluble , non-biodegradable organics, where possible to reduce BOD /COD
load. Use light napthas vs. aromatic oils for diluents
Trend towards closed, above ground treatment facilities (including sewers).
Segregate streams for upstream treatment.
Reuse water within process or in another process.; example reuse stripped sour waters
(SWS bottoms) for desalter feed makeup (reduces phenols)
Reduce sludge volume via sewer segregation, wastewater reduction, feed to cokers.
•
•
§
•
•
•
•
Consider adding a third stage Claus catalytic reactor.
• Catalyst selection for destruction of other sulfur species
§ Add tail gas clean-up unit (TGCU).
ExxonMobil Research and Engineering Company – Fairfax, VA