Richard A. Corbett
Refining/Petrochemical Editor
Refineries and petrochemical plants face tough regulations on emissions of hazardous wastes and air emissions during the next decade.
During the 1990s, process plants will have to substantially change the way they generate, handle, store, and dispose of hazardous wastes, particularly spent catalysts, and they will likely have to substantially reduce air emissions.
The disposal and treatment of hazardous wastes is governed by the Resource Conservation and Recovery Act (RCRA) of 1976, and the Hazardous and Solids Waste Amendments (HSWA) of 1984.
Reauthorization of the Clean Air Act of 1970 will likely tighten rules on emissions from plants, and for refiners, rules on how their products are formulated to reduce emissions when the products are consumed.
RCRA and the HSWA amendments set strict requirements on how hazardous wastes may be handled, how they may be remediated, and how they may be disposed of safely. In general, the regulations are meant to discourage land disposal of hazardous wastes without treatment. By the early 1990s, sending hazardous wastes to landfills and disposal wells will be prohibited, for the most part.
With respect to air emissions, refiners are making good use of technology to reduce them. In particular, catalytic reduction of nitrogen oxides (NOx) emissions has proven successful.
An example of the efforts process plant operators are making to reduce or remediate hazardous waste is a water treatment process at Hoechst-Celanese Chemical Group Inc.'s Pampa, Tex., acetic acid plant. The water treatment is being used to make plant wastewater containing organic compounds suitable for use as irrigation water for growing hay on a company-owned farm near the plant.
Other examples include the use of approved incinerators by Phillips Petroleum Co. and Hoechst-Celanese to reduce substantially both liquid and solid wastes.
An important area of concern for process plant operators is the disposal or recycle of spent process catalysts. Particular attention is directed toward the disposal or recycling of spent FCC equilibrium catalysts and spent hydrotreating catalysts. These catalysts, for the most part, are not yet considered hazardous by EPA, but the industry is concerned that they soon may be.
A spent hydrotreating catalyst reclamation plant, described in detail, is typical of facilities refiners will rely more on for the disposition of spent catalysts.
RCRA AND HSWA
The RCRA and the HSWA amendments prohibit process plant operators from disposing of hazardous wastes, unless those wastes have been remediated to nonhazardous wastes. The statutes also regulate the way the wastes are to be treated, stored, and disposed of, and require that all listed wastes be tracked by manifest from their generation to their final disposition (cradle to grave).
RCRA is aimed primarily at preventing waste disposal problems that lead to the need for programs such as the Comprehensive Environmental Response, Compensation, and Liability Act (Cercla), better known as the Superfund program. For that reason, releases of hazardous wastes before Nov. 19, 1980, were expected to be cleaned up by the Superfund program, and releases after that date by RCRA.
HSWA was enacted to spur EPA and regulatory authorities to improve the hazardous waste management provisions of RCRA. One major goal of HSWA is the presumptive prohibition of land disposal of all hazardous wastes, set by statutory minimum controls.1
If the EPA does not selectively override the disposal ban for a listed waste by the statutory deadline, a self-implementing total ban goes into effect. The self-implementing bans are referred to as HSWA's "hammer" provisions.
The regulations can be considered all-encompassing because various sections apply to facilities that generate, treat, transport, dispose of, and store hazardous wastes. Process plants, in the normal course of business, do all of those things and are subject to all of the provisions of the regulations, including provisions requiring a permit to operate hazardous waste-treatment facilities on their premises.
EPA is charged with classifying hazardous wastes. Waste materials are considered hazardous if, by a specified test, they are determined to be toxic, reactive, ignitable, or corrosive.
EPA currently lists five specific hazardous wastes generated in refineries: Dissolved air flotation (DAF) float, slop-oil emulsion solids, API separator sludge, heat exchanger bundle cleaning sludge, and tank bottoms that contain lead compounds. These are identified by EPA as K048 through K052 on its K list of hazardous wastes from specific sources.
There are also other lists of hazardous wastes: The F list for wastes from nonspecific sources, the U list for toxic wastes, and the P list for acutely toxic wastes. In addition to these specified wastes, EPA has the authority to add other materials to the list by the use of specific test procedures. Spent catalysts are likely to be included on an expanded list of hazardous wastes.
Rules also apply to mixtures of hazardous and solid wastes. These are called the derived-from rules, and the mixtures, therefore, are considered hazardous.
All of these wastes, due to HSWA hammers, are subject to prohibition from land disposal.
In order to dispose of hazardous waste materials, the wastes must be treated to render them nonhazardous. Treatment standards will be specified as the best demonstrated available technology (BDAT).
After August 1990, any wastes that can be treated by BDAT systems will be banned from land disposal unless EPA grants an exemption on a case-by-case basis. A possible exemption may be available if a processor can verify that a land fill or land farm on company property can ensure no migration of materials from the facility (water runoff, leaching into ground water, etc.).
SOME PLANT SOLUTIONS
Refiners are taking steps to remediate oily sludges and the materials on the EPA F list in order to comply with the land ban restrictions.2
One company will partially dewater the hazardous solids, blend them with recovered slop oil, and process the blend in fluid cokers. The RCRA regulations allow this processing option.
Another company will look at ways to meet BDAT standards to allow land disposal after August 1990. Some of the options are filter pressing, followed by solvent washing and thermal desorption of oily sludges, including DAF float and AP[ separator sludge.
Oily waste sludge, after heat, chemical, and settling treatment, can also be centrifuged to further separate the oil, water, and solids. The solids from the centrifuge are combined with API separator bottom sludge, and filter pressed.
The dry filter cake, along with heat exchange bundle cleaning sludge, is drummed and sent to a hazardous waste disposal site, a land farm, or after 1990, to a licensed incinerator.
INCINERATORS
Because processing plants may not be able to meet BDAT standards on-site, and particularly if they do not have disposal facilities such as land farms, incineration will be one of the prevalent ways to dispose of these wastes.
EPA has approved liquid and solid waste incinerators as BDAT systems if the incinerator destroys 99.99% of the hazardous materials sent to the incinerator. This performance level has been called the "four-nines" performance standard.
An example of an incinerator that meets the BDAT standard is a demonstration unit installed at Phillips Petroleum Co.'s research center in Bartlesville, Okla., that can incinerate about 1 million lb of solid and liquid waste per year (Fig. 1). The unit, started in June 1984, became the first hazardous waste incinerator to receive an operating permit under RCRA.
Incineration takes place in a rotary kiln at 1,200-1,700 F.
Additional incineration takes place at 1,900-2,400 F. in an afterburning section. The success of the incinerator at Bartlesville led to the design and pending construction of a larger-scale unit at Phillips 66 Co.'s refining and petrochemical complex in Sweeny, Tex. The capacity of the unit will be about 30 million lb of waste per year, and it will operate in excess of the 99.99% BDAT standard. According to Phillips, the unit will destroy 99.9999% of the chemical liquid and solid wastes sent to the incinerator.
Phillips expects to begin construction of the incinerator sometime during 1990, pending a permit from the Texas Air Control Board (TACB), and the Texas Water Commission. Texas regulations require concurrent approval from both agencies before construction of the incinerator can begin.
After the permit is obtained, public notice must be given of the intent to construct an incinerator on the site, and public comment solicited, through a public forum. Once that is completed, a construction permit can be issued.
Phillips expects no problems with obtaining the necessary permits to allow construction to begin in 1990. Start-up is slated for about 1 year from receipt of the construction permit.
Another example of incinerator use is at Hoechst-Celanese Chemical Group Inc.'s Bishop, Tex., chemical plant. Two ceramic-lined incinerators are installed at the plant to reduce organic emissions into the air.
The incinerators are fed organically laden vent gases from three units that oxidize methanol to make formaldehyde. The vent gases are incinerated at temperatures up to 1,800 F.
The incinerators destroy the hazardous materials in the incoming vent gases. Heat generated in the incinerators is used to make steam in waste-heat recovery steam generators installed on the incinerators.
NOVEL WASTE REDUCTION METHOD
The Pampa, Tex., plant of Hoechst-Celanese Chemical Group has installed a treatment facility to biochemically degrade organic material in the plant's wastewater streams.
According to Bob Maurer, manager, environment quality for Hoechst-Celanese Chemical Group, Dallas, the plant's wastewater is treated and then used for irrigation of a 300-acre, company-owned land farm that produces alfalfa and grasses that are sold to cattlemen in the area (see cover). The treatment system completed its first full growing season in 1989.
The treatment system is designed to handle about 1 million gpd of wastewater containing 0.5-1.0% organic material, including acetic acid, the primary product made at the plant. The wastewater is treated on site in a four-step process and sent by pipeline a short distance to the farm.
All of the plant's wastewater streams are collected and equalized in feed equalization tanks. The water then enters an anaerobic reactor where approximately 20% of the organic materials are digested.
From there, the water undergoes aerobic treatment in an activated-sludge system.
The nonhazardous sludge is blown down from the system and sent to the land farm as is the treated water.
The wastewater is then suitable for irrigation of crops grown on the farm. Any traces of organics that remain in the wastewater and sludge are biodegraded at the surface of the soil. The wastewater also contains nitrogen and phosphates which provide added nutrients to the crops.
The entire system contains the wastewater on company property, and the land farm is designed so that no run off of treated water occurs. This tight control over the plant's wastewater, from process to land farm, is in accordance with a no-discharge permit from the Texas Water Commission.
NOX REDUCTION
Reauthorization of the Clean Air Act of 1970 will likely result in rules to further reduce process plant emissions into the air. Some innovative technology is available to reduce nitrogen oxides (NOx) emissions, one of the difficult emissions to control .2 Two technologies available to reduce NOx emissions are: Selective Non-Catalytic Reduction, and Selective Catalytic Reduction (SCR) licensed by Foster Wheeler Energy Applications Inc., Livingston, N.J. (Fig. 2).3 Noncatalytic reduction requires the injection of a reducing agent, such as ammonia or urea. SCR operates with ammonia injection only. Both processes convert NOx to nitrogen and water vapor.
Noncatalytic reduction is particularly applicable to CO boiler vent streams where flue-gas streams are at 1,600-1,800 F., an optimum condition for the noncatalytic reactions. The process can remove 50-70% of the NOx from the flue gas.
Selective Catalytic Reduction can operate at lower flue-gas temperature, in the range 500-770 F. The process can remove up to 90% of NOx in gas and oil-generated flue gas streams.
The quantity of ammonia added to the flue gas is about 1 mole ratio of NH3/NOx, and most of the excess ammonia is decomposed to nitrogen and steam by catalytic action.
The catalytic section of the SCR process utilizes a honeycomb catalyst system, housed in bucket-type cartridges so that the operator does not handle raw catalyst.
SPENT CATALYST HANDLING
Process plant operators are becoming increasingly concerned with how to handle spent process catalysts, particularly FCC equilibrium catalysts and hydrotreating catalysts. These two catalysts are not yet listed as hazardous wastes, but EPA is eyeing these for hazardous determination tests.
These catalysts contain contaminants that were picked up in the processes in which they were used. And there is still limited specific technology to remediate the contaminants to allow disposal as nonhazardous waste in land fills.
Spent FCC catalyst can at present be disposed of in sanitary landfills or sold to other refineries.2 Other methods include chemical fixation and sale to Portland cement manufacturers. Dry disposal and disposal in land farms is not acceptable.
Several refiners have found that selling spent FCC catalyst to cement kilns is attractive because the cement kilns need a source of alumina, and the catalyst is chemically consumed in the cement-making process.
Unfortunately, many refiners are concerned about the liability involved in the future. And cement manufacturers will only take the catalyst as long at it is considered nonhazardous.
If EPA or local regulations were to list the catalyst as hazardous waste, it is doubtful cement manufacturers would want to go through the difficult process of meeting RCRA regulations governing waste-handling operations.
For nickel molybdenum and cobalt molybdenum hydroprocessing catalysts, the handling route most favored is recycling .2 Even though these catalysts are currently considered nonhazardous, refiners are concerned with the long-term (actually perpetual) liability connected with disposal in secure disposal facilities.
Spent hydroprocessing catalysts are not considered acceptable for disposal in sanitary landfills or land farms. They can be disposed of if they are chemically fixated and stored in a secure landfill.
If the catalysts can be successfully regenerated, they can be reused to reduce the need for disposal. There is also the possibility of complete reclamation of the components of the catalysts, where each of the components would then be considered nonhazardous materials that could be sold as raw materials.
There are several metals reclamation companies operating in the U.S., Canada, and Europe that can reclaim the metals from hydroprocessing catalysts and recycle the materials.
In an effort to develop new technology to address environmental challenges facing the oil industry, an industry research group was formed in early 1989. The group, the Petroleum Environmental Research Forum (PERF), was formed under the provisions of the Cooperative Research Act to specifically address environmental problems facing the petroleum industry.
PERF invites industry and outside participation in R&D projects directed at meeting the industry's environmental challenges. Each participant shares in the project expenses and data. Results and technologies gained from the research are the exclusive property of the participants.
PERF is currently working on a project to develop information and technology for handling, recycling, and remediating spent refining catalysts. The project has just recently started.
CATALYST RECYCLING
Spent catalyst recycling is gaining popularity with refiners as the RCRA land bans go into effect. Several companies in the U.S. are installing facilities to reclaim spent catalysts.
With recycling, the metals on the spent catalyst are reclaimed for sale to the general metals market, and the remaining materials are either sold or disposed of under RCRA rules.
A typical example of a facility to reclaim spent hydroprocessing catalyst is the Port Nickel plant of AMAX Metals Recovery Inc. located in Braithwaite, La. The plant uses the licensed process technology of CRI-MET, Houston. CRI-MET is a partnership of AMAX Inc. and Shell Oil Co.
The CRI-MET process converts spent catalysts into four products:
- Molybdenum trisulfide, MoS3
- Vanadium pentoxide, V2O5
- Alumina trihydrate, Al2O3-3 H2O
- Nickel cobalt concentrate.
Other than the four products, treated wastewater is the only stream that leaves the recovery plant. All materials arriving at the plant are stored in approved storage facilities.
In the process (Fig. 3), spent catalyst is fed first to a grizzly screen to remove foreign material and trash, and then to a hopper. Both are connected to a wet scrubber for dust control. The catalyst is then conveyed to an agitated slurry tank.
The screened catalyst, slurried in a dilute recycle caustic-alimunate solution, is pumped to a ball mill where it is ground and then stored in two large, agitated tanks.
The catalyst slurry is next subjected to a high-temperature oxidizing leach to convert the sulfide sulfur to sodium sulfate and to dissolve vanadium and molybdenum as sodium vanadate and sodium molybdenate. A high-solids slurry from the ball mill is diluted appropriately with a recycle caustic-sodium aluminate solution for leaching in a spherical autoclave.
The autoclave has dual feed systems, each with a pump and heat exchanger. One system feeds a slurry, and the other feeds the dilute recycle leach solution. Compressed air is injected as a source of oxygen.
The leach reaction is maintained at a basic pH. The autoclave vent gas, mostly nitrogen, passes through a water-cooled pressure condenser where any nonoxidized organic vapors are condensed for recovery or recycle. The slurry is discharged into an atmospheric tank and neutralized to remove aluminum and phosphorus from the leach solution.
The neutralized leach slurry is fed to a conventional thickener where the solids are concentrated. The thickener underflow is fed to a vacuum drum filter to separate solids.
The filtrate is returned to the thickener, combined with the thickener overflow, and pumped through precoated polishing filters for clarification.
The neutral sodium molybdenate and vanadate solution is acidified with sulfuric acid and then treated with hydrogen sulfide. Molybdenum is precipitated as molybdenum trisulfide, and the vanadium is reduced to vanadyl sulfate. Any excess hydrogen sulfide is vented from the reaction tanks into a packed column, where it is scrubbed with a strong caustic solution.
The slurry of molybdenum trisulfide is filtered, and the solids are washed with water and filtered again. The molybdenum product is dried and then packaged in bags for shipment to a molybdenum conversion plant where it is roasted to the final product, molybdenum trioxide.
The wash solution is returned to the front end of the plant. The filtrate, after moly precipitation, is clarified by a polish filtration and neutralized continuously in two agitated tanks in series by adding sodium hydroxide. Neutralization causes vanadium to precipitate completely as vanadium hydroxide.
Liquid/solids separation and washing of the vanadium hydroxide precipitate is achieved with the use of high-efficiency, counter-current decantation in thickeners. This system provides efficient washing that assures low sodium content in the product.
The process solution from the vanadium thickeners is directed to a large settling tank for further clarification and then sent to the wastewater treatment system. Any solids collected in this tank are recycled to the vanadium precipitation tanks.
The washed vanadium hydroxide solids are dewatered in a centrifuge and pumped to a calciner. The solids are dried and heated in an air atmosphere at about 1,100 F. to form semisintered vanadium pentoxide granules. This final product is packaged in bags and shipped to ferro-vanadium producers.
The solids from the first-stage leach are slurried with strong caustic recycle liquor and fresh caustic and fed to a second-stage leach. Alumina and residual molybdenum and vanadium are dissolved in this leach stage.
The autoclave has two feed systems, one for a heavy slurry and another for the strong recycle solution. Each incorporates a positive displacement pump and heat exchanger. The solids concentration is controlled at a level that maximizes metal extraction, but avoids instability of the leach solution.
The autoclave slurry discharges into an atmospheric flash tank and is then fed to a two-stage centrifuge system for liquid/solids separation and washing. The centrate from the second centrifuge stage is a dilute caustic soda-sodium aluminate solution which constitutes the weak recycle solution that supplies caustic for feed preparation and the first-stage leach.
The solids from the centrifuge's second stage are fed to a dryer. The final nickel-cobalt concentrate product is calcined and shipped to various customers.
The strong caustic soda-sodium aluminate solution from the first centrifuge stage is pumped to a thickener for clarification. Solids are returned to the second-stage leach.
The overflow solution is polish filtered. A heat exchanger is in the circuit to prevent alumina precipitation from this highly concentrated leach solution.
The thickener overflow, after being further polished, is mixed in an agitated tank containing alumina trihydrate, and pumped through a watercooled heat exchanger to decrease the temperature. From there, the slurry goes to a large, circulated precipitation tank that contains aluminum trihydrate solids.
Contacting the alumina-rich solution with the solids results in precipitation of aluminum trihydrate from the leach solution. The precipitation tank is circulated with a centrifugal pump.
A slurry stream is withdrawn from the bottom of the tank and pumped to a centrifuge. The centrate is recycled to the second stage leach. Solids from the centrifuge are repulped twice in water and centrifuged.
All three centrifuges operate continuously. Wet aluminum trihydrate from the third centrifuge is fed to a dryer, and the final product is shipped in bulk to local customers.
Wash water from the vanadium hydroxide thickeners and rainwater collected within the plant boundaries are combined and processed through a wastewater treatment plant. Sodium hydroxide is added to the wastewater to precipitate trace amounts of metals, if present.
Precipitated solids are removed in a thickener, and recycled to the process. The thickener overflow goes to a tank where pH is adjusted to required limits by addition of sulfuric acid. The wastewater is then filtered, pumped to a holding tank, and discharged under permit.
REFERENCES
- Fenster, David E., "Hazardous Waste Taxes and Regulations: Impact on the U.S. Petroleum Refining Industry," The University of Texas, Austin, 1988.
- National Petroleum Refiners Association Question and Answer Session on Refining and Petrochemical Technology, transcript, New Orleans, Oct. 4-6, 1989.
- Cvicker, John S., "Flue Gas Denitrification Using the Selective Catalytic Reduction Process," Foster Wheeler Energy Applications Inc., Livingston, N.J.
- LaRue, T., Tinnin, Ray, Wiewiorowsi, W., and Crnojevich, R., "AMAX Port Nickel, A New Dimension in Reclaiming Spent Catalysts," AMAX Metals Recovery Inc., Braithwaite, La., January 1988.
Copyright 1990 Oil & Gas Journal. All Rights Reserved.