Glenn E. Emery
Williams Pipe Line Co.
Kansas City, Kan.
Williams Pipe Line Co. (WPL), Tulsa, modified its tank-bottoms reclamation operation at Kansas City, Kan., to meet strict benzene-content levels established by the U.S. Environmental Protection Agency (EPA).
Since 1985, WPL has operated a plate-and-frame filter press (OGJ, June 30, 1986, p. 75) to reclaim all tank-bottom material generated throughout the WPL system. The filter press has helped eliminate long-term liability associated with hazardous-waste generation and disposal.
In September 1990, the EPA published its toxicity characteristics (TC) rule that established a new toxicity limit of 0.5 ppm for benzene contamination in solid wastes. Waste with more than this limit was to be classified as hazardous.
WPL's subsequent tests of filter cake from its press showed that a substantial portion contained levels of benzene that exceeded the new regulatory limit.
To maintain the filter press' status as a reclamation facility, WPL recognized that it would have to reclaim benzene from the filter cake.
In 1991, WPL built a filter-cake dryer and vapor-recovery system downstream of the filter press to reclaim the benzene and other hydrocarbons remaining in the filter cake.
WILLIAMS' SYSTEM
WPL owns and operates an 8,500-mile petroleum products pipeline system throughout a 10-state area in the Midwestern U.S. Products transported include gasolines, fuel oils, and aviation fuels, as well as LPG and crude oil.
The products are distributed to customers through 37 company-owned truck-loading terminals and several pipeline connections to other pipelines and terminals.
Currently, WPL has approximately 630 active storage tanks throughout its System that have a combined capacity of nearly 30 millon bbl. Each tank is cleaned and inspected routinely, resulting in approximately 15,000 bbl/year of tank-bottom material.
Fig. 1 indicates the typical composition of tank-bottom material.
In compliance with the federal government's Resource Conservation and Recovery Act (RCRA) of 1976, EPA published regulations in 1980 which addressed the handling and disposal of tank-bottom material.
As a result, the costs and liability associated with the disposal of tank-bottom material increased substantially.
Review of available technologies and how they fit with the regulations resulted in the decision to purchase and operate a filter press to reclaim all of the tank-bottom material generated in the WPL system. This option allowed WPL to reduce waste, optimize material handling, and reduce liabilities and costs.
REGULATIONS
RCRA was passed by the U.S. Congress in 1976 to amend the Solid Waste Disposal Act of 1965 and establish a comprehensive solid-waste regulatory system. The primary objective of RCRA was to establish a statutory framework for a national system to ensure the proper management of hazardous wastes.
RCRA's Subtitle C contains this framework and mandates a cradle-to-grave system of managing hazardous waste. Section 3001 of Subtitle C requires the EPA to write and publicize regulations that identify the characteristics of hazardous waste and to list wastes which should be managed as hazardous under the regulatory system.
Final regulations were published in 1980 and are found in Title 40 of the Code of Federal Regulations (CFR), Parts 260-268, 270, 271, 272, 280, and 281 (hazardous wastes regulations), and Parts 116 and 117 (hazardous substance discharge regulations).
CFR 261 carries out the intent of Section 3001 and is divided into four parts:
- Subpart A lists the purpose and scope of Part 261 and provides the basic definitions for a solid waste and a hazardous waste.
Also included are a list of materials not considered solid wastes for the purposes of Part 261 and special requirements for hazardous waste generated by conditionally exempt small-quantity generators and for hazardous waste which is used, reused, recycled, or reclaimed.
- Subpart B provides the criteria for identifying the characteristics of hazardous waste and for listing specific hazardous wastes.
- Subpart C lists four characteristics of hazardous wastes: ignitability, corrosivity, reactivity, and toxicity. These characteristics are used by persons handling solid wastes to determine if a waste is hazardous.
- Subpart D lists specific hazardous wastes and assigns a unique EPA hazardous-waste number to each.
In 1986, the EPA began to revise the existing toxicity characteristic identified in Subpart A to broaden the scope of the RCRA hazardous-waste regulatory program and to fulfill specific statutory mandates under the Hazardous and Solid Waste Amendment of 1984. The proposed rule was called the toxicity characteristic (TC) rule.
The final TC rule, published in September 1990, added 25 organic chemicals (italicized in Table 1) to the TC list and changed the testing method from the old extraction procedure (EP) leach test to an easier, more reproducible TC leaching procedure. In developing the TC rule, the EPA used a new mathematical computer model to simulate what happens to hazardous waste in a landfill.
All regulatory levels for hazardous chemicals derive from health-based concentration thresholds and a dilution-attenuation factor specific to each chemical.
The concentration threshold indicates the exposure quantity of a chemical before human health is affected; the dilution-attenuation factor indicates how easily the chemical could leach into groundwater.
The TC rule set the new limits on the 25 substances by multiplying the associated health-based number by a dilution-attenuation factor of 100.
Limits established for substances under the EP toxicity characteristic remain the same but require application of the new test.
SOLID WASTE
A solid waste is defined in 40 CFR 261 as any discarded material not specifically excluded from this classification. A discarded material is any material which is:
- Abandoned-by being disposed of, burned or incinerated; accumulated, stored or treated before being disposed of,
- Recycled-used in a manner constituting disposal; burned for energy recovery, reclaimed, accumulated speculatively; and,
- Inherently waste-like. This definition covers solid materials as well as liquid materials, contained-gaseous materials, or any combination of the three.
A hazardous waste is defined in 40 CFR 261 as a solid waste which is not specifically excluded from regulation as a hazardous waste and meets any of the following criteria:
- Exhibits characteristics of a hazardous waste as identified in Subpart C; or,
- Is listed in Subpart D; or,
- Is a mixture of a solid waste and one or more hazardous wastes listed in Subpart D.
TANK-BOTTOM MATERIAL
The cleaning process removes various quantities of water, product, and solids (sand, dirt, solidified fuel, scale, and rust) from the bottoms of refined petroleum storage tanks.
The classification of tank-bottom material according to EPA regulations depends upon how it is handled.
In accordance with 40 CFR 261.33, tank-bottom material is a Mixture Containing a commercial chemical product. If a commercial chemical product is discarded in a manner constituting disposal, 40 CFR 261 establishes the material as a solid waste. Subparts C and D of 261 identify the criteria for determining if a solid waste is hazardous.
Subpart C defines a solid waste as hazardous if it exhibits one or more of four specified characteristics-reactivity, corrosivity, ignitability, or toxicity.
Extensive testing determined that gasoline tank-bottom material generally has a flash point of less than 140 F. and is, therefore, ignitable. It also contains levels of benzene which exceed toxicity limitations established with the TCLP rule.
However, not all tank-bottom materials exhibit hazardous characteristics. (Even the premium leaded gasoline tank bottoms tested did not exceed the toxicity limitations for lead.)
Subpart D names specifically listed hazardous wastes. The only listed waste which could apply to tank bottom material is EPA Hazardous Waste No. K052, "Tank Bottoms (Leaded) from the Petroleum Refining Industry."
WPL has determined, through correspondence with the EPA, that this waste number applies only to tankage at refinery sites, not to pipeline or terminal tankage. Therefore, pipeline or terminal tank-bottom material is not considered hazardous under Subpart D.
Under 40 CFR 261.2 (c), a commercial chemical product which is reclaimed and which exhibits only a characteristic of hazardous waste is specifically excluded from definition as a solid waste. In 261.1 (c), a material is reclaimed if it is processed to recover a usable product.
Therefore, if tank-bottom material is handled in a manner constituting reclamation rather than disposal, it would no longer be classified as a solid waste and thus not be subject to designation as a hazardous waste. Transportation, storage, and reclamation would, therefore, not be regulated under 40 CFR 261.
(It should be noted that specific state regulations should be reviewed because they may differ from U. S. EPA regulations and in some cases be more stringent.)
RECLAMATION CENTER
In response to RCRA, EPA published in the early 1980s regulations which had a major impact on the pipeline and terminal companies involved with tank-bottom material handling.
WPL investigated various handling methods. Options for handling the tank-bottom material Were discussed with the EPA regions and various state environmental agencies to determine each option's classification under the agencies' various regulations.
The study indicated that reclamation of tank-bottom material was environmentally and economically the best solution.
WPL purchased a trailer with a filter press and associated equipment and began operations in September 1985 at a company-owned terminal facility in Kansas City, Kan.
WPL conceived the operation as mobile between locations of tanks being cleaned. After operations began, however, the company determined that a centrally located operation was more efficient because of the number of locations and tanks involved.
It was much easier to maintain one set of local operating permits and transport the tank-bottom material to the filter press.
In operations since that time, WPL has modified the filter press, added additional equipment to maintain status as reclamation, and made other location enhancements to improve operations.
Fig. 2 shows a process diagram of the current reclamation operation.
MATERIAL RECEIPT
Tank-bottom material is only transported to the reclamation facility aboard un-baffled, single-compartment trucks. Deliveries are restricted to only that material which can be pumped into a transport.
Experience has shown that material with a solids content of 20% or less will meet this criterion.
The concrete transport unloading area is designed for spill containment. Depending upon the material to be received, an inclined portion of the unloading area may be used to help induce the material to flow to the pump.
An air-driven diaphragm pump moves the material from the transport through a manifold to one of three holding tanks. The manifold is designed to allow material receipts into one holding tank, while another holding tank supplies the filter-press operation.
Each holding tank has a self-actuating mixer to ensure that the heavier solids do not settle to the bottom of the tank before being introduced into the filter press.
After unloading, all transports receive a high-pressure water rinse that effectively removes any remaining residue or solids which have settled during transport.
FILTER-PRESS OPERATIONS
The filter press consists of a series of recessed filter plates mounted vertically on two slide support bars (Fig. 3). The support bars are connected at one end to a fixed head and at the other end to a closing head.
An hydraulic closure unit attached to the closing head compresses the filter plates, creating a series of recessed chambers. These chambers become the actual filtering unit. Filter cloth on both sides covers each filter plate.
To initiate a process cycle, an operator activates the hydraulic closure, creating the filtering chambers. Water circulates through the filter press to purge each chamber of air.
After the air has been evacuated, a mixture of diatomaceous earth and water is introduced into the filter press. A common filter aid, diatomaceous earth collects on each of the filter cloths, forming a thin precoat layer. This layer serves as a filter and also protects the filter cloths from the tank-bottom material which is about to be introduced.
After the precoat layer has been established on the filter cloths, the press is ready to receive the tank-bottom material.
Achieving the desired liquid-solid separation during processing requires conditioning of the tank-bottom material with lime and diatomaceous earth as the material is being introduced into the filter press.
This conditioning helps coagulate the fine solid particles contained in the tank-bottom material, allowing more solids to be removed during processing. It also prevents the filter path from being clogged prematurely. A diagram of the actual flow through the filter press is shown in Fig. 4.
The conditioned feed is pumped through a center hole in the end plate and into the recessed chambers created between the filter plates. A center hole in each plate allows the feed to pass through the filter press and thus fill each chamber.
The solid portion of the feed collects on the outside of each filter plate, while the liquid portion is filtered through the precoat layer and the filter cloth.
This liquid portion or "filtrate" is collected through drain ports located on the corners of each filter plate and directed to a single discharge line on one end of the filter-press unit.
The cycle is completed when all of the filter chambers have become packed with solid material. This is indicated by the inability of the feed pump to introduce any more tank-bottom material into the unit.
Approximately 80 psi is achieved on the feed inlet at the end of a cycle. This pressure is maintained for at least 15 min to help dry the accumulated solid material or "filter cake."
At the completion of the cycle, the hydraulic unit on the closure head is retracted and each filter plate is manually separated, allowing the filter cake to fall from the recessed chambers.
Some manual scraping of each filter plate is also necessary to remove all of the solid material fully. Once all of the filter cake has been removed, another cycle can be initiated.
The petroleum product in the tank-bottom material tends to cause the filter cloths to clog or "blind off" which reduces liquid flow through the cloths. Periodic cleaning of the filter cloths with a high-pressure steam cleaner prevents this dogging.
Routine inspection of the filter cloths also ensures that no rips or tears in the cloths exist. The filter cloths can last for approximately 100 runs of the filter press before needing to be replaced.
The filter press operated by WPL is equipped with 43 plates, each approximately 4 x 4 ft in size. How much tank-bottom material can be processed per cycle largely depends on the solids content of the material.
Typical cycle sizes for this unit will range from 50 to 150 bbl. Each cycle requires approximately 4 hr to complete and will generate approximately 2 cu yd of filter cake.
UPGRADED SYSTEM
The dryer and vapor recovery system (Fig. 5) was added to the filter-press operation in 1991 to reclaim remaining hydrocarbons, specifically benzene, in the filter cake.
The system consists of a dryer, hot-oil system, conveying system, bulk nitrogen storage, oxygen analyzer, and closed-loop vapor recovery system. The conveying system has four components.
- A hopper sits below the filter press to hold the filter cake temporarily as it is dropped from between the plates.
- A screw conveyor, attached to the bottom of the hopper, then carries the "wet" filter cake to the dryer inlet.
- Another screw conveyor sits at the dryer discharge to carry the "dry" filter cake to a discharge bin containing large pans.
- The pans, designed to be moved with a forklift, are emptied periodically into roll-off dumpsters.
A hot-oil system provides the heat transfer fluid for the dryer. The system is designed to heat the filter cake to approximately 300 F. as it is conveyed through the dryer. This removes most of the remaining hydrocarbons from the filter cake, most importantly the benzene which has a boiling point of 176 F. at atmospheric pressure.
The dryer is purged with nitrogen during operation to ensure a nonexplosive atmosphere inside the dryer.
The oxygen analyzer monitors the dryer atmosphere and controls the nitrogen purge to maintain between 3% and 4% oxygen in the dryer.
If the oxygen level exceeds 7%, an alarm sounds and the hot oil is diverted from the dryer.
A bulk nitrogen storage system provides sufficient purge volumes.
A closed loop vapor-recovery system is attached to the dryer, and it consists of a refrigeration unit, condenser unit, and blower.
The blower system controls internal air flow and maintains the pressure inside the dryer at approximately - 1 in. of water to ensure that all vapors from the filter cake are contained within the system for recovery in the condenser unit.
The refrigeration unit consists of a chiller and two air-cooled coils to supply a 50/50 glycol/water mixture at 30 F. from the chiller and at 105 F. from the air-cooled coils to the vapor condensing unit. The hydrocarbon/water vapors from the filter cake are cooled from approximately 300 F. to 115 F., with the second stage cooling the vapor stream to 40 F.
The condenser unit contains a collection pot and sump pump with floats to control the liquid level. As the hydrocarbon-water condensate collects, it is pumped into the filter press' effluent stream which goes to the API separator. This piping arrangement allows the condensed hydrocarbons to be absorbed into the product present in the filter press effluent.
END-PRODUCT DISPOSITION
Operations at the reclamation facility separate the tank-bottom material into its three constituents: water, product, and solids.
The solids are captured in the filter cake. The product-water or "filtrate" stream from the filter press and the hydrocarbon-water condensate from the condenser unit are piped to an API separator where the product and water are separated and subsequently pumped to tankage.
The filtrate recovered from the filter-press cycle is a product-water mixture. Experience has shown that the filtrate is not an emulsified mixture and thus will readily separate.
A major benefit of tank-bottoms reclamation is the amount of product which can be recovered. WPL has been able to achieve a 20% recovery rate (that is, 20 bbl of product recovered for every 100 bbl of tank-bottom material processed). This recovered product can then be reblended into working storage or sold as fuel, depending upon its composition.
The effluent water recovered from the filter press is nonhazardous and can be discharged to the local sewer system for subsequent treatment. WPL has obtained a discharge permit from Kansas City, Kan., for the recovered effluent water.
The facility is designed to permit on site pretreatment of the effluent water if necessary in order to meet the discharge parameters established by the city.
The solids portion of tank-bottom material is trapped within the filter cake, a combination of diatomaceous earth, lime, and solids from the tank-bottom material.
Before the TC rule, the filter cake generated was dropped from between the plates into large pans placed beneath the filter press. The pans were then dumped into roll-off dumpsters for transportation and disposal at a local landfill as allowed by a waste-disposal authorization issued to WPL by the state of Kansas.
Lab analyses of composite samples of the filter cake ensured the material was nonhazardous before release of the dumpsters for disposal at the landfill.
Current operations are configured so that the filter cake is dropped from between the plates into a conveying system which carries the material through the dryer to the discharge bin which contains collection pans.
The "dry" filter cake is currently loaded into roll-off dumpsters for transportation and disposal at a local landfill utilizing the same testing procedures and disposal authorizations as were used before the TC rule.
With the dry filter cake being a nonhazardous material, testing is being done to determine if alternative uses might exist for the material. This would reduce the volume of material being placed into the local landfill and provide cost savings.
ENHANCEMENTS
Experience has indicated several areas where efficiency could be improved.
Continued research on filter-press plate configurations has yielded a system which differs substantially from the original design and provides significant improvement for filter-cake consistency.
The holding tanks have had mixers installed to prevent solids accumulation and to provide a more homogeneous feed to the filter press. Skimmer systems have been installed on the water tanks to allow easy removal of product if present.
A building for the filter-press trailer was constructed in 1989 to allow year-round operation. Along with the building, a tank-bottom material manifold with clean-out taps and transport unloading area was constructed.
As the facility expanded, all aboveground water and tank-bottom material piping had heat tracing installed to prevent freezing.
The most significant enhancement at the facility has been construction of the dryer and vapor recovery system in 1991. With this installation, the filter press was removed from the trailer and installed with the new equipment.
The design of the overall operation incorporated various changes made possible with the new equipment layout.
A major benefit of the dryer and vapor recovery system is the ability to reclaim "unpumpable" tank-bottom material with a high or heavy solids content. All tank-bottom material previously had to be "pumpable" by diaphragm pumps or it could not be received for reclamation.
Drum handling equipment and a special conveying system have been installed to allow efficient handling of unpumpable material which is received in 55 gal drums.
Handling the unpumpable material in this way helps to reduce the quantity of water previously used to clean a tank with heavy solids, which in turn reduces the volume of water to be discharged to the water-treatment facility. In addition, the tank-bottom material holding tanks are protected from the accumulation of these heavy solids.
OPERATIONAL CAPABILITIES
The reclamation facility currently employs six people: one manager, one supervisor, two process technologists, and two operators.
Depending upon the work schedule, this staffing allows WPL to reclaim between 3,000 and 4,000 bbl/month. One shift per week is allocated to perform preventive maintenance on all equipment.
A PC-based data base system is used to log filter-press operations data, monitor inventories, and track water, filter cake, and reclaimed product.
Operations, which were seasonal from 1985 through 1989, have been year-round since 1989 when the location was "winterized."
Approximately 150,000 bbl of tank-bottom material have been reclaimed since start-up in 1985. Annual volumes received at the facility have ranged from 3,000 to 22,000 bbl of material generated within the WPL system along with an additional 8,000 to 15,000 bbl from third-party generators.
Additional throughput capacity can be realized with the addition of another shift which enables a 24-hr operation.
Copyright 1993 Oil & Gas Journal. All Rights Reserved.
