TECHNOLOGY, EFFICIENT OPERATION KEY ELEMENTS IN ENVIRONMENTAL STRATEGY

Anne K. Rhodes
Refining/Petrochemical Editor

Refiners around the world are facing difficult environmental challenges-reduced emissions to air, water, and land; reduced lead, benzene, sulfur, and vapor pressure in gasoline; and reduced sulfur and increased cetane number for diesel fuels.

The first round of U.S. fuel regulations mandating oxygenated gasoline and low-sulfur diesel is behind U.S. refiners. But while they are busy building to meet 1995's Reformulated gasoline requirements, and refiners in most countries are preparing to reduce or eliminate lead from their fuels, myriad investments are required to reduce plant emissions.

As a result, refiners are assessing the impact of current and future regulations, calculating the costs of complying with them, and studying new technologies for meeting them.

AIR EMISSIONS

The U.S. Clean Air Act Amendments of 1990 (CAAA) contain several titles that will require refiners to further reduce air emissions from stationary sources. These requirements include mandated equipment modifications and enhanced inspection and maintenance (I&M) programs to reduce fugitive emissions from such sources as valves, pumps, and compressor seals.

Title 1 of the CAAA requires areas that fail to meet national ambient air quality standards for certain pollutants to reduce emissions. States must submit state implemention plans addressing reduction of the appropriate pollutant for each nonattainment area.

Title 3 of the CAAA identifies hazardous air pollutants (HAPS) regulated by the U.S. Environmental Protection Agency (EPA) under the national emissions standards for HAPS, or Neshap. Title 5 required states to submit permitting plans to EPA by Nov. 15 of this year. These plans are subject to agency approval.

The National Petroleum Council (NPC) undertook a study to determine the impacts and quantify the costs of environmental regulations affecting refiners. In its contribution to the NPC study, Bechtel Corp. listed process units and systems that are the principle sources of air emissions from refineries (Table 1).

Adding to these costs will be the addition of high-efficiency electrostatic precipitators (ESPS) to control particulate matter (PM) from fluid catalytic cracking (FCC) units. Bechtel projected that ESPs eventually will be installed on every FCC unit in the U.S. that does not already have this equipment.

Coker operation and coke-handling systems will also require control to reduce PM. Enclosed conveying and storage will be the system of choice to control particulates containing metals classified as HAPS, according to the Bechtel study.

Also contributing to refinery costs will be the control of carbon monoxide (CO) emissions, accomplished by efficiently operating existing equipment such as CO boilers and process heaters. Because most FCC units in the U.S. have CO boilers, capital requirements will be minimal. In the Los Angeles area, however, CO emissions may require additional control.

The Bechtel report adds that stringent NOx reduction via combustion controls (as part of the ozone attainment strategy) will increase CO emissions. These added emissions may require control through the use of post-combustion devices such as catalytic incinerators.

Regulations governing fugitive emissions from equipment leaks will require an aggressive inspection and maintenance program. Limits for leak repair are expected to be 500 ppm initially and capital costs will include buying portable analyzers and computers and attaching identification tags on the thousands of points requiring inspection. California leak-repair limits, however, may eventually be as low as 100 ppm, says Bechtel, making adjustments to leaking components more costly.

Table 2 shows Bechtel's estimate of the capital costs required to meet air emissions requirements. Table 3 shows the projected reductions in air emissions through 2010, attributable to these tighter controls.

WASTE WATER

In the waste water sector, the principle cost to refiners will be encountered in the reauthorization of the Clean Water Act (CWA). Stormwater, groundwater, and process water issues will also play a major role (Table 4).

Bechtel outlined three steps to optimizing process water reuse in the coming years:

• The addition of filtration after the two-stage activated sludge biological treatment using powdered activated carbon (PACT).

  This filtration would also be required to satisfy the anticipated requirement to minimize discharge of suspended solids. The installation of tertian,-treatment filters is anticipated in 75% of all U.S. refineries by 2000 and 100% by 2010.

• I:se of reclaimed process waste water that had received tertian, treatment as cooling-tower makeup. This reuse is anticipated in 75% of U.S. refineries by 2000 and 100% by 2010 because, once the filters are installed, minimal additional equipment will be required to utilize the reclaimed water as cooling-tower makeup.

• Use of sidestream softeners and filters to treat cooling-tower blowdown will be the next reuse stage. These systems control the concentrations of silica and "hardness" salts, the solubilities of which limit the cycles of concentration in the cooling tower and associated heat-transfer equipment. Installation of cooling tower sidestream treatment systems is anticipated in 50% of U.S. refineries by 2000.

Fig. 1 illustrates several proposed process and stormwater collection and storage systems. These systems may be installed to minimize contaminated water requiring treatment and maximize uncontaminated stormwater flowing to a permitted stormwater outfall.

The proposed treatment systems to handle contaminated process and stormwater are shown in Fig. 2.

SOLID WASTES

A number of regulations are driving the hazardous and nonhazardous solid waste sector:

• Groundwater issues-Monitoring and pollution prevention.

• Above-ground storage tanks-Replacement of older tanks, installation of double bottoms and/or double seals for light and heavy hydrocarbon tanks.

• Reauthorization of the Resource Conservation and Recovery Act (RCRA)-New waste streams are likely to be listed.

• RCRA toxicity characteristic land disposal restrictions -Most RCRA surface impoundments will be closed or retrofitted to meet RCRA minimum technology requirements by 1995.

• RCRA corrective action-Remediation of contaminated soil and monitoring of solid waste management units used to manage nonhazardous wastes.

• Comprehensive Environmental Response, Compensation, and Liability Act-Possible loss of exclusion could subject the refining industry to involvement in cleanup anywhere refinery waste has been disposed of in the past.

Table 5 totals the costs of solid waste control technologies for refiners.

NEW TECHNOLOGIES

Now that the current and future regulatory climates have been described, a brief overview of a few new technologies for meeting some of these requirements is in order. Because the scope here is too limited to allow a comprehensive analysis of state-of-the-art technologies, the activities and processes of only a few companies will be presented.

FLUID-BED BIOREACTOR

Common cleanup methods for contaminated Groundwater involve physical or chemical processes, such as air stripping or carbon absorption. But when the quantity of affected groundwater is large and levels of contaminants like benzene, toluene, or xylenes are high, an alternative method is needed.

Shell Internationale Research Mij. B.Y. has developed such an alternative in its "fluidized-bed biological reactor" process. The system uses a fluidized bed of solid particles to provide extensive surface area for the growth of hydrocarbon-degrading microorganisms.

Contaminated water flows through the reactor and the contaminants are absorbed, degraded, or both, on the surface of the particles. The flow rate can be adjusted to ensure proper decontamination levels.

ROG EMISSIONS CONTROL

California's South Coast Air Quality Management District (Scaqmd) requires that discharge from process pressure-relief valves (PRVs) in hydrocarbon service be directed to a closed system (such as the fuel gas system, firebox or flare).

ARCO Products Co. was facing an estimated $7.7 million cost to upgrade the existing relief system at its Los Angeles refinery to handle the design relief loads. But Bechtel Corp. developed a design to achieve emissions of reactive organic gases (ROG) commensurate with Scaqmd guidelines for $1.5 million.

API codes require that pressure vessels be provided with overpressure protection. Each of ARCO's two naphtha dehexanizer towers is provided with two PRVS. One is installed for protection in the event of a fire and is routed to the flare system. The other-designed to handle much larger process-upset loads-is routed directly to atmosphere. It was this PRY that required equivalent control technology (ECT) to meet Scaqmd guidelines.

Using a source-reduction philosophy, the Bechtel plan reduced the probability of an overpressure condition to a sufficiently low level. This prevented the PRY (theoretically) from ever having to relieve over the design life of the process unit.

The dehexanizer relief system was designed with three emissions-controlling features:

• Increased operating margin

• A steam automatic lockout system

• A rupture disk for fugitive emissions control.

With a flare destruction efficiency of 98%, annual uncontrolled ROG emissions would have been about 2,027 lb/year. But with the ECT design, estimated emissions will be approximately 11 lb/yr. Scaqmd accepted the proposal, saving ARCO $6.2 million.

FLUE GAS DE-NOx

Shell Research has also developed a novel technology for removing NOx from flue gases and other streams. The add-on process - called Shell Denox - can remove NOx at lower temperatures, as compared to conventional NOx-removal technologies (120-350 C. vs. 300-400 C.).

Shell's Denox catalyst system is effective at these lower temperatures, which are more compatible with typical flue gas temperatures (150-200 C.), says Shell. The high-activity catalyst, containing titanium and vanadium compounds, and the low-pressure-drop reactor achieve the lower temperature NOx removal.

Shell says the system can be added to the end of a process during normal shutdown procedures. And it can be adapted to a wide range of applications, including flue gases from gas turbines, gas-fired heaters, and boilers.

The reactor design allows for fast catalyst loading and discharge. This is important when treating streams containing high levels Of SO2 and dust, which can deactivate a catalyst quickly.

The first commercial Denox unit was installed in a German petrochemical plant in 1989. Since then, the process has been applied to industrial furnaces and processing plants in Europe and the U.S.

SPENT CATALYST

The production of spent refining catalysts is on the rise. Many of these catalysts contain heavy metals such as cobalt, nickel, and vanadium, and during use, they become contaminated with carbon residue and heavy metal oxides and sulfides.

This contamination can pose a fire hazard during handling and storage. In addition, toxic components can be leached in landfill sites. To avoid these hazards, many refiners are sending catalysts out for metals reclamation.

Shell Research has developed a method for recovering the metals for sale while rendering the remaining slag environmentally stable. (It should be noted that many other companies also have metals-reclamation processes.)

In Shell's new process, the waste is smelted with a reductant (coke) in the presence of a collector metal (scrap iron) and lime. This process takes place in a plasma arc furnace.

The coke reduces the metal oxides, and the metals are collected as an iron alloy. The alloy is suitable for resale as steel alloy or as scrap. The ceramic carrier contained in the catalyst combines with the lime to produce a cement-like slag with a very low metals content. This slag can be used as building material or disposed of as industrial waste.

Shell says the new process can handle most types of spent catalyst, even at relatively low throughput rates.

OTHER TRENDS

Refinery waste water treatment facilities are more frequently being built aboveground as tank-based units, says Don Vacker of Bechtel Corp. Most tanks are equipped with double bottoms or grooved concrete foundations to provide a leak-detection system, although regulations do not require it at this time.

Several Bechtel clients are also requiring sewers to be placed in concrete trenches to preclude groundwater contamination, especially where listed wastes are handled, says Vacker. Pipes carrying waste water or non-listed wastes are now run on pipe sleepers or racks when possible.

Refineries are also leaning toward building aboveground API separators, dissolved air flotation units, equalization tanks, and aeration tanks. Most new clarifiers also are being built out of the ground, with sloped concrete bottoms at ground level.

Aeration tanks are being built routinely with 20 ft or more of water depth, says Vacker, and 40 ft is not uncommon. Clarifiers too are being built to increasing depths for greater effectiveness (water depths are routinely 15-18 ft).

EFFICIENT OPERATIONS

Another important consideration in reducing emissions is pollution prevention, or waste minimization. Donald B. Anthony, Bechtel's vice-president and manager of technology, says: "Preventing the creation of waste will be the environmental focus of industry in the 1990s and the early part of the 21st century."

There are opportunities for waste reduction in any process plant, says Anthony. Changes in operating procedures and housekeeping can certainly help, but ultimately these efforts will be limited by the design itself.

In his address at Bechtel's Environmental Challenges Briefing Sept. 14 in Houston, Anthony named several major companies that have highly visible programs for reducing wastes:

• 3M Corp.'s program is called PPP, or pollution prevention pays.

• Chevron Corp. has the Smart program, or save money and reduce toxics.

• Dow Corp.'s program is called WRAP, for waste reduction always pays.

• Union Carbide Corp. has the WMOR program, for waste minimization opportunities review.

Anthony characterizes such programs as being based on a "total quality management" approach. Such programs, he says, have eliminated millions of pounds of pollutants from manufacturing processes, saved substantial sums of money, and improved efficiency of production processes. Side benefits include improved product quality, enhanced public perception, and improved employee morale.

Chevron's Perth Amboy refinery developed such a facility-wide pollution prevention initiative, said Anthony. Cross-functional teams identified more than 300 opportunities for improvement, citing 10 items requiring immediate action.

Pollution prevention is particularly attractive because it can be achieved without large capital investments, in some cases. And in this era of scarce capital and increasing regulation, that can put an operator at a competitive advantage.