Advanced technologies seal in emissions, safety and reliability BY JOSEPH J. T R ~

U M p SEALING WITH ZERO FUGITIW EMISSIONS AND

1,000 percent greater mean time between planned P maintenance (MTBPM) becomes affordable with advanced technology mechanical seals. These new seals eliminate the need to replace pumps and related components with less economical, seal-less pumps, re- gardless of how smct emissions regulations, enforcement practices and monitoring re- quirements become.

More companies are benefiting from new seahg technologies through retrofits; for example:

A refinery achieved a 10-fold emissions reduction in propane services - 1,000 ppm to 100 ppm - with a low-emissions, single seal and segmental bushing;

Another refinery lowered emissions to less than 100 ppm in a stabilizer reflux pump

handling light hydrocarbons by using a low- emissions, single seal;

A third refinery installed segmental bushings for secondary containment throughout the facility after a bushing pre- vented a potentially catastrophic gasoline leak, and

A chemical plant increased reliability by installing non-contacting, dry-running, dual- camidge seals in a cellulose acetate process. (Old seals were changed every three weeks; new seals have lasted more than 14 months with zero emissions.)

To ensure zero emissions and uninter- rupted safety in the event of upset conditions at the inboard seal, another chemical plant uses a combination of new and traditional technologies in a dual-seal arrangement to support an elbow pump circulating volatile reactants in a vessel. This sealing system en- sures zero emissions during normal dynamic operation and will contain all leakage in the reactor bag in the event of a process mal- function. The system operates in extreme service conditions - isobutane flush a t 1,100 pounds per square inch gauge (psig), mineral oil barrier at 1,200 psig, speed of 2,400 revolutions per minute (rpm) and tem- perature a t 200 degrees Fahrenheit. The dual-seal arrangement includes:

A balanced O-ring, pusher-type in- board seal with reverse pressure capabilities;

Segmented bushing; and A dry-running, non-contacting out-

Advanced technological accomplishments board seal.

66 HAZMAT WORLD JULY 1993

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by seal man&cturers come at a critical point in time. EPA has established baselines for judging chemical processing plant emissions compliance, and the Agency later this year plans to issue emissions control d e s for pe- troleum refining. In addition, OSHA has es- tablished compliance deadlines for meeting process safety management requirements for hi& hazardous chemicals (HHG).

Containment, not just control. Ad- vanced seal designs focus on emissions con- tainment, not just control, and can con- tribute significantly to equipment reliability and productivity. This is particularly impor- tant because reliability, safety and emissions containment are closely l i e d . Seals con- sidered “poor performers” today were not failures a few years ago, according to previ- ously accepted leak rates.

Zero- and virtual zero-emissions levels for safety and environmental pqotection

ment and long-term secondary seal reliabili- ty if the primary seal malfunctions.

Increasing burden. Process and main- tenance engineers face m y e burdens than their predecessors. With nearly endless seal- ing options, engineers must consider EPA and OSHA regulatory requirements, as well as improving productivity and reducing waste. Government concern over potential- ly adverse effects of pollutants, public de- mand for environmental cleanup and acci- dental environmental damage from toxic

substances have prompted regulation of roxic air pollutants in the form of control programs, strategies and rules developed by federal, state and regional agencies.

EPA’s air toxics program - a national strategy for reducing risk posed by haz- ardous air pollutants - has been expanded, giving more regulatory responsibilities to state and local governments. (Air toxics problems have been addressed under such statutes as SARA Title III, RCRA, TSCA, CWA and CAA Section 112.) The 1990

With nearly endless seal- ing optrons, engheers must conslder aPfi and OSM regulatury requbements, as well as lmprovlng productrvnty and reducing waste.

over ext$ded peri- ods are‘assured by new developments in single seals, sin- gle seals with sec- ondary contain- ment devices, con- tainment seals to convert “wet” tan- dem arrangements to dry sealing, and complete dry-run- ning seal system

nologies extend seal operating life. Non-contacting and full-face con- tact dry seals, in particular, impact

uids by enhancing containment while

designs. These tech-

sealing pumped liq-

simplifying and reducing compliance costs, and inaeasing MTBPM.

For example, a chemical facility installed non-contahg, dry-running, dual-cartridge seals when developing its maximum achiev- able control technology (MACT) compli- ance strategy. Product purity requirements ruled out wet double seals with American Petroleum Institute’s (Washington, D.C.) Plan 53 support, and mag-drive pumps could not satisfy phenol condition require- ments. The results were zero emissions and continuous reliability. Similar benefits are being realized by another chemical plant that installed 22 zero-emission seals.

Dry containment sealing was a solution for a major refinery‘s hydrofluoric alkylation unit. An inboard O-ring, pusher-type seal with reverse pressure capabilities is support- ed by a segmental safety bushing and a dry- running, spiral groove containment seal. A safe nitrogen purge is used. The arrange- ment assures complete emissions contain-

Circle No. 331 on Reader Service Card HAZMAT WORLD JULY 1993 67

Pumps and seals CAA Ame”n ts require EPA to broaden its approach to regulate source categories for 189 toxic air pollutants and establish MACT standards for each source category.

Three phases of control standards will p v e m hazardous chemicals and VOCs in chemical processing. During the first two phases, the Agency must implement a leak detection and repair program, with greatly reduced leak definitions appearing in the second phase (See Chart A, Page 69). Some regions have much stricter regulations than

are planned under federal rules. In the third phase, periodic monitoring

will be coupled with a base performance level for entire facilities. The base will be

-the average of the best 12 percent perform- ing facilities in the source category - a level against which all chemical processing plants in that category will be measured.

Facilities achieve compliance through good maintenance and operation proce- dures, says Tom Kittleman, a senior con- sultant with E.I. du Pont de Nemours &

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Co. Inc. (Wilmington, Del.). MACT is a work practice, he explains. “It’s a quality control program with built-in penalties and rewards.”

Penalties for not complying with the base requirement and failing to report haz- ardous substances releases will range from more frequent monitoring to EPA-imposed fines of up to $25,000 per day. Compliance rewards include less frequent monitoring - a cost incentive for any company.

speci i ing equipment. Questions en- gineers must ask when specifjmg equip- ment for a new plant, upgrading for a plant

Spiral p e technology applied t 0 p n x e . s ~ ~ elimi- nuts fugitive ernixiuns, pmvider high kvek $@q a n d ~ m a n ~ b e t w e m p h n e d ~ ~ ~ 1,000penent and“

expansion or maintaining an existing unit include:

What is the emissions factor in pounds per day?

Will the system meet specified emis- sions rates?

Does the seal system have experience at pressure, temperature, flow and power requirements?

What is the first cost? What is the iife-cycle cost? What is the predominate failure mode,

and what happened? What happens in the worst-case failure

situation? Maintenance engineers may obtain in-

formation from federal, state and local agencies and regulations; industry associa- tions and societies; and seal manufacturers. However, using Synthetic Organic Chemi- cal Manufacturers Institute (SOCMI; Washington, D.C.) emissions factors to es- timate fugitive emissions may result in over- estimating emissions by as much as a kctor of 10, or even 100.

CirCe No. 353 on Reader Sewice Card 68 HAZMAT WORLD -JULY 1993

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Society of Tribologists and Lubrication Engineers’ (Park Ridge, Ill.) document SP- 30 is considered an excellent reference for selecting mechanical seals to meet specific emission rates (See Chart B, Page 70). This document, which contains guidelines for meeting emissions regulations for rotating machinery with mechanical seals, shows ex- isting technologies can satisfy CAA emis- sions control requirements. By selecting a seal in Area 2 of the chart, for example, en- gineers can ensure the seal will hold emis- sions to less than 1,000 ppm under these conditions:

Less than 6 inches in shaft diameter; At pressure less than 600 psi5 For surface speeds up to 5,600 feet per

In a specific gravity greater than 0.4. A 96 percent emissions reduction can be

realized by upgrading from a single seal in a stuffing box (originally designed for pack-

minute; and

ing) to a low-emissions, single seal in a seal chamber.

Mandated safety. For the most severe carcinogenic fluids, such as benzene and bu- tadiene, OSHA accepts zero-emissions lev- els only.

Engineers also must comply with OSHA’s process safety management of HHCs. Potential trouble spots with these chemicals must be identified and corrected through retrofit or replacement projects, and OSHA requires documentation. A 25 percent completion rate is mandated by May 1994, with additional 2 5 percent com- pletion targets in each of the following three years.

Sealing technology can meet these re- quirements. A plant-wide retrofit at an eth- ylene production facility, for example, satis- fied safety goals through upgraded sealing of 27 hazardous service pumps, using tan- dem and double-seal arrangements [O-ring,

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Circle No. 340 on Reader Service Card HAZMAT WORLD - JULY 1993 69

Pumps and seals polytetrafluoroethylene (PTFE) wedge and metal bellows]. One year after the retrofit, leakage tests demonstrated no pump had more than 100 ppm emissions at the out- board seal, and many continued at the zero- emissions level (See Chart C, Page 71).

Compliance made easier. Advanced technology seals help meet regulatory re- quirements while maintaining productivity and efficienq.

Single seals Figure 1, Page 72), for low emissions performance, provide up to three

years of emissions control at less than 500 ppm; 70 percent of these seals limit leakage to 30 ppm or less, according to an industry study. The seals offset the combined effects of pressure distortion and heat generation on leakage and wear. A computer-modeled design optimizes face designs and materials selection to ensure stability.

Added safety is provided through a seg- mental bushing that offers positive leak protection, preventing mass escape of process fluid if a primary seal malfunc-

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Sprung's dedication to quality and service is backed by the industries largest guarantee program. We challenge anyone to meet the quality of the Sprung Instant Structure and to match our record of service and prompt delivery. Offices are located worldwide to help you solve your shelter needs. Installations of Sprung Instant Structures are supervised by professional Technical Consultants supplied by the company. Lease or Purchase plans available.

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dons. Bushings also can be used in multi- ple seal arrangements and with a broad range of seal types, such as O-ring, polyte- trafluoroethylene wedge, and elastomer and metal bellows.

Near-zero emissions levels may be ob- tained for a single seal by adding a full-con- tact, dry-running containment seal (Figure 2 , Page 72). Leakage from the primary seal is captured and sent to the flare or vapor-re- covery system. This type of containment seal can replace the outboard seal when converting from an existing liquid-lubricat- ed tandem arrangement to dry sealing.

Multiple seal arrangements with appro- priate support systems - tandem, double and gas-lubricated, non-contacting, dry- running seals - ensure emissions contain- ment at any level. A tandem amidge seal consists of two seals, between which a buffer fluid operates at a pressure less than the pump process pressure. The buffer fluid iso- lates the process liquid from the atmosphere and is maintained by a support system.

A double-cartridge seal arrangement has

Circle No. 346 on Reader Sewice Card 70 HAZMAT WORLD - JULY 1 9 ~ ~

Chart C. Ethylene production plant emissions one year after startup (MACT compliance guidelines - 1,000 ppm for each pump)

two seals operating in a barrier fluid main- tained at a pressure higher than the process fluid. It is made operational by a properly matched and sized support system and ex- temal pressure source.

The newest achievement in multiple seal arrangement is the dry-running, non-con- t a h g double-caraidge seal (Figure 3, Page 72), assuring zero emissions of process fluid. This gas-lubricated seal arrangement ex- tends MTBPM at least 10 times, with no threat of product contamination from pres- surized buffer liquids. Clean, dry, buffer gas, such as plant nitrogen, is injected into the seal chamber at 20 to 30 pounds per square inch above the process pressure. The only minimal, controlled leakage to the atmos- phere is inert nitrogen. The support system for this dry-running seal arrangement costs less than one-&urd of a typical, pressurized wet seal support system.

Evolving levels of manufacturing exper- tise allow seal suppliers to help pump users meet emissions containment, safety and reli- ability requirements, no matter how strin- gent they become.

Computer programs, evaluation process- es and testing systems help bring new levels of expertise to seal design and performance. A range of customized software removes guesswork from application-specific seals before designs leave the laboratory. Soft- ware assures design integrity by predicting the performance of interrelated seal-face fluid film variables, by identifjmg causes of

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Circle No. 347 on Reader Sewice Card HAZMAT WORLD JULY 1993 71

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Circle No. 338 on Reader Service Card 72 HAZMAT WORLD -JULY 1993

Figure 1. Type 48 low-emissions single seal t

t f Figure 2 Type 48 single seal and type 48SC dry-running secondary containment seal

k

Figure 3. Type 2800 gas-lubricated, dry-running double seal

- - t - Pumps and seals - seal malfunctions, and by minimizing design time requirements.

Design methodologies are enhanced further by better understanding of the in- trinsic properties of seal-face materials - one of the most critical factors contributing to predictable, repeatable performance. Materials selection now is considered to be as important as the seal design itself. Test-

ing capabilities can verify performance in actual services using EPA 21 test method- ologies, or they can “bag” for mass emis- sions to prove a pump’s or seal’s perfor- mance before installation. v

Joseph 3. T+ytek is a vice pr&t at John Crane Inc. (Morton Grove, Ill.), a worldwide manufnmcrer of engineered sealing ystm.

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