METHOD FOR CONTROLLING THE EMISSIONS FROM A SLOT TYPE COKE OVEN

Abstract: A method for controlling door and stack emissions from a slot type coke oven. A clean, neutral or nonoxidizing gas under pressure is introduced into a gas chamber (18) in the coke oven door (1) formed between a pair of door seals (11) on the coke oven door. The coke oven gases inside the oven in the vicinity of the coke oven door are allowed to flow freely in a vertical direction to reduce the pressure variability against the inner door seal. The collecting gas main pressure is maintained substantially equal to or less than the pressure at the top of the heating flue of the oven.

Description: METHOD FOR CONTROLLING THE EMISSIONS FROM A SLOT TYPE COKE OVEN Background of the Invention This invention relates to a method for eliminating the emissions from the doors and stacks of slot type coke ovens. Fugitive emissions coming from the doors and stacks of slot type coke ovens has been a problem facing coke producers since the first instal¬ lation of slot type by-product coke ovens. In recent years, stringent environmental laws and regulations have required coke producers to spend many millions of dollars on new ideas and equipment in attempts to reduce these emissions to an acceptable level and to comply with the environmental laws and regulations. While some of these new ideas and equipment have helped to reduce the amount of emissions, none have been able to eliminate the emissions altogether or to reduce them to environmentally acceptable levels. Summary of the Invention The object of this invention is to provide methods and apparatus for eliminating emissions from the doors of slot type coke ovens and to significantly reduce the emissions from the stacks of slot type coke ovens during the coking cycle. A further object of this invention is to provide methods and apparatus to eliminate or greatly reduce coke oven door and stack emissions that can be easily installed or used with existing coke oven batteries and thereby allow existing batteries to operate in a clean and environmentally acceptable manner. It has been discovered that the above objectives can be obtained by introducing a clean, neutral or nonoxidizing gas into a gas chamber formed around the periphery of the coke oven door between a first sealing means and a second sealing means, allowing the coke oven gases located in the coke oven adjacent the inside of the coke oven door to flow freely in a SUBSTITUTESHEET vertical direction within the oven adjacent to said door, and by maintain¬ ing the' collecting gas main pressure substantially equal to or less than the pressure at the top of the heating flue of the oven. Brief Description of the Drawings FIGURE 1 is a schematic sectional view of a coke oven door modified to be used in accordance with this invention. Detailed Description of the Invention This invention involves the synergistic combination of apparatus and methods to a slot type by-product coke oven battery to effectively control or eliminate fugitive emissions coming from the doors, walls, roof and stacks of the coke oven battery. The first cooperative element of this invention is the modifica¬ tion of the standard coke oven doors to include a neutral gas chamber as shown in FIGURE 1 and described below. FIGURE 1 illustrates a schematic cross-section of a typical coke oven door which has been modified according to one embodiment to this invention to include a neutral gas chamber. The door 1 comprises a steel door frame 2, a door latch assembly 3 which closes the door against a steel door jamb 4. The steel door jamb 4 is secured to and interlocks with a refractory block door jamb 5 set into the refractory end wall 7 of the coke oven. The use of refractory block 5 instead of the usual one piece heavy steel door jamb greatly reduces the tendency of tar build-up on the jamb. The steel door jamb 4 is further secured in place by steel clamps 8 which engage a recess in the steel door jamb 4 and a flange of the steel buckstays 9. A first sealing means 10 comprising a spring loaded thin knife edge 11 which engages a flat surface 12 of the steel jamb 4 extends around the entire periphery of the door 1 and provides a substantially gas tight primafy seal when the door 1 is in place and closed. A second sealing means 13 comprising an L-shaped arm 14 secured to the steel door frame 2 has a gasketed surface 15 which bears against a flat surface 16 of the steel jamb 4, also extends around the entire periphery of the door 1 and provides a gas tight secondary seal when the door 1 is in place and closed The space between the first sealing means 10 and the second sealing means 13 and between the steel door jamb 4 and the steel door frame 2 comprises gas tight chamber 18 for holding a clean, neutral or nonoxidizing gas at a pressure slightly greater than the oven pressure, as will be described below. It should be noted that coke oven doors having a gas chamber hav been tried before. U.S. Patent No. 4,067,778 to VanAckeren, et al. and German Patent No. 1,156,762 to Didier-Werke A.G. both describe coke oven doors having a chamber for holding coke oven gas which is then allowed to flow Into the coke oven to discourage door emissions and be consumed in th coking operations. According to our invention, the chamber 18 will be preferably filled with a clean, neutral gas, such as nitrogen, by conduit 19 and valv 20 at a pressure slightly higher than the pressure inside the coke oven. With this positive differential pressure in the door gas chamber 18 any leakage through the first or inner sealing means 10 will be from the door gas chamber 18 into the oven. Any leakage from the gas chamber 18 through the second or outer sealing means 13 will be clean, neutral gas and not flammable, dirty coke oven gas. Successful operation of any coke oven door depends on minimizing leakage. All coke oven door seals can be expected to have some leakage. With the door gas chamber 18 at a higher pressure than either the oven or the atmosphere, and leakage, however slight, whether into the oven or into the atmosphere will be clean, neutral or nonoxidizing pressurizing gas, not dirty coke oven gas. However, if leakage through the door's outer seal 13 is too great, it will be impossible to maintain adequate neutral gas pressure in the door chamber 18 and coke oven gas could possibly pass seal 13 and leak to the atmosphere. Even if there were no coke oven gas emissions, exces¬ sive leakage of neutral gas would increase operating costs. On any door the differential pressure across its seal is the primary factor affecting the amount of gas leaked. Therefore, another purpose of the present invention is to minimize that differential pressure thereby minimizing leakage. In order to decrease the differential pressure across the inner seal 10 while maintaining the door gas chamber 18 above oven pressure it is necessary to reduce the variability of gas pressure against the inner door seal 10 from inside the oven. The second cooperative element of this Invention is therefore the further modification of the standard coke oven door to provide for a substantially uniform internal oven pressure around the periphery of the Inner door sealing means 10. The coke oven door 1 as shown in FIGURE 1 contains a refractory door plug 25 which insulates and protects the steel door 1 from the coke (coal) mass in the oven. In most coke oven doors the refractory door plug is bolted directly to steel door face plate 26. As shown in FIGURE 1, the door plug 25 of the present invention is spaced and positioned inwardly of the steel door face plate 26 and insulation pad 30 by steel channels 27 thereby creating a vertical flue or duct 28 extending from the bottom to the top of the door just inside the oven door 1. Without a flue or duct 28, the oven gas pressure on the inside of the inner sealing means 10 would be much higher at the bottom of the door than at the top of the door especial¬ ly just after the oven has been charged with coal. The flue or duct 28 also relieves excess pressure of any pockets of coke oven gas created in the oven which would otherwise be trapped between the door and the coke (coal) mass. The use of a door plug arrangement of this invention greatl reduces variability of pressure at the inner door sealing means 10 with t oven. In turn, the differential pressure necessary to keep the door gas chamber 18 at a positive pressure relative to the duct 28 is minimized by reducing pressure variability within the oven as described above. This minimum differential pressure in the door gas chamber 18 greatly reduces the gas pressure required in chamber 18 and the tendency for any neutral gas to leak from the door gas chamber 18 into the oven or out int the environment. While coke oven doors having vertical flues or ducts in the doo plug have been used before, the flues and ducts were used to convey the coke oven gases from the bottom of the oven to the top of the oven where these gases were then drawn off into a collection main. U.S. Patents 4,086,145; 4,381,972; 4,414,072 and 4,422,902 describe door plugs of this type which are used to remove the coke oven gases from the oven in the vicinity of the door. An important factor to be considered in operating a door of thi invention is the excessive loss of the clean, neutral gas to atmosphere. As described above, the outer sealing means 13 could have some leakage. The differential pressure across the door's outer sealing means 13 is the factor determining the amount of neutral gas that leaks to atmosphere. T preferred door gas chamber 18 pressure is the sum of the oven pressure an the differential pressure across the door inner sealing means 10. With t differential pressure minimized, the required door gas chamber 18 pressur of the neutral gas can be further reduced by also reducing the pressure inside the coke oven. Therefore, the third cooperative element of this invention is to significantly reduce the oven operating pressure. This has not been practical with the present configuration of equipment. The prior art practice was to operate ovens at an oven pressure sufficiently high so that the bottom of the oven door is not negative relative to atmosphere at any time during the coking cycle. Because thermal lift affects gas inside the oven during the latter part of the coking cycle, the pressure at the top of the oven became significantly greater as ovens were made taller. A six meter high oven is normally operated with a pressure of 12 to 20 mm water column at the top of the oven so that the pressure at the door bottom does not go negative. This is done so that any door leaks will be outward, from the oven to atmosphere rather than vice versa to prevent damage to the oven refractories from oxidation by the influx of air. This outward flow of coke oven gas is to some degree self-sealing because tar from the leaking coke oven gas condenses on the door and jamb thereby forming its own tar seal. However, such outward flows cause undesirable and environmentally undesirable coke oven gas door emissions. If an existing oven Is operated at a low collecting gas main pressure, the tar seal will not develop. Pressure at the door bottom will go to a negative pressure (below atmospheric) during the last part of the coking cycle and ambient air will be drawn Into the oven. The incoming air will result in rapid heat generation and the rapid oxidization of silica brick used to line the ovens. The result is premature oven refractory failure requiring a rebuild costing many millions of dollars. For example, present six meter coke batteries cannot be operated with collecting gas main pressures below approximately 10 mm water column. With the present invention, however, the collecting gas main pressure is maintained equal to or less than the pressure at the top of the combustion or heating flue in the oven. Normally flue top pressure in the oven is about 4 mm water column, depending on the battery, so the oven according to this invention would be operated at less than 4 mm water column. This low oven pressure, at or near equilibrium with that in the heating flues, reduces to near zero the differential pressure and avoids raw coke oven gas from the oven chamber leaking into the heating flues and then cracking to form soot which is discharged out the stack. The door gas chamber combined with the above described low pressure oven technology will permit the gas chamber 18 between the seals 10 and 13 to be pressurized with a clean, neutral gas at a relatively smal positive pressure (several mm water column) above oven pressure. This small differential above oven pressure will insure that any leaks will be through the inner door seal 10 into the oven and such leaks will be a clean, neutral or nonoxidizing gas going into the oven and not a dirty, flammable gas going out into the atmosphere. This invention also insures that only a clean nonoxidizing or neutral gas can leak into the oven. Suc a gas will not damage the oven refractory or be a detriment to the coking process, as would air. Since the door gas chamber 18 is pressurized with clean, neutral or nonoxidizing gas the outer sealing means 13 on the door does not have to resist the raw coke gas containing tar, coal chemicals an other dirty solids. With the low pressure operation of this invention and improved physical location, leakage through the outer sealing means 13 is minimized. This seal also sits against a relatively cool, clean area on the steel door jamb 4. Using the above example, with the pressure at the top of the heating flue at 4 mm water column the collecting gas main pressure will also be 4 mm water column and the door gas chamber 18 pressure will be about 6 mm water column, according to this invention. On a conventional SUBSTITUTE S prior art oven the door is required to seal against a collecting gas main * pressure of 12 mm water column or more. Individually, there are fundamental design and operating problems with each of the three elements proposed for the control of coke oven door emissions. Used in concert, however, these elements react synergisti- cally to solve the problems. In this unique combination they completely eliminate coke oven door emissions and greatly reduce coke oven stack emissions. For example, the prior art coke oven gas filled door chamber such as in U.S. Patent No. 4,067,778 is difficult to keep clean and, at the normal high coke oven operating pressures, the loss of coke oven gas from the chamber could be excessive. Under those operating conditions pressur- ization of the chamber would be difficult to maintain and, if door chamber gas pressure is lost, the door becomes ineffective. The ventilated door plug used by the prior art somewhat assists door seal cleaning problems. Experience has shown, however, that coke oven gas passing through the ventilated plug increases the temperature of the sealing surface thereby reducing tar condensation. This lack of fresh tar (an elastic sealant) on the door seals makes their fit requirements exact- ing. As a result, doors with a ventilated plug must be better adjusted to avoid these leakage problems. The present invention will insure that any leaks are only clean, neutral gas and therefore tar normally carried onto the jamb and seal by leaking dirty coke oven gas is eliminated. While some might argue that just lowering oven pressure is a simple method for reducing door emissions, such a practice results In rapid destruction of the oven refractory through air infiltration into the oven causing rapid oxidation of the silica refractories. Air infiltration is completely eliminated according to the present invention by pressurizing the door gas chamber 18 with a clean, nonoxidizing gas so that any leaks into the oven are clean, neutral gas, such as nitrogen, which is not damaging to the oven refractories. Leaks outward from the door gas chamber are clean, neutral gas and not pollutin to the atmosphere or a hazard to the workers. The systematic combination of these three elements simultaneous solves the problems associated with each and the synergy among them resul in total elimination of door emissions and the near elimination of stack emissions. SUBSTITUTESHEET

Claims: CLAIMS We claim: 1. A method for controlling fugitive door and stack emissions from a slot type coke oven comprising: a. introducing a clean, neutral or nonoxidizing gas under pressure into a gas chamber formed around the periphery of a coke oven door between a first sealing means and a second sealing means; b. allowing the coke oven gases located in the coke oven adjacent to the inside of the coke oven door to flow freely in a vertical direction within the oven adjacent to said door; and c. maintaining the collecting gas main pressure of the oven equal to or less than the pressure at the top of the heating flue within the oven. 2. The method of Claim 1 in which the pressure of the clean, neutral or nonoxidizing gas in the gas chamber is greater than said col¬ lecting gas main pressure. 3. The method of Claim 1 in which the pressure of the clean, neutral or nonoxidizing gas in the gas chamber is at least 2 mm water column greater than said collecting gas main pressure. 4. The method of Claim 1 in which a small amount of said clean, neutral or nonoxidizing gas enters the coke oven through said first sealing means. 5. The method of Claim 1 in which the pressure within the oven adjacent said door is less than 10 mm water column.

Inventors: CARPENTER JOHN A, KWASNOSKI DANIEL, CARPENTER, JOHN, A., KWASNOSKI, DANIEL
Applicants: BETHLEHEM STEEL CORP, BETHLEHEM STEEL CORPORATION
Application year: 1991
Main classification: C10B25
IPC codes: C10B25