Gas Absorption

It has been in operation since 1983. The absorber was a tray tower with a single tray determinati wizardd for 90% babe removal and supplied by The Babcock & Wilcox Company (B&W). The boiler fires utmost sulfur eastern bituminous coal producing baby loadings up to 7. 5 lbs/ benumb. To increase the removal in the WIFE dodging, MASC. and B&W added a second tray in 2002 to take advantage of triple tray technology. SIS removal has been increased from 90% to 98% without the use of organic acids. Performance tests and parametric tests pay off been perform on the organization over the last both years. The test likewise included tests forSOB, HP, HCI, and PM. This paper discusses the absorber bearing, operate parameters, results of the testing and system interpersonal chemistry. presentment The need for maximum SIS removal is necessary with the upcoming light-headed Air Interstate Rule (CARR). To meet these demands, highschool cogency scrubbing brushs are necessary. This pa per provides an evaluation based on limestone, forced oxidized systems since this is the most common slip of system cosmos used now and in the foreseeable future. High efficiency can be gained by changes to the chemistry of the slurry or by increasing the abut of spoil and slurry in the absorber.The classifiable change to the system chemistry is the addition of dipodic acid or a composite adiabatic acid such as DAB. Contacting can be increased by increasing the liquid to flatulency ratio (L/ G), which in addition increases the alkalinity available per pass. It is difficult to add more L/ G, physically and financially, because this usually involves adding more spraying headers and absorber recirculation pumps. There is usually non enough pose available to accommodate this. Increased contacting can also be achieved by the addition of a contacting device such as an absorption tray or by reducing the open rear of an existing tray.In these cases the offshoot body the same, but the absorption of SIS per building block volume of slurry increases. In invest to add another tray, the space must be available to do so. Adding a tray or decreasing the tray open area increases the absorber compress pin. B&W has 6 units operating with two trays and has 19 other dual tray units in the design, construction and startup phases. The purpose of the described project was to diversify a conventional, 90% SIS removal scrubber into a high efficiency (95% SIS removal) scrubber. B&W proposed to maximize SIS ameba by adding another tray to this limestone forced oxidized scrubber.Michigan South Central motive Agency was an ideal location for the demonstration because their wet flue bodge decentralization (WIFE) system is a limestone, forced oxidized system with a single existing absorption tray and because of the good working relationship amidst the two companies. Their absorber design also had provisions for an additional future tray. The service line performance measured in 1998 is as follows (Table 1) After the modifications were made to the system, theater of operations performance tests were carried out. The last of the testing occurred during November 2005.In addition to SIS being tested, whatever multi-pollutants were also tested to gather baseline data of the workings. Those multi- pollutant tests included substantialness particulate matter, sulfuric acid mist, hydrogen chloride and hydrogen fluoride. These results are presented with the SIS data. Back object Michigan South Central Power Agencys Endicott Generating Station, Unit 1, was supplied by The Babcock & Wilcox Company in 1981. See Fig. 1. The boiler is a Sterling design rated for 480,000 lb/hrs steam flow and a nominal 55 MM while burning bituminous coal.The vent quality control system (SACS) consists of a cold Table 1 MASC. 1998 performance Parameter Units value SIS removal Inlet SIS loading pH Geochemistry Absorber insistency swing over lb/Numb -ca/S CPM/masc. in. Wag 6. 5 5. 6 1. 06 85 3. 6 electrostatic precipitated (ESP.) and wet FIG. The FIG system is a forced oxidation design consisting of a single absorber, a reagent set system, and primary and vicarious dewatering systems. Prior to adding the new, second tray, the scrubber performance had deteriorated and the plant struggled to meet compliance t high sulfur loadings, 6. Lb/Numb and high boiler loads, 60 MM. The primary reasons for this poor performance were sulfite gross and in satisfactory flow of limestone slurry to the absorber. The limestone feed slurry density was about 13% which restrict the limestone flow. The pH was limited to 4. 6 to 4. 8. SIS removal totald about 83% with a single tray. The absorber system consists of one 226 diameter absorber tray tower. The original design was a single absorption tray. In October 2003, a second absorption tray was added. The material of construction above the doorway is LOLL.The absorber door has a fashionable sunblind and side shiel ds to prevent absorber inlet plugging. The absorber has two slurry spray levels operating above the tray. There is no spare spray level. Three absorber recirculation pumps, two operating and one standby, are provided to feed the slurry spray headers. The absorption spray zone is lined with Stabbing tile to protect it from spray impingement. dickens stages of mist eliminators are supplied in the absorber tower with automatic sprays above and at a lower place the 1st stage and below the second stage of mist eliminators (ME).The 2nd stage ME overspread is provided with a wash header, manually operated. A slight grid oxidation system is provided for insist oxidation of the tank. Additionally, four walkover lances have been installed at the bottom of the tank to provide additional air flow and to aboundingy oxidize the tank at the higher than knowing removal efficiency and inlet SIS loading. The scrubbing reagent used is limestone, which is ground by a single, 100% vertical tower mill. Dewatering consists of primary and secondary systems. The absorber blown slurry is sent to a single, 100% thickening for primary dewatering.The underflow from the thickener is sent to a thickener underflow tank and then batched to the rotary vex vacuum filters. Two vacuum filters are provided, one operating and one spare. A gypsum byproduct is produced from the cake of the vacuum filter and is currently being landfill. In 2003, a second absorption tray was added to the absorber tower. See Fig. 2. This new tray did not have the same mash drop as the existing tray because of limitations on the ID fan. Improvement of SIS removal on the system was seen, but the amply effect was not observed. The removal increased from 83% to bout 89%.The main reason was continued sulfite blinding. It was expected that the delivered oxidation air was adequate for the increase of SIS removal, but that was not the case. Also, the limitations on Fig. 2 A second absorption tray was added in 2003. T he ID fan were observed to be an absorber inlet plugging related problem. At least twice per year, the absorber inlet needed to be cleaned before upsetting boiler operations because of high differential pressure drop. In 2005, a few more modifications were made to the system for system reliability and to enable the second tray to be more utile.During the plant outage, the chic inlet awning was cleaned to remove somewhat hard solids, which developed over the years, at the top gap in the awning. After cleaning, it was discovered that the awning was severely corroded and needed replaced. This new awning resolved the inlet plugging issues. Next, some rubber plugs were added to the second absorption tray to increase the pressure drop so that it equaled the starting line tray. Lastly, oxidation air lances were added to the bottom of the absorber reaction tank to improve oxidation and stop sulfite blinding.The combination of these improvements allowed the FIG system to fade its full p erformance capacity. SIS removals can now reach as high as 98%. SIS absorption theory scrubber design and SIS absorption The design of a wet scrubber can be reduced to Just two basic requirements. The showtime is to contact the gas and slurry. The second is to provide alkalinity to neutralize the acid formed when SIS is absorbed. Contacting the gas and slurry can be accomplished using plainly the absorber slurry sprays (L/G) such as in an open spray tower design. The find out to this is getting good gas striation and good slurry spray dispersal.In an open spray tower the contact prove of the spray droplets and the contact of the gas with these droplets is the primary doer of removing SIS. This leaves one primary parameter, pump flow, to be set to achieve the desired performance. The contact surface can also be increased by providing more droplet surface area (higher nozzle pressure drop), but also at the expense of pump power, and increasing the droplet surface area quickly reaches the point of diminishing returns. The gas and slurry contacting and SIS amoeba can be greatly improved by using some type of contacting device(s).B&Ws choice of contacting device is a perforated tray(s). The absorber tray provides intimate contacting in the midst of the gas and slurry. The contact surface provided by the tray is much more effective for SIS removal than that of the slurry droplets in a spray tower design. Fig. 1 Michigan South Central Power Agencys Endicott Station. 2 Gas dispersal First the tray provides a resistance to progress the gas flow uniformly over the tower cross-section. This resistance is provided at the start of the gas and slurry contact one, or the absorption zone, in the absorber.Therefore, the contact of the gas with slurry is optimized over the full height of the absorption zone. In an open spray tower, the pressure drop across each spray level will tend to distribute the gas. However, by the time the successive pressure drops have redist ributed the gas, the gas has already traveled through much of the absorption zone. This is not make full use of the offset being provided. Uneven gas distribution results in areas of high and low LEG within the absorber. In areas where the LEG is higher than the design L/G, theSIS removal will be higher than design. However, areas of lower LEG will have less than the average removal. When designing to 98% removal, the area of lower LEG does not have to be too large to seriously limit the overall SIS removal efficiency. Contacting effectiveness The tray provides a much more efficient means of gas and slurry contact than slurry sprays. Contacting devices are well known to provide the optimum design in most gas-liquid absorption systems. In fact, most of the first utility scrubber designs were based on the use of some type of packing or trays.The use of a tray in an absorber is typically outlay 25 to 30 L/G. That is, the absorber with a tray requires 25 to 30 LEG less than an open s pray tower design. This is illustrated in field unit test data presented in Fig. 3. The curves indicate that 80% removal efficiency could be achieved operating without a tray at 60 LEG or with a tray at about 35 L/G. The data also indicates 95% removal at 60 LEG and using a single absorption tray. Fig. 3 SIS removal with and without tray. Table 2 Effect of Trays on SO 2 Removal Unit emit Pilot MASC. Trays 70 Removal 82 93 82. 4 92. 6