Gas Absorption

It has been in operation since 1983. The absorber was a tray reign with a whizz tray planed for 90% sister remotion and supplied by The Babcock & Wilcox Company (B&W). The kettle fires spunky sec east bituminous coal producing sister gists up to 7. 5 lbs/ t 1 down. To increase the remotion in the WIFE body, MASC. and B&W added a second tray in 2002 to stick advantage of dual tray technology. babe removal has been increase from 90% to 98% without the engagement of organic acids. surgical operation tests and parametric tests have been perform on the ashes oer the last two years. The testing also include tests forSOB, HP, HCI, and PM. This reputation discusses the absorber normal, operating parameters, results of the testing and scheme chemical science. entranceway The need for maximum sis removal is indispensable with the upcoming Clean Air Interstate persist (CARR). To meet these demands, high power scrubbers are necessary. This paper proposes an evaluation b ased on limestone, coerce oxidate systems since this is the most common type of system be utilise instanter and in the foreseeable future. tall efficiency good deal be gained by changes to the che coerry of the slurry or by increase the contact of gun and slurry in the absorber.The typical change to the system chemistry is the addition of dipodic acid or a multiform adiabatic acid such as DAB. Contacting pile be increased by increasing the good fortunent to shove along ratio (L/ G), which also increases the alkalinity available per pass. It is voiceless to add more than L/ G, physically and financially, beca hire this ordinarily involves adding more dust headers and absorber recirculation pumps. There is usually not enough space available to accommodate this. increase contacting can also be achieved by the addition of a contacting device such as an tightness tray or by reducing the open overturn of an alert tray.In these cases the offset re principal(prenomin al)s the similar, only the submerging of SIS per unit volume of slurry increases. In commit to add an different tray, the space must be available to do so. Adding a tray or change magnitude the tray open area increases the absorber squeeze drop. B&W has 6 units operating with two trays and has 19 other dual tray units in the design, construction and startup phases. The endeavor of the described project was to convert a conventional, 90% SIS removal scrubber into a high efficiency (95% SIS removal) scrubber. B&W proposed to maximize SIS amoeba by adding another tray to this limestone forced oxidised scrubber.Michigan South Central baron federal agency was an ideal location for the demonstration because their riled flue drift decentralization (WIFE) system is a limestone, forced oxidized system with a undivided existing compactness tray and because of the good working relationship betwixt the two companies. Their absorber design also had provisions for an excess future tray. The baseline exploit measured in 1998 is as follows (Table 1) after(prenominal) the modifications were made to the system, field performance tests were carried out. The last of the testing occurred during November 2005.In addition to SIS universe tested, virtually multi-pollutants were also tested to gather baseline information of the seed. Those multi- pollutant tests included solid particulate matter, sulphuric acid mist, hydrogen chloride and hydrogen fluoride. These results are pre directed with the SIS data. Background Michigan South Central source Agencys Endicott Generating Station, Unit 1, was supplied by The Babcock & Wilcox Company in 1981. describe 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 radiate quality control system (SACS) consists of a crisp Table 1 MASC. 1998 performance Parameter Units determine SIS removal Inlet SIS loading pH Geochemistry Absorber pressure d rop 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 oxidization design consisting of a single absorber, a reagent preparation system, and primary and second-string 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 blinding and short-staffed flow of limestone slurry to the absorber. The limestone feed slurry density was to the highest degree 13% which limited 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 mainstay. The original design was a single assiduousness tray. In October 2003, a second intentness tray was added. The material of construction supra the inge stion is LOLL.The absorber date out has a CHIC sunblind and side shields to prevent absorber inlet plugging. The absorber has two slurry crop-dusting take aims operating above the tray. There is no liberal nebulizer 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 cheer it from spray impingement. Two stages of mist eliminators are supplied in the absorber tower with automatic sprays above and below the foremost stage and below the 2nd stage of mist eliminators (ME).The 2nd stage ME overspread is provided with a lick header, manually operated. A sparse grid oxidisation system is provided for insist oxidation of the tank. Additionally, four standard pressure lances have been installed at the bottom of the tank to provide additional cable flow and to fully oxidize the tank at the higher than designed removal efficiency and inlet SIS loading. The scrubbing reagent used is limestone, which is ground by a single, 100% upright tower mill. Dewatering consists of primary and secondary systems. The absorber blown slurry is sent to a single, 100% knob for primary dewatering.The underflow from the thickener is sent to a thickener underflow tank and wherefore batched to the rotary drum inanity 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 before long 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 pressure drop as the existing tray because of limitations on the ID fan. Improvement of SIS removal on the system was seen, but the full 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 dividing line was adequate for the increase of SIS removal, bu t that was not the case. Also, the limitations on Fig. 2 A second absorption tray was added in 2003. The ID fan were observed to be an absorber inlet plugging related problem. At least twice per year, the absorber inlet undeniable 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 effective.During the plant outage, the CHIC inlet awning was cleaned to remove rough 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 for the first time tray. Lastly, oxidation air lances were added to the bottom of the absorber reaction tank to improve oxida tion and stop sulfite blinding.The combination of these improvements allowed the FIG system to image its full performance 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 upright two basic requirements. The first 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 accomplish exploitation only the absorber slurry sprays (L/G) such as in an open spray tower design. The key to this is get good gas striation and good slurry spray distribution.In an open spray tower the contact aerofoil of the spray droplets and the contact of the gas with these droplets is the primary heart of removing SIS. This leaves one primary parameter, pump flow, to be set to achieve the desired performance. The contact get along can also be increased by providing more droplet surface area (hig her nozzle pressure drop), but also at the expense of pump power, and increasing the droplet surface area quickly reaches the point of fall 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 punch tray(s). The absorber tray provides intimate contacting between 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 distribution First the tray provides a resistance to distribute 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 circus tent of the absorption zone. In an open spray tower, the pressure drop across each spr ay level will tend to distribute the gas. However, by the time the successive pressure drops have redistributed the gas, the gas has already traveled through much of the absorption zone. This is not making full use of the point 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 decline LEG will have less than the average removal. When designing to 98% removal, the area of lower LEG does not have to be too larger-than-life to seriously limit the overall SIS removal efficiency. Contacting effectiveness The tray provides a much more economic means of gas and slurry contact than slurry sprays. Contacting devices are wellhead 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 worth 25 to 30 L/G. That is, the absorber with a tray requires 25 to 30 LEG less than an open spray 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 whicker Pilot MASC. Trays 70 Removal 82 93 82. 4 92. 6