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hey, I was wondering if I could get help for question 11-15 of this assignment. I'm a little stuck, but I've done q 1-9, thanks :)
CURTIN UNIVERSITY DEPARTMENT OF CHEMICAL ENGINEERING ChE227 PROCESS PRINCIPLES PROJECT-S1, 2012 Date Distributed: 16 April 2012 Date Due: 4:00 pm, 24 May 2012 Instructions to individual groups: Only ONE report is to be submitted by each group (3-4 students to each group) A title page including the names of partners and date of submission Declaration page where each group member with the agreement of all other members will sign against the agreed contributions to the project, ie if there is equal contribution, then each contributed 100%, otherwise the a proportion of 100% should be specified An Introduction page where the project is briefly described Document the workings and answers to the 15 questions Overall general discussion of the whole project References if any have been used Minutes of 4 meetings (1 per week) to be inserted in the appendix of the report. The minutes, maximum of 1 page each should reflect weekly discussion by the group of progress in the project. Marking Scheme: Overall presentation: 10 Minutes of group meetings: 15 5 marks per question adding to 75 as there are 15 questions Total marks is out of 100 Project Description S0 2 REMOVAL FROM POWER PLANT STACK GASES Numerous inventories of the world's energy reserves have shown that coal is the most abundant practical source of energy for the next several decades. Two immediate problems have become apparent as the use of coal has increased: mining can be costly, both economically and environmentally, and air pollutant emissions are relatively high when coal is burned. Stack gases from coal-fired furnaces contain large quantities of soot (fine unburnt carbon particles) and ash; moreover, most coals contain significant amounts of sulphur, which when burned forms sulphur dioxide, a hazardous pollutant. In this case study we examine a process to reduce pollutant emissions from coal-fired power plant boiler furnaces. Sulphur dioxide (S0 2 ) emissions from coal-fired furnaces must, by Environmental Protection Agency (EPA) regulation, contain less than 1.2 lb m ,S0 2 per 10 6 Btu (heating value of fuel fed to the boiler). When coal containing a relatively high quantity of sulfur is to be burned, the emissions standard may be satisfied by removing sulphur from the coal prior to combustion or by removing 1
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S0 2 from the product gases before they are released to the atmosphere. The technology for removing S0 2 from stack gases is currently more advanced than that for sulfur removal from coal, and a large number of stack gas desulphurisation processes are currently in various stages of commercial development. Sulphur dioxide removal processes are classified as regenerative or throwaway, according to whether or not the agent used to remove SO 2 is reusable. Regenerative processes have two major steps: the removal of S0 2 from stack gases by a separating agent, and removal of SO 2 from the separating agent. An example of such a procedure is the Wellman-Lord process-absorption of SO 2 by a solution of Na 2 S0 3 to produce NaHS0 3 , followed by the release of S0 2 by partial vaporisation of the NaHSO 3 solution. In this process the Na 2 SO 3 solution is regenerated for reuse as the absorbent. Na 2 SO 3 + SO 2 + H 2 O 2NaHSO 3 (absorption) 2NaHSO 3 Na 2 SO 3 + SO 2 + H 2 O (regeneration) Throwaway processes utilise a separating agent to remove S0 2 , followed by the disposal of both S0 2 and the separating agent. Wet limestone scrubbing is one of the most advanced throwaway processes in terms of industrial acceptance. Several versions of this process have been developed, one of which is examined in detail in this case study. BOILER-INJECTION WET LIMESTONE PROCESS DESCRIPTION The plant to be described is to produce 500 MW of electrical power. The flow rates, compositions, stream conditions, and other details to be given are representative of such installations. The key step in removing S0 2 from the stack gas is the reaction of S0 2 with Ca0 and oxygen to produce CaS0 4 , an insoluble stable compound. Four major components of the process will be traced: the coal-limestone-stack gas streams, the scrubber water, the cooling-heating water cycle, and the generated steam cycle. Coal compositions vary considerably, but generally resemble that shown in Table 1. During coal combustion the sulfur in the coal reacts to form S0 2 and very small amounts of S0 3 . Eighty- five percent of the ash in the coal leaves the boiler in the stack gas as fly ash; nitrogen emerges as N 2 , and the carbon, hydrogen and sulfur in the fuel are oxidised completely to C0 2 , H 2 0, and S0 2 . Finely ground limestone, whose composition is given in Table 2, is injected directly into the furnace where complete calcination occurs CaCO 3 CaO + C0 2 The limestone feed rate to the furnace is 10% in excess of that required for complete consumption of the generated S0 2 . Both limestone and coal enter the process at about 77 o F. A solid waste stream consisting of 15% of the limestone inerts and coal ash is removed from the 2
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