摘要:
NOx and SO3 emissions from combustion of a sulfur containing carbonaceous fuel are reduced simultaneously. The combustion gases comprising NOx and SO2 are mixed with a NOx control agent into the combustion gases at a point upstream of a selective catalytic reduction catalyst for reduction of NOx. Following an SCR catalyst or other equipment that can oxidize SO2 to SO3 and prior to contact with an air heater for heating incoming combustion air, magnesium hydroxide is introduced in amounts and with droplet sizes and concentrations effective to form nano-sized particles in the effluent and reduce SO3 caused by the oxidation of SO2 in the catalyst. Computational fluid dynamics is employed to determine flow rates and select reagent introduction rates, reagent introduction location(s), reagent concentration, reagent droplet size and/or reagent momentum.
摘要:
A preferred apparatus arrangement utilizes the enthalpy of the flue gas, which can be supplemented if need be, to convert urea (30) into ammonia for SCR. Urea (30), which decomposes at temperatures above 140 .degree. C., is injected (32) into a flue gas stream split off (28) after a heat exchanger (22), such as a primary superheater or an economizer. Ideally, the side stream would gasify the urea without need for further heating; but, when heat is required it is far less than would be needed to heat either the entire effluent (23) or the urea (30). This side stream, typically less than 3% of the flue gas, provides the required temperature and residence time for complete decomposition of urea (30). A cyclonic separator can be used to remove particulates and completely mix the reagent and flue gas. This stream can then be directed to an injection grid (37) ahead of SCR using a blower (36). The mixing with the flue gas is facilitated due to an order of magnitude higher mass of side stream compared to that injected through the AIG in a traditional ammonia-SCR process.
摘要:
A process for reducing nitrogen oxides in a combustion effluent is presented. The process involves introducing a nitrogenous treatment agent into the effluent under conditions effective to create a treated effluent having reduced nitrogen oxides concentration such that ammonia is present in the treated effluent; and then contacting the treated effluent under conditions effective to reduce the nitrogen oxides in the effluent with a nitrogen oxides reducing catalyst.
摘要:
Disclosed are methods and apparatus for providing an ammonia feed for a low-temperature process. The process includes two defined stages, gasification and hydrolysis. In a first stage thermal reactor, an aqueous urea solution is fed to a gasification chamber and heated gases are controlled in response to demand from a low temperature process requiring ammonia. The heated gases and aqueous urea are introduced into the gasification chamber upstream to fully gasify the solution of aqueous urea to a first stage gas stream comprising ammonia and isocyanic acid. The first stage gas stream is withdrawn and maintained hot enough to prevent solids formation. All amounts of urea feed, water and heated gases fed into the first stage thermal reactor are monitored and adjusted as necessary to achieve efficient hydrolysis in the second stage hydrolysis reactor. The second stage gas stream is withdrawn from the second stage reactor responsive to demand from a low temperature process requiring ammonia.
摘要:
Disclosed is a system which enables the efficient utilization of urea for selective catalytic reduction (SCR) of NOx by gasifying it and feeding it to a plurality of selective catalytic reduction units associated with a plurality of gas turbines. The invention enables feeding a gasified product of the urea with the ability to fully control separate SCR units without excessive reagent usage or loss of pollution control effectiveness. Controllers determine the amount of reagent required for each turbine to control NOx emissions and then mixes the gasified urea with the correct amount of carrier gas for efficient operation of each separate SCR unit despite the demand variation between the turbines. In this manner the gasification unit can be properly controlled to provide urea on demand without the need for storing large inventories of ammonia-containing gasses to correct for fluctuations in demand.
摘要:
Nitrogen oxides are reduced in gas turbines by selective, gas-phase reaction with urea. This is enabled in a preferred embodiment by injecting urea as an aqueous solution of droplet sizes and concentration effective to assure selective gas phase reactions to result in NO.sub.x reduction. The aqueous solution can also be employed to reduce NO.sub.x by reducing the flame temperature. Desirably, the injection parameters are controlled to also minimize ammonia production.
摘要:
A process and apparatus is presented for the reduction of nitrous oxide in the effluent from the combustion of a carbonaceous fuel. The process comprises raising the temperature of the effluent to a temperature of at least about 1700.degree. F. The apparatus utilized is a heating means which is disposed in a boiler at a location where the effluent is at a temperature of less than about 1700.degree. F.
摘要:
Disclosed is a system which enables the efficient utilization of urea for selective catalytic reduction (SCR) of NOx by gasifying it and feeding it to a plurality of selective catalytic reduction units associated with a plurality of gas turbines. The invention enables feeding a gasified product of the urea with the ability to fully control separate SCR units without excessive reagent usage or loss of pollution control effectiveness. Controllers determine the amount of reagent required for each turbine to control NOx emissions and then mixes the gasified urea with the correct amount of carrier gas for efficient operation of each separate SCR unit despite the demand variation between the turbines. In this manner the gasification unit can be properly controlled to provide urea on demand without the need for storing large inventories of ammonia-containing gasses to correct for fluctuations in demand.
摘要:
Disclosed are methods and apparatus for providing an ammonia feed for a low-temperature process. The process includes two defined stages, gasification and hydrolysis. In a first stage thermal reactor, an aqueous urea solution is fed to a gasification chamber and heated gases are controlled in response to demand from a low temperature process requiring ammonia. The heated gases and aqueous urea are introduced into the gasification chamber upstream to fully gasify the solution of aqueous urea to a first stage gas stream comprising ammonia and isocyanic acid. The first stage gas stream is withdrawn and maintained hot enough to prevent solids formation. All amounts of urea feed, water and heated gases fed into the first stage thermal reactor are monitored and adjusted as necessary to achieve efficient hydrolysis in the second stage hydrolysis reactor. The second stage gas stream is withdrawn from the second stage reactor responsive to demand from a low temperature process requiring ammonia.
摘要:
A process and an apparatus enhance urea utilization for selective catalytic reduction (SCR) of NOx, by controlled preparation and feed of gasified urea during combustor load variation. The concentration of NOx in the combustion gases and a required total gas flow necessary to supply an SCR reactor with NOx reducing and carrier gases are determined. Urea is gasified by gasification gases in a thermal gasification reactor. The resulting urea gasification products are mixed with carrier gases to provide an injection grid supply stream. Heating is reduced and flue gas enthalpy is efficiently used by controls utilizing monitoring the temperatures of gases fed to the thermal gasification reactor and of the stream of carrier gases.