Fuel Tech, Inc.

Paul G Carmignani

William H Sun

John M Boyle

Scott M Mayhew

William E Cummings, Jr

Piers De Havilland

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 The first stage gas stream is withdrawn and maintained hot enough to prevent solids formation.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 The second stage gas stream is withdrawn from the second stage reactor responsive to demand from a low temperature process requiring ammonia.

Ammonia gas generation from urea for low temperature process requirements

Disclosed are methods and apparatus for treating and analyzing a gas stream to determine the ammonia concentration. A gas stream is continuously monitored to determine the ammonia concentration by extracting gas samples from one or more locations and sending it to a tunable diode laser absorption spectroscopy instrument for analysis. By proper placement of sampling probes within a duct, depending on the particular flow patterns that have been determined by suitable modeling, e.g., computational fluid dynamics or cold flow modeling, the valves can be operated manually or by a controller to take samples at predetermined locations within the duct. This will enable taking samples from particular locations, samples representative of the entire cross section, or samples that are an average of a particular cross section. It will be possible by judicious placement of the probes and operation of the valves to map the concentrations of ammonia at a plurality of load settings and will permit continuous control.

Extractive continuous ammonia monitoring system

Disclosed is a system which enables the efficient utilization of urea for selective catalytic reduction (SCR) of NOby 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 NOemissions 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.

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A process and an apparatus enhance urea utilization for selective catalytic reduction (SCR) of NO, by controlled preparation and feed of gasified urea during combustor load variation. The concentration of NOin the combustion gases and a required total gas flow necessary to supply an SCR reactor with NOreducing 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.

A preferred apparatus arrangement utilizes the enthalpy of the flue gas, which can be supplemented if need be, to convert urea () into ammonia for SCR. Urea (), which decomposes at temperatures above 140 .degree. C., is injected () into a flue gas stream split off () after a heat exchanger (), 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 () or the urea (). This side stream, typically less than 3% of the flue gas, provides the required temperature and residence time for complete decomposition of urea (). 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 () ahead of SCR using a blower (). 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.

A preferred process arrangement utilizes the enthalpy of the flue gas, which can be supplemented if need be, to convert urea () into ammonia for SCR. Urea (), which decomposes at temperatures above 140 &#xb0; C., is injected () into a flue gas stream split off () after a heat exchanger (), 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 () or the urea (). This side stream, typically less than 3% of the flue gas, provides the required temperature and residence time for complete decomposition of urea (). 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 () ahead of SCR using a blower (). 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.

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Naperville, IL, United States of America

Paul G Carmignani