Fuel Tech, Inc.

John M Boyle

William H Sun

Paul G Carmignani

Scott M Mayhew

M Linda Lin

Ronald A Lau

Penelope Stamatakis

William E Cummings, Jr

Piers De Havilland

David M Kieffer

Disclosed are methods and compact apparatus for controlled, on-demand ammonia generation from urea. The process gasifies an aqueous urea solution in a chamber utilizing hot gas while controlling the flows of aqueous urea solution and hot gas to achieve complete gasification of the aqueous urea solution and form a gas mixture comprising ammonia, isocyanic acid, carbon dioxide and water vapor, which is passed through a catalyst bed containing particulate transition metal oxide to convert substantially all of the isocyanic acid to ammonia. A catalyst support and the catalyst bed are aligned with the gasification chamber at the lower end of said chamber to provide a degree of back pressure on the gases in the gasification chamber to isolate the gasification chamber from turbulent exit effects caused by equipment downstream of the thermal reactor. A sample of the product stream is treated to remove water and ammonia, and analyze for carbon dioxide content to control the process. The apparatus to perform the process includes flow managing equipment and catalyst supports that facilitate continuous operation with accurate control.

Controlled, compact, on-demand ammonia gas generation process and apparatus

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 The first stage gas stream is withdrawn and maintained hot enough to prevent solids formation.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 The second stage gas stream is withdrawn from the second stage reactor responsive to demand from a low temperature process requiring ammonia.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 effectiveness of urea gasification. The apparatus will be capable of performing the method and will include: means for introducing an aqueous solution of urea into a reactor having hot gases therein and subjecting the aqueous to temperatures for a time to assure the gasification of the aqueous urea and form a thermal gasification product stream containing NHand HNCO; means for taking a sample stream from the gasification product stream; means for contacting the sample stream with a hydrolysis catalyst in the presence of sufficient water to convert HNCO to NHand form an ammonia sample stream; and means for analyzing the ammonia sample stream for NH. The methods and apparatus can also be used to control a urea gasification process and/or to signal anomalous operation.

Diagnostic tool and process for assessing thermal urea gasification performance

Disclosed are methods and apparatus enabling the efficient utilization of urea for purposes such as selective catalytic reduction (SCR) of NO, which enable feeding urea to a chamber designed to efficiently and completely gasify the urea to enable ammonia feed. Preferably, aqueous urea is fed to a gasification chamber, which is also fed with heated gases. An injector means, capable of distributing the aqueous urea as fine droplets, is positioned centrally of a gas distribution plate in the chamber. An arrangement of spaced holes in the gas distribution plate provides higher gas velocity in the vicinity of the injector means than near the walls of the chamber. Uniform gas distribution without equipment fouling is achieved.

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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.

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.

Disclosed are a process and apparatus for selective catalytic reduction of NO. The process is enabled by bypassing a heat exchanger section, such as an economizer, of the boiler in advance of an SCR unit at low load conditions to enable NOreduction even at low loads using urea instead of ammonia. In a preferred form, under high load conditions, the bypass can be almost fully closed and the economizer can be operated normally without excessively cooling the combustion gases, using only a portion of bypassed gases which are hot enough to decompose the urea into its active components including ammonia.

Disclosed are a process and apparatus for selective catalytic reduction of NO. The process is enabled by passing a heat exchanger section, such as an economizer, of the boiler in advance of an SCR unit at low load conditions to enable NOreduction even at low loads using urea instead of ammonia. In a preferred form, under high load conditions, the bypass can be almost fully closed and the economizer can be operated normally without excessively cooling the combustion gases, using only a portion of bypassed gases which are hot enough to decompose the urea into its active components including ammonia.

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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Oak Park, IL, United States of America

John M Boyle