Fuel Tech, Inc.

Nalco Fuel Tech

William H Sun

John M Boyle

John E Hofmann

Paul G Carmignani

M Linda Lin

Christopher R Smyrniotis

William F Michels

Scott M Mayhew

Daniel V Diep

Ronald A Lau

Piers De Havilland

Penelope Stamatakis

Bryan K Luftglass

M Damian Marshall

Cari M Chenanda

William E Cummings, Jr

Barry N Sprague

Kent W Schulz

Vasudeo S Gavaskar

Scott Bohlen

J David Martin

David M Kieffer

Fabian Johan Solberg

Christopher R Symrniotis

Gerry Carl Snow

Steven William Cottingham

Glenn Brewer

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 is a process for controlling injection of magnesium oxide (or precursor) for reducing the concentration of sulfur trioxide in combustion gases from a combustor burning vanadium and sulfur-containing fuel while operating the boiler with enhanced efficiency. In-fuel introduction is combined with mid-temperature introduction, where both can be operated effectively, are found to be of primary importance. When in-fuel introduction will not be effective due to selectivity problems, feed can be shifted to a high-temperature zone. Where the high- or mid-temperature zone cannot be fully utilized due to obstructions for injection or insufficient soot blowers to address fouling of that zone or boiler operational changes to integrate the magnesium oxide injection is insufficient, an entire or a portion of feed can be shifted to the low-temperature zones.

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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.

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 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 slag and corrosion control process is described. The process entails: identifying the location of at least one slagging problem area in a boiler; introducing a slag control chemical comprising magnesium oxide or hydroxide into combustion gases in a location identified as having a slagging problem; identifying the location of at least one corrosion problem area in a boiler; and introducing a corrosion control chemical comprising a sulfate salt, bisulfite salt, sulfuric acid, or sulfur into combustion gases in a location identified as having a corrosion problem. In operation, these slag deposits will be sufficiently friable to be removed by relatively moderate application of physical energy, thus saving time and reducing any damage to the tubes by the cleaning process. The slag deposits are less voluminous and less in weight and are removed quickly. It is an advantage of the invention that slag can be removed with little or no shut down of a boiler.

Process for slag and corrosion control in boilers

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.

NOand SOemissions from combustion of a sulfur containing carbonaceous fuel are reduced simultaneously. The combustion gases comprising NOand SOare mixed with a NOcontrol agent into the combustion gases at a point upstream of a selective catalytic reduction catalyst for reduction of NO. Following an SCR catalyst or other equipment that can oxidize SOto SOand 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 SOcaused by the oxidation of SOin 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.

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.

Selective catalytic reduction of nox enabled by sidestream urea decomposition

Reduction of slagging is improved by targeting slag-reducing chemicals in a furnace with the aid of computational fluid dynamic modeling. Chemical utilization and boiler maintenance are improved.

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Lisle, IL, United States of America

William H Sun