FIELD OF THE INVENTION

The present invention relates, generally, to the field of NOxreduction. More particularly, the present invention relates to SCR for NOxreduction in boilers and other fired vessels.

BACKGROUND OF THE INVENTION

The ever-increasing emissions from combustion sources have led to increasing efforts to reduce fugitive emissions from these sources. Existing measures for NOx(nitrogen oxides) reduction in boilers include two-stage combustion, exhaust gas recirculation, rapid mix burners, high excess air with air/fuel pre-mixed and the like. In two-stage combustion, combustion air is supplied in two stages to the burner, where the fuel is burned with a smaller amount of air than necessary for complete combustion in the first stage, and the remaining amount of air necessary for complete combustion is supplied in the second stage, thereby lowering peak combustion temperatures and reducing NOxformation. In exhaust gas recirculation, exhaust gas generated by combustion is re-circulated so as to be mixed with the combustion air and fed to the burner, thereby also lowering peak combustion temperatures and reducing NOxformation. Rapid mix burners employ both exhaust gas recirculation (e.g., flue gas recirculation) and a rapid mix of fuel and air in the burner. The rapid mix promotes air/fuel distribution in the flame which reduces localized high temperatures in the flame which reduces NOxformation. Pre-mix burners mix fuel and air just prior to combustion to provide uniform air/fuel mixtures combined with high excess air to reduce NOxformation.

While these known methods have been effective at reducing NOxformation, the reduction has come at the cost of at least some reduction in boiler performance. For example, in at least some respects, boilers employing the above methods show a diminished response to load changes, an increase in the horsepower necessary for the combustion air fan motor to move the additional volumes of air, and an increase in operating costs due to an increased electrical energy demand.

Selective catalytic reduction (SCR), using post-combustion oxidation catalysts to reduce NOx, has been an effective means for reducing NOxemissions without sacrificing boiler performance. In SCR, an ammonia source is required for the oxidation catalyst to remove NOxfrom the boiler flue gases. Anhydrous ammonia is the most readily usable source of ammonia in SCR applications. However, anhydrous ammonia poses significant safety hazards if the boiler system leaks or fails. Anhydrous ammonia has a health hazard rating of 3 on a scale of 0 to 4, with even short exposure capable of causing serious temporary or residual injury, even if prompt medical care is given. Eye wash stations, ambient ammonia sensors, and alarms are required to manage the health hazards of anhydrous ammonia. Moreover, many boiler installations are in hospitals, schools, prisons and universities where a large, and sometimes already susceptible or weak, population could be exposed to anhydrous ammonia during a leak or failure. This could be catastrophic.

Some boilers now employ aqueous methods of ammonia or reducing urea to ammonia to avoid some of the health risks associated with storing large amounts of anhydrous ammonia. Urea is particularly attractive to use in Noxreduction systems as urea has a health hazard rating of 1 on a scale of 0 to 4, with short exposure potentially causing irritation but only minor residual injury even if no treatment is given. Boilers which incorporate methods of reducing urea to ammonia typically employ additional external heat sources and methods to convert urea to ammonia external to the boiler or through various ducts and side streams of flue gas before adding dilution air to the ammonia for delivery through an ammonia injection grid located upstream from the catalyst bed.

Delivering the oxidizing agent in these systems to the flue gas requires external ducting with heat tracing, insulation, hot gas fans, and other components. Failure of the heat tracing or insulation systems results in fouling of the delivery system causing unscheduled shut-down and maintenance. Moreover, these systems and added components increase the complexity and cost of boiler systems, increase the average maintenance costs of the boiler, and consume a larger amount of energy to deliver the oxidizing agent to the flue gas stream.

For at least these reasons, therefore, it would be advantageous if a new or improved method for SCR NOxreduction could be developed that addressed one or more of the above-described concerns, and/or other concerns. Particularly, it would be advantageous if a new or improved method for SCR NOxreduction could be provided for the low emission demands of the regulatory environment and the efficiency and performance demands for reduced energy costs, and without sacrificing safety.

SUMMARY OF THE INVENTION

In accordance with one embodiment, disclosed herein is a boiler or other fired vessel assembly.

In accordance with one embodiment, disclosed herein is a boiler or other fired vessel assembly comprising a housing comprising a burner at a first end, a furnace downstream of the burner, a convection section downstream of the furnace, and a flue gas outlet downstream of the convection section; a first means for loading a reducing agent into the housing, wherein the first means for loading the reducing agent is located downstream of the furnace and comprises at least two injectors; a second means for loading a reducing agent into the housing, wherein the second means for loading the reducing agent is located downstream of the first means for loading the reducing agent and comprises at least one injector; and a selective catalytic reduction (SCR) catalyst located either downstream of the second means for loading a reducing agent into the housing or adjacent the second means for loading a reducing agent into the housing such that the SCR catalyst is provided to the boiler approximately simultaneously with the reducing agent from the second means for loading the reducing agent into the housing.

In accordance with a further embodiment, disclosed herein is a boiler or other fired vessel assembly comprising a housing comprising a burner, an intermediate furnace, a convection section downstream from the intermediate furnace, and a flue gas outlet downstream of the convection section; a first means for loading a reducing agent into the housing, wherein the first means for loading the reducing agent is located downstream of the furnace and comprises at least two injectors; a second means for loading a reducing agent into the housing, wherein the second means for loading the reducing agent is located downstream of the first means for loading the reducing agent and comprises at least one injector; and a selective catalytic reduction (SCR) catalyst located either downstream of the second means for loading a reducing agent into the housing or adjacent the second means for loading a reducing agent into the housing such that the SCR catalyst is provided to the boiler approximately simultaneously with the reducing agent from the second means for loading the reducing agent into the housing.

In accordance with a further embodiment, disclosed herein is a method of reducing NOxin a boiler or other fired vessel which produces a direct flame.

In accordance with a further embodiment, disclosed herein is a method of reducing NOxin a boiler or other fired vessel which produces a direct flame, the method comprising providing (a) a first amount of a reducing agent to the boiler or other fired vessel at a first location downstream of the direct flame when a temperature of the first location is greater than or equal to a threshold temperature, or (b) a second amount of reducing agent to the boiler or other fired vessel at a second location downstream of the direct flame when a temperature of the first location is less than the threshold temperature, wherein the first location is downstream of the second location; and providing a selective catalytic reduction catalyst either downstream of or at generally the same location as second amount of a reducing agent, wherein the second amount of reducing agent is provided using at least two injectors.

In accordance with a further embodiment, disclosed herein is a method of retrofitting a boiler or other fired vessel the boiler or other fired vessel comprising a housing with a burner, an intermediate furnace, a convection section downstream of the furnace, and a flue gas outlet downstream of the convection section, with a NOxremoval system.

In accordance with a further embodiment, disclosed herein is a method of retrofitting a boiler or other fired vessel, the boiler or other fired vessel comprising a housing with a burner, an intermediate furnace, a convection section downstream of the furnace, and a flue gas outlet downstream of the convection section, with a NOxremoval system, the method comprising determining one or more parameters of the boiler or other fired vessel, wherein at least one of the one or more parameters is selected from the group consisting of internal shape of the boiler or other fired vessel, internal shape of the furnace, internal shape of the convection section, internal shape of the flue gas outlet, peak temperature of the furnace, peak temperature of the convection section, peak temperature of the flue gas outlet, operable temperature range of the furnace, operable temperature range of the convection section, operable temperature range of the flue gas outlet, concentration range of NOxformation, operable firing range, type of NOxcompounds and concentration range of one or more types of NOxcompounds, operating conditions causing peak NOxformation and combinations thereof; determining one or more parameters of a NOxremoval system, wherein at least one of the one or more parameters is selected from the group consisting of SCR catalyst to be used, reducing agent to be used, number of reducing agent loading points, locations of reducing agent loading points, type of means for loading reducing agent, timing of reducing agent loading at each reducing agent loading point, concentration of reducing agent loading at each reducing agent loading point, spray pattern of the means for loading reducing agent at each reducing agent loading point, dilution or dilution range of the reducing agent, and combinations thereof; providing, based on the one or more parameters of the NOxremoval system, a first means in communication with the housing for providing a reducing agent into the housing of the boiler or other fired vessel downstream of the furnace, wherein the first means comprises at least two injectors; providing, based on the one or more parameters of the NOxremoval system, a second means in communication with the housing for providing a reducing agent into the housing of the boiler or other fired vessel downstream of the first means for providing reducing agent; and providing, based on the one or more parameters of the NOxremoval system, a selective catalytic reduction catalyst downstream from or simultaneously with the second means for providing a reducing agent.

In accordance with a further embodiment, disclosed herein is a boiler assembly.

In accordance with a further embodiment, disclosed herein is a boiler assembly comprising a housing comprising a burner at a first end, a furnace downstream of the burner, a convection section downstream of the furnace, and a flue gas outlet downstream of the convection section; a first means for loading a reducing agent into the housing, wherein the first means for loading the reducing agent is located downstream of the furnace and comprises at least two injectors; a second means for loading a reducing agent into the housing, wherein the second means for loading the reducing agent is located downstream of the first means for loading the reducing agent and comprises at least one injector; and a selective catalytic reduction (SCR) catalyst located either downstream of the second means for loading a reducing agent into the housing or adjacent the second means for loading a reducing agent into the housing such that the SCR catalyst is provided to the boiler approximately simultaneously with the reducing agent from the second means for loading the reducing agent into the housing.

In accordance with a further embodiment, disclose herein is a boiler assembly comprising a housing comprising a burner, an intermediate furnace, a convection section downstream from the intermediate furnace, and a flue gas outlet downstream of the convection section; a first means for loading a reducing agent into the housing, wherein the first means for loading the reducing agent is located downstream of the furnace and comprises at least two injectors; a second means for loading a reducing agent into the housing, wherein the second means for loading the reducing agent is located downstream of the first means for loading the reducing agent and comprises at least one injector; and a selective catalytic reduction (SCR) catalyst located either downstream of the second means for loading a reducing agent into the housing or adjacent the second means for loading a reducing agent into the housing such that the SCR catalyst is provided to the boiler approximately simultaneously with the reducing agent from the second means for loading the reducing agent into the housing.

In accordance with a further embodiment, disclosed herein is a method of reducing NOxin a boiler which produces a direct flame.

In accordance with a further embodiment, disclosed herein is a method of reducing NOxin a boiler which produces a direct flame, the method comprising providing (a) a first amount of a reducing agent to the boiler at a first location downstream of the direct flame when a temperature of the first location is greater than or equal to a threshold temperature, or (b) a second amount of reducing agent to the boiler at a second location downstream of the direct flame when a temperature of the first location is less than the threshold temperature, wherein the first location is downstream of the second location; and providing a selective catalytic reduction catalyst either downstream of or at generally the same location as second amount of a reducing agent, wherein the first amount of reducing agent is provided using at least two injectors.

In accordance with a further embodiment, disclosed herein is a method of retrofitting a boiler, the boiler comprising a housing with a burner, an intermediate furnace, a convection section downstream of the furnace, and a flue gas outlet downstream of the convection section, with a NOxremoval system.

In accordance with a further embodiment, disclosed herein is a method of retrofitting a boiler, the boiler comprising a housing with a burner, an intermediate furnace, a convection section downstream of the furnace, and a flue gas outlet downstream of the convection section, with a NOxremoval system, the method comprising determining one or more parameters of the boiler, wherein at least one of the one or more parameters is selected from the group consisting of internal shape of the boiler or other fired vessel, internal shape of the furnace, internal shape of the convection section, internal shape of the flue gas outlet, peak temperature of the furnace, peak temperature of the convection section, peak temperature of the flue gas outlet, operable temperature range of the furnace, operable temperature range of the convection section, operable temperature range of the flue gas outlet, concentration range of NOxformation, operable firing range, type of NOxcompounds and concentration range of one or more types of NOxcompounds, operating conditions causing peak NOxformation and combinations thereof; determining one or more parameters of a NOxremoval system, wherein at least one of the one or more parameters is selected from the group consisting of SCR catalyst to be used, reducing agent to be used, number of reducing agent loading points, locations of reducing agent loading points, type of means for loading reducing agent, timing of reducing agent loading at each reducing agent loading point, concentration of reducing agent loading at each reducing agent loading point, spray pattern of the means for loading reducing agent at each reducing agent loading point, dilution or dilution range of the reducing agent, and combinations thereof; providing, based on the one or more parameters of the NOxremoval system, a first means in communication with the housing for providing a reducing agent into the housing of the boiler downstream of the furnace, wherein the first means comprises at least two injectors; providing, based on the one or more parameters of the NOxremoval system, a second means in communication with the housing for providing a reducing agent into the housing of the boiler downstream of the first means for providing reducing agent; and providing, based on the one or more parameters of the NOxremoval system, a selective catalytic reduction catalyst downstream from or simultaneously with the second means for providing a reducing agent.

