Dynamic control of selective non-catalytic reduction system for semi-batch-fed stoker-based municipal solid waste combustion

Abstract

The present invention controls reagent flow levels in a selective non-catalytic reduction (SNCR) system by more accurately predicting Nitrogen Oxides (NOx) production with a municipal waste combustor. In one embodiment, the reagent levels correspond with measured furnace temperatures. The reagent levels may have a baseline level from prior measured NOx that is then modified according to temperatures measurements. A slow controller may use NOx measurements over an extended period to define a base regent level, and a fast controller may use additional information such as the furnace temperature to modify the base regent level. The fast controller may further receive two additional signals that are added individually or together to maximize NOx control while minimizing ammonia slip from the reagent. The two signals are a feed-forward signal from the combustion controller and a feedback signal from an ammonia analyzer downstream of the combustion zone.

1 . A system for controlling NO x  levels comprising:
 a temperature sensor;   an amount of reagent for reducing NO x  levels;   a reagent supplier;   a reagent controller connected to the reagent supplier adapted to receive temperature data from the temperature sensor;   wherein the reagent controller is configured to adjust the amount of reagent based solely upon the temperature data obtained from the temperature sensor.   
   
   
       2 . The system of  claim 1 , wherein the system does not contain any components to measure NO x  levels directly. 
   
   
       3 . The system of  claim 1 , wherein the system is a SNCR system. 
   
   
       4 . The system of  claim 1 , wherein the system is a SCR system. 
   
   
       5 . The system of  claim 4 , wherein the temperature sensor is not configured to measure the catalyst temperature. 
   
   
       6 . The system of  claim 1 , wherein the temperature sensor is configured to measure the temperature of a furnace. 
   
   
       7 . The system of  claim 6 , wherein the furnace is configured to receive an amount of fuel and contains a flue and a grate for moving the fuel through the furnace. 
   
   
       8 . The system of  claim 1 , wherein the temperature sensor is a pyrometer. 
   
   
       9 . The system of  claim 1 , wherein the temperature sensor is configured to measure the temperature of gases in the furnace. 
   
   
       10 . The system of  claim 1  further comprising:
 a combustion controller connected to the reagent controller, wherein the combustion controller is configured to provide combustion data relating to combustion conditions upstream of the reagent controller.   
   
   
       11 . A system for controlling emission levels of NO x  comprising:
 a. a reagent controller;   b. a furnace for receiving an amount of fuel, said furnace containing a flue and a grate for moving the fuel through the furnace;   c. a continuous emissions monitoring (CEM) system comprising:
 i. a probe for determining one or more of the composition of pollutants, NO x  levels, or levels of un-reacted reagents emitted by the furnace; 
 ii. a link to the reagent controller for providing information on one or more of the pollutants, NO x  levels, or un-reacted reagents contained in the emissions from the furnace; 
   d. a temperature sensor for providing temperature information;   e. a combustion controller to monitor the amount of fuel entering the furnace and transfer this information to the reagent controller;   f. wherein the reagent controller has programmable logic stored on computer readable media for causing the reagent controller to perform the step of controlling reagent supply to the furnace based upon one or more of the CEM information, the combustion information or the temperature information.   
   
   
       12 . The system of  claim 11 , wherein the system is a SNCR system. 
   
   
       13 . The system of  claim 11 , wherein the system is a SCR system. 
   
   
       14 . The system of  claim 11 , wherein the CEM probe is positioned inside the furnace downstream of the flue. 
   
   
       15 . The system of  claim 11 , wherein the reagent controller has programmable logic stored on computer readable media for causing the reagent controller to perform the step of distributing the reagent into an area of high turbulence to homogenize distribution of the reagent in the furnace based upon information received from the CEM system. 
   
   
       16 . The system of  claim 11 , wherein the reagent controller has programmable logic stored on computer readable media for causing the reagent controller to perform the step of distributing the reagent when the temperature is high enough to allow NO x  to react with the reagent. 
   
   
       17 . The system of  claim 11 , wherein the CEM system comprises a first probe for determining NO x  levels and a second probe for determining ammonia slip levels. 
   
   
       18 . The system of  claim 17 , wherein the link is capable of transmitting a signal containing information on both the NO x  levels and the ammonia slip levels. 
   
   
       19 . The system of  claim 11 , wherein the combustion controller comprises an output for informing the reagent controller when additional fuel or additional air enters the furnace. 
   
   
       20 . A method for controlling emission levels of NO x  comprising the steps of:
 a. providing a reagent controller;   b. receiving an amount of fuel in a furnace containing a flue and a grate;   c. using the grate to move the fuel into the furnace;   d. providing a continuous emissions monitoring (CEM) system; said CEM system:
 i. analyzing data received from a probe to determine one or more of the composition of pollutants, NO x  levels, or levels of un-reacted reagents emitted by the furnace; 
 ii. providing information on one or more of the pollutants, NO x  levels, or levels of un-reacted reagents contained in the emissions from the furnace to the reagent controller; 
   g. providing a temperature sensor that provides the reagent controller with temperature information;   e. providing a combustion controller to monitor the amount of fuel entering the furnace and transfer this information to the reagent controller;   f. wherein the reagent controller has a programmable logic stored on computer readable media for causing the reagent controller to perform the step of controlling the amount of reagent supplied to the furnace based upon one or more of the temperature information, the information received from the CEM system and the information received from the combustion controller.