Process for corrosion control in boilers

Abstract

A corrosion control process is described. The process is especially useful in the control of chloride corrosion in waste to energy boilers. Corrosion of high temperature surfaces can be assessed by the monitor and controlled introduction of treatment chemicals by targeted in furnace injection reduces corrosion while maximizing combustion efficiency. A corrosion monitor is also described. Before and following selection of corrosion control chemicals and the locations for targeted in furnace injection, injection regimen and chemical selection and introduction parameters are monitored with the aid of the method and apparatus of the invention to adjust one or more control parameters to reduce corrosion. A preferred method will employ a treatment chemical that comprises an SO 2 or SO 3 reagent, e.g., sulfuric acid, sulfur, a sulfate salt or a bisulfite salt.

1 . A process for corrosion control in a boiler which comprises: monitoring corrosion within a boiler having a corrosive atmosphere and introducing treatment chemicals containing SO 2  or SO 3  or precursors therefor at positions selected in response to monitored corrosion, to thereby modulate or prevent the problems of high temperature corrosion of metal surfaces.  
     
     
         2 . A process according to  claim 1 , wherein: a constant temperature probe having a corrodible surface is positioned in a known position in a boiler; the probe is periodically removing for visual and/or physical observation; based on the observations of the probe and comparison with data for boiler components such as tubes, the degree of corrosion on the probe is calibrated with what could be expected of the boiler components; and then the observations of the probe as calibrated are utilized to control introduction of corrosion control chemicals into the boiler.  
     
     
         3 . A process according to  claim 1 , wherein: the degree of corrosion in a boiler is monitored utilizing a probe and signal processor for observing electrochemical noise in a probe within the furnace and comparing that information to known values to provide a signal that corresponds to corrosion rate.  
     
     
         4 . A process according to  claim 3 , wherein: the probe is a constant temperature probe.  
     
     
         5 . A process according to  claim 1  wherein the boiler is a waste to energy boiler.  
     
     
         6 . A process according to  claim 1 , wherein: probes for a corrosion monitor are placed in original positions and the original introduction parameters for the introduction of corrosion control chemicals are based on computational fluid dynamic determinations.  
     
     
         7 . A process according to  claim 1 , wherein: a chemical composition comprising an SO 2  or SO 3  or precursor of either is introduced into the corrosive atmosphere in a manner effective to maintain chlorine gas in gaseous form and the sulfate salts of the metal being corroded in solid form.  
     
     
         8 . A process according to  claim 7 , wherein: the chemical composition comprising SO 2  or SO 3  or precursor of either comprises a sulfate salt, bisulfite salt, sulfuric acid, or sulfur in amounts sufficient to reduce corrosion.  
     
     
         9 . A process according to  claim 8 , wherein: the corrodible surface of said probe is subjected to periodic UT measurements and to metallographic analysis and physical measurement of metal thickness remaining.  
     
     
         10 . A process according to  claim 1 , wherein: corrosion is monitored by use of a probe capable of fixing to a boiler exterior and extending into a boiler to an extent necessary to reach a suspected trouble point for corrosion; a source of cooling fluid and means for directing the fluid into the probe for cooling the probe; and temperature sensing means associated with the probe and control means for controlling supply of the fluid to the probe; wherein the probe is adapted to permit insertion and withdrawal from the boiler for visual and physical observation.  
     
     
         11 . A method for monitoring corrosion on a real time basis and under operational conditions for boilers, where high temperature corrosion is a problem, comprising: 
 disposing an apparatus comprising a cooled, probe having a corrodible portion with means to sense the temperature of the probe and the surroundings in a predetermined operable position in a boiler;    periodically removing the probe for visual and/or physical observation;    based on the observations of the probe and comparison with data for boiler components such as tubes, calibrating the degree of corrosion on the probe with what could be expected of the boiler components; and    utilizing observations of the probe as calibrated to determine the degree of corrosion of metal surfaces near the predetermined location of the probe.    
     
     
         12 . A method according to  claim 11  wherein the boiler is a waste to energy boiler.  
     
     
         13 . A method according to  claim 11  wherein corrosion observed by use of the probe are used to set or adjust introduction of treatment chemicals for the purpose of modulating or preventing the problems of high temperature corrosion of metal surfaces.  
     
     
         14 . A method according to  claim 11  wherein the treatment chemical comprises SO 2  or SO 3  or precursor of either.  
     
     
         15 . A process according to  claim 14 , wherein: the chemical composition comprising SO 2  or SO 3  or precursor of either comprises a sulfate salt, bisulfite salt, sulfur or sulfuric acid, in amounts sufficient to reduce corrosion.  
     
     
         16 . An apparatus of the invention provides a constant temperature metal sample that can be exposed to operating conditions in a WTE boiler and removed on-line and be subjected to UT measurements frequently, e.g., such as weekly and then after a longer period of exposure, e.g., 25-30 days, be sent to a laboratory for detailed metallographic analysis and physical measurement of metal thickness remaining.  
     
     
         17 . A corrosion control process for monitoring corrosion on a real time basis and under operational conditions for boilers, where high temperature corrosion is a problem, comprising: 
 determining initial placement of one or more probes as described in  claim 5  in a operable position in a boiler and initial introduction parameters for the introduction of corrosion control chemicals through the use of computational fluid dynamics;    periodically removing the probe for visual and/or physical observation; based on the observations of the probe and comparison with data for boiler components such as tubes, calibrating the degree of corrosion on the probe with what could be expected of the boiler components; and    utilizing observations of the probe as calibrated to control introduction of corrosion control chemicals into the boiler.    
     
     
         18 . A method according to  claim 17  wherein the treatment chemical comprises SO 2  or SO 3  or precursor of either.  
     
     
         19 . A process according to  claim 18 , wherein: the chemical composition comprising SO 2  or SO 3  or precursor of either comprises a sulfate salt, bisulfite salt, sulfur, or sulfuric acid, in amounts sufficient to reduce corrosion.  
     
     
         20 . An apparatus for determining corrosion in a boiler, comprising: a probe capable of being fixed to a boiler exterior and extending into a boiler to an extent necessary to reach a suspected trouble point for corrosion; a source of cooling fluid and means for directing the fluid into the probe for cooling the probe; temperature sensing means associated with the probe; and control means for controlling supply of the fluid to the probe.