Processes for Managing Combustion of a Fuel Gas Supplied to a Combustion Zone

Abstract

Processes for managing combustion of a fuel gas in the presence of an oxidant supplied to a combustion zone, where the fuel gas undergoes an event that includes a pressure decrease and/or an average molecular weight increase, and where the fuel gas is supplied to the combustion zone via a valve. The process can include (I) detecting the event. Upon detecting the event in step (I), the process can also include (II-a) controlling the fuel gas supplied to the combustion zone by limiting an output of the valve to no more than a predetermined threshold output to prevent excessive fuel gas flooding the combustion zone and/or (II-b) controlling the fuel gas supplied to the combustion zone by adjusting the valve to maintain a pressure of the fuel gas after the valve to no higher than a predetermined threshold pressure to prevent excessive fuel gas flooding the combustion zone.

What is claimed is: 
     
         1 . A process for managing combustion of a fuel gas in the presence of an oxidant supplied to a combustion zone, wherein the fuel gas may undergo an event including pressure decrease and/or average molecular weight increase, and wherein the fuel gas is supplied to the combustion zone via a fuel gas valve, the process comprising:
 (I) detecting the event; and subsequently carrying out (II-a) and/or (II-b) below:   (II-a) controlling the fuel gas supplied to the combustion zone by limiting an output of the fuel gas valve to no more than a predetermined threshold output to prevent excessive fuel gas flooding the combustion zone; and   (II-b) controlling the fuel gas supplied to the combustion zone by adjusting the fuel gas valve to maintain a pressure of the fuel gas after the fuel gas valve to no higher than a predetermined threshold pressure to prevent excessive fuel gas flooding the combustion zone.   
     
     
         2 . The process of  claim 1 , wherein:
 before the event, the fuel gas is a H 2 -rich fuel gas at a first pressure,   during the event, the fuel gas changes from the H 2 -rich fuel gas to a backup fuel gas, and   the backup fuel gas has an average molecular weight greater than an average molecular weight of the H 2 -rich fuel.   
     
     
         3 . The process of  claim 2 , wherein the backup fuel gas comprises one or more C 1 -C 4  hydrocarbons and comprises less H 2  than the H 2 -rich fuel gas. 
     
     
         4 . The process of  claim 2 , wherein the backup fuel gas comprises natural gas, a methane-rich gas, an ethane-rich gas, a propane-rich gas, a butane-rich gas, or a mixture thereof. 
     
     
         5 . The process of any one of  claims 2 to 4 , wherein:
 step (I) comprises monitoring a backup fuel valve in fluid communication with an inlet side of the fuel gas valve that supplies the fuel gas to the combustion zone,   the backup fuel valve is configured to introduce the backup fuel gas into the fuel gas valve upon opening of the backup fuel valve, and   detecting the event in step (I) comprises detecting the backup fuel valve opening.   
     
     
         6 . The process of any one of  claims 1 to 5 , wherein step (II-a) is carried out, and wherein the predetermined threshold output is determined based on at least one of: a density of the fuel gas supplied to the combustion zone upon the detection of the event, an average molecular weight of the fuel gas supplied to the combustion zone upon the detection of the event, and the fuel gas valve output before the event is detected. 
     
     
         7 . The process of any one of  claims 1 to 5 , wherein step (II-a) is carried out, and wherein the predetermined threshold output is a threshold output that was used after detecting one or more prior events. 
     
     
         8 . The process of any one of  claims 1 to 5 , wherein step (II-a) is carried out, and wherein the predetermined threshold output is arrived at over a period of time using a predetermined algorithm. 
     
     
         9 . The process of any one of  claims 1 to 5 , wherein step (II-b) is carried out, and wherein the predetermined threshold pressure is determined based on at least one of: a density of the fuel gas supplied to the combustion zone upon the detection of the event, an average molecular weight of the fuel gas supplied to the combustion zone upon the detection of the event, and the pressure of the fuel gas before the event is detected. 
     
     
         10 . The process of any one of  claims 1 to 5 , wherein step (II-b) is carried out, and wherein the predetermined threshold pressure is a threshold pressure that was used after detecting one or more prior events. 
     
     
         11 . The process of any one of  claims 1 to 5 , wherein step (II-b) is carried out, and wherein the predetermined threshold pressure is arrived at over a period of time using a predetermined algorithm. 
     
     
         12 . The process of any one of  claims 1 to 4 , wherein step (I) comprises monitoring one or more process parameters and detecting a change in the one or more monitored process parameters. 
     
     
         13 . The process of  claim 12 , wherein step (II-a) is carried out and detecting the change in the one or more monitored process parameters comprises detecting an increased opening of the fuel gas valve. 
     
     
         14 . The process of  claim 13 , further comprising measuring a density of the fuel gas or an average molecular weight of the fuel gas supplied to the combustion zone upon detection of the event, wherein the predetermined threshold output is determined based on the measured density of the fuel gas or the measured average molecular weight of the fuel gas. 
     
     
         15 . The process of  claim 13 , wherein the predetermined threshold output is a threshold output that was used after detecting one or more prior events. 
     
     
         16 . The process of  claim 12 , wherein step (II-b) is carried out and detecting the change in the one or more monitored process parameters comprises detecting a reduction in a pressure of the fuel gas upstream of the fuel gas valve. 
     
     
         17 . The process of  claim 16 , wherein the predetermined threshold pressure is a threshold pressure that was used after detecting one or more prior events. 
     
     
         18 . The process of  claim 16 , further comprising measuring a density of the fuel gas or an average molecular weight of the fuel gas supplied to the combustion zone upon the detection of the event, wherein the predetermined threshold pressure is determined based on the measured density or the measured average molecular weight. 
     
     
         19 . The process of  claim 12 , wherein:
 before the event, the fuel gas is supplied from a H 2  supply source, a hydrogen recovery unit in a petrochemical plant, or a tail gas produced from a recovery section of an olefins production plant, and   detecting the change in the one or more monitored process parameters comprises detecting one or more of the following: a trip signal from the H 2  supply source, a trip signal from the hydrogen recovery unit in the petrochemical plant, a trip signal of a process gas compressor, or a trip signal of a turbo-expander supplying the tail gas.   
     
     
         20 . The process of any one of  claims 1 to 19 , wherein carrying out step (II-a) or step (II-b) maintains an amount of O 2  within the combustion zone that is at least 0.5 mol % greater than an amount of O 2  required to combust the fuel gas introduced into the combustion zone after the event is detected. 
     
     
         21 . The process of any one of  claims 1 to 20 , wherein the oxidant is supplied to the combustion zone via an induced draft fan or a forced draft fan, the process further comprising:
 (III) when the event is detected in step (I), controlling the oxidant supplied to the combustion zone by adjusting a parameter of the induced draft fan or the forced draft fan to maintain a flow rate of the oxidant into the combustion zone above a predetermined lower limit.   
     
     
         22 . The process of any one of  claims 1 to 21 , wherein a rate of change of the pressure decrease is >10% per minute and/or a rate of change of the average molecular weight increase is >10% per minute. 
     
     
         23 . The process of any one of  claims 1 to 22 , wherein:
 the fuel gas and the oxidant are supplied to two or more combustion zones,   the fuel gas is supplied to each of the two or more combustion zones via a corresponding fuel gas valve, and   upon detecting the event, step (II-a) is carried out such that the output of each corresponding fuel gas valve is limited to no more than the predetermined threshold output and/or step (II-b) is carried out such that each corresponding fuel gas valve is adjusted to maintain the pressure of the fuel gas after the fuel gas valve to no higher than the predetermined threshold pressure.   
     
     
         24 . The process of any one of  claims 1 to 23 , wherein step (II-a) and/or step (II-b) is carried out automatically. 
     
     
         25 . The process of any one of  claims 1 to 24 , wherein step (II-a) is carried out, the process further comprising using a predetermined period of time, a fuel gas header condition, or a combination thereof to return the threshold output of the fuel gas valve to an initial value that was used prior to detecting the event. 
     
     
         26 . The process of any one of  claims 1 to 24 , wherein step (II-b) is carried out, the process further comprising using a predetermined period of time, a fuel gas header condition, or a combination thereof to return the threshold pressure to an initial value that was used prior to detecting the event. 
     
     
         27 . A process, comprising:
 introducing a fuel gas via a fuel gas valve and an oxidant-containing feed via an induced draft fan or a forced draft fan into a combustion zone of a furnace;   contacting at least a portion of the fuel gas with at least a portion of the oxidant-containing feed before or within the combustion zone to effect combustion within the combustion zone of at least a portion of the fuel gas to produce a combustion effluent;   monitoring one or more process parameters during the introduction and combustion of the fuel gas;   determining, based on the one or more monitored process parameters, the fuel gas has undergone an event comprising at least one of a pressure decrease and an average molecular weight increase; and   controlling the fuel gas introduced into the combustion zone by (i) limiting an output of the fuel gas valve to no more than a predetermined threshold output to prevent excessive fuel gas flooding the combustion zone or (ii) adjusting the fuel gas valve to maintain the pressure of the fuel after the fuel gas valve to no higher than a predetermined threshold pressure to prevent excessive fuel gas flooding the combustion zone.