Low emission modular flare stack

Abstract

A low emissions modular flare stack includes a plurality of flare stack burner modules, each including a main fuel source configured to selectively deliver a main fuel stream for dilution by a flow of combustion air, a main igniter configured to cause ignition of the main fuel stream emitted from the main fuel source, a distal flame holder configured to hold a combustion reaction supported by the main fuel stream when the distal flame holder is at or above a predetermined temperature, and a pre-heating apparatus configured to pre-heat the distal flame holder to the predetermined temperature. The low emissions modular flare stack includes a common combustion air source configured to provide combustion air to each of the plurality of flare stack burner modules, and a wall encircling all of the plurality of flare stack burner modules, the wall being configured to laterally contain combustion products corresponding to all of the plurality of flare stack burner modules.

1 . A low emissions modular flare stack, comprising:
 a plurality of flare stack burner modules, each flare stack burner module including:
 a main fuel source, separately valved from all other fuel sources, configured to selectively deliver a stream of a main fuel for dilution by a flow of combustion air, 
 a main fuel igniter configured to cause ignition of the main fuel emitted from the main fuel source, 
 a distal flame holder, separated from the main fuel source and the main fuel igniter by respective non-zero distances, the distal flame holder being configured to hold a combustion reaction supported by the main fuel when the distal flame holder is at or above a predetermined temperature, and 
 a pre-heating apparatus configured to pre-heat the distal flame holder to the predetermined temperature; 
   a common combustion air source configured to provide combustion air to each of the plurality of flare stack burner modules; and   a wall encircling all of the plurality of flare stack burner modules, the wall being configured to laterally contain combustion fluids.   
     
     
         2 . The low emissions modular flare stack of  claim 1 , wherein the predetermined temperature is equal to or greater than a main fuel auto-ignition temperature. 
     
     
         3 . The low emissions modular flare stack of  claim 1 , wherein the pre-heating apparatus of each flare stack burner module comprises a continuous pilot burner configured to guarantee combustion of the main fuel. 
     
     
         4 . The low emissions modular flare stack of  claim 3 , wherein
 the continuous pilot burner is configured to selectively output heat at any of a plurality of heating rates,   at least one heating rate is selected to cause a rise in sensible temperature of the distal flame holder to the predetermined operating temperature; and   at least one other heating rate is selected to cause the pre-heating apparatus to maintain a pilot flame function while a majority of total fuel consumed per unit time is provided by the main fuel source.   
     
     
         5 . (canceled) 
     
     
         6 . The low emissions modular flare stack of  claim 1 , wherein the common combustion air source is configured to provide natural draft combustion air to each flare stack burner module of the plurality of flare stack burner modules. 
     
     
         7 . The low emissions modular flare stack of  claim 1 , further comprising:
 a respective plurality of separate valves, each including an actuator configured to operate responsive to receiving control signals; and   a control system configured to output respective control signals to each of the separate valve actuators;   wherein the control system further comprises:
 an interface between the control system and an input channel, wherein the interface is configured to receive a signal corresponding to a flare stack capacity requirement; 
 one or more flare stack burner module sensor inputs, each of the one or more flare stack burner module sensor inputs being configured to receive a signal corresponding to a flare stack burner module status wherein the flare stack burner module status is provided by sensor hardware; 
 a microcontroller, a computer readable memory, and a module sequencer configured to select a subset of the plurality of flare stack burner modules for ignition; and 
 a respective plurality of main fuel valve driver outputs each operatively coupled to one of the separately actuated main fuel valves. 
   
     
     
         8 . The low emissions modular flare stack of  claim 7 , wherein the control system further comprises one or more of:
 a module sequencer configured to changeably sequence an actuation of the flare stack burner modules;   a run sequencer including a state machine configured to sequence steps in a start-up schedule of the flare stack burner modules;   an actuator driver module configured to provide the respective control signals to each of the separate valve actuators; and   a demand module configured to supervise automatic operation of the flare stack burner modules selectively based on at least one of a stored schedule and a received demand signal.   
     
     
         9 .- 11 . (canceled) 
     
     
         12 . The low emissions modular flare stack of  claim 7 , wherein the microcontroller is configured to read and execute computer executable instructions, supported by a non-transitory computer readable memory, to:
 receive capacity input data corresponding to the flare stack capacity requirement signal;   read module status sensor data corresponding to at least one flare stack to verify that a selected one of the flare stack burner modules is ready for firing;   select the subset of the plurality of flare stack burner modules for firing; and   drive at least one of the separate valve actuators corresponding to the subset of the selected plurality of flare stack burner modules to open so as to provide fuel to a combustion reaction supported by the subset of the plurality of flare stack burner modules.   
     
     
         13 .- 14 . (canceled) 
     
     
         15 . The low emissions modular flare stack of  claim 1 , wherein each of the plurality of flare stack burner modules further comprises:
 a pilot fuel source configured to provide a pilot fuel to the pre-heating apparatus, and   a pilot fuel igniter configured to ignite a flow of the pilot fuel, and   wherein the pre-heating apparatus includes a distal pilot configured to hold a pilot flame supported by the pilot fuel, a pilot fuel source flow rate being selected to provide a pilot flame sized to raise the distal flame holder temperature to the pre-determined temperature.   
     
     
         16 . (canceled) 
     
     
         17 . The low emissions modular flare stack of  claim 15 , wherein the main fuel igniter comprises the distal pilot. 
     
     
         18 . The low emissions modular flare stack of  claim 15 , wherein the main fuel igniter comprises the distal flame holder when the distal flame holder is heated to the pre-determined temperature by the distal pilot. 
     
     
         19 . The low emissions modular flare stack of  claim 15 , wherein the distal pilot is configured to be controlled to provide the pilot flame sized to raise the distal flame holder to the pre-determined temperature during a flare stack burner module start-up cycle, and to not provide the pilot flame sized to raise the distal flame holder to the pre-determined temperature at times other than during the flare stack burner module start-up cycle. 
     
     
         20 .- 23 . (canceled) 
     
     
         24 . The low emissions modular flare stack of  claim 15 , wherein at least one of the main fuel and the pilot fuel is a hydrocarbon condensate. 
     
     
         25 . (canceled) 
     
     
         26 . The low emissions modular flare stack of  claim 15 , wherein the pilot fuel is natural gas or propane. 
     
     
         27 . The low emissions modular flare stack of  claim 1 , wherein:
 the wall constitutes at least part of a housing having a combustion air inlet at a base;   the main fuel source includes an inlet configured to be coupled to a waste fuel supply;   the common combustion air source is positioned to receive the combustion air via the housing;   the distal flame holder is positioned inside the housing; and   the main fuel source includes a main nozzle configured to receive a flow of at least the waste fuel as a main fuel from the inlet, and to emit Hall the main fuel stream toward the distal flame holder.   
     
     
         28 . The low emissions modular flare stack of  claim 27 , wherein each of the flare stack burner modules is configured to be freestanding, supported only by a coupling at the inlet. 
     
     
         29 . The low emissions modular flare stack of  claim 27 , wherein each of the flare stack burner modules is configured to be coupled to the flare stack wall and to be supported thereby. 
     
     
         30 . The low emissions modular flare stack of  claim 27 , wherein the main nozzle is one of a plurality of main nozzles respectively corresponding to each flare stack burner module, each of the main nozzles being configured to receive a flow of the main fuel from the inlet, and to respectively emit the main fuel stream toward a respective portion of the distal flame holder. 
     
     
         31 . The low emissions modular flare stack of  claim 30 , further comprising a plurality of main fuel valves operatively coupled between a common fuel line and a respective one of the plurality of main nozzles and configured to independently control operation of the respective main nozzle. 
     
     
         32 . (canceled) 
     
     
         33 . The low emissions modular flare stack of  claim 3 , wherein each continuous pilot includes a plurality of pilot fuel nozzles arranged in an array. 
     
     
         34 . (canceled) 
     
     
         35 . The low emissions modular flare stack of  claim 27 , wherein the main nozzle includes an aperture having a size that is variable. 
     
     
         36 . The low emissions modular flare stack of  claim 35 , wherein the main nozzle is configured to regulate a velocity of the main fuel stream. 
     
     
         37 .- 39 . (canceled) 
     
     
         40 . A method of using a flare stack having a plurality of flare stack burner modules, the method comprising:
 outputting, toward a distal flame holder of each flare stack module of the plurality of flare stack burner modules, a waste gas and a supplemental fuel added to sufficiently raise a heating value of the waste gas plus the supplemental fuel to about 100 BTU per cubic foot or less; and   combusting the waste gas and the supplemental fuel substantially within one or more of the plurality of flare stack burner modules.   
     
     
         41 . The method of  claim 40 , wherein the combusting of the waste gas comprises emitting a fuel stream that includes the waste gas from a main nozzle positioned within one of the flare stack burner modules of the flare stack and toward a distal flame holder of the one of the flare stack burner modules. 
     
     
         42 . The method of  claim 41 , further comprising, prior to performing the combusting of the waste gas, pre-heating the distal flame holder by operating a distal pilot positioned within the flare stack burner module. 
     
     
         43 . The method of  claim 42 , further comprising, after performing the pre-heating of the distal flame holder:
 shutting off a flow of pilot fuel to the distal pilot; and   introducing a flow of main fuel to the main nozzle of the one of the flare stack burner modules.   
     
     
         44 . The method of  claim 41 , wherein the emitting the main fuel stream from the main nozzle positioned within the one of the flare stack burner modules is comprised by emitting a main fuel stream from each of a plurality of main nozzles positioned within the flare stack burner module, each toward a respective portion of the distal flame holder of the corresponding flare stack burner module. 
     
     
         45 . The method of  claim 44 , wherein the emitting the main fuel stream from each of the plurality of main nozzles positioned within the flare stack burner module comprises selecting the main nozzles of a number of the plurality of flare stack burner modules based upon a volume of waste gas to be combusted. 
     
     
         46 . The method of  claim 45 , wherein the selecting the main fuel nozzles of the number of the plurality of main nozzles of a number of the plurality of flare stack burner modules based upon the volume of waste gas to be combusted comprises varying the number of the plurality of flare stack burner modules in response to changes in the volume of waste gas. 
     
     
         47 .- 56 . (canceled) 
     
     
         57 . The low emissions modular flare stack of  claim 15 , wherein the distal pilot includes one or more pilot fuel nozzles, each pilot fuel nozzle defining a plurality of fuel orifices have a large collective area to collectively support a low momentum pilot flame. 
     
     
         58 . (canceled) 
     
     
         59 . The low emissions modular flare stack of  claim 57 , wherein the plurality of fuel orifices are disposed across the flare stack burner module volume sufficiently broadly to cause contact of the pilot flame with the main fuel and combustion air mixture across the breadth of the combustible mixture. 
     
     
         60 . (canceled) 
     
     
         61 . The low emissions modular flare stack of  claim 15 , wherein the distal pilot includes a single pilot fuel nozzle comprising a fuel manifold having a plurality of segments joined together, each segment having a plurality of fuel orifices configured to pass fuel from inside the fuel manifold to a flare stack burner module combustion volume. 
     
     
         62 . The low emissions modular flare stack of  claim 61 , wherein the plurality of segments are formed as respective tubes configured to freely pass the pilot fuel delivered from a pilot fuel pipe into the fuel manifold. 
     
     
         63 . (canceled) 
     
     
         64 . The low emissions modular flare stack of  claim 27 , wherein the pre-heating apparatus forms a second fuel dump plane at a distal location at least 100 main fuel nozzle diameters from a bottom of the respective flare stack burner module of the plurality of flare stack burner modules. 
     
     
         65 .- 68 . (canceled) 
     
     
         69 . The low emissions modular flare stack of  claim 1 , further comprising support legs supporting the distal flame holder in each flare stack burner module. 
     
     
         70 . (canceled) 
     
     
         71 . A method for operating a flare stack burner module having a distal flame holder, comprising:
 providing heat to the distal flame holder with a pilot flame holder, the distal flame holder and the pilot flame holder being disposed in the flare stack burner module and in proximity to one another;   introducing main fuel and combustion air to the pilot flame holder and the distal flame holder; and   holding at least a portion of a combustion reaction of the main fuel and combustion air at the distal flame holder while the pilot flame holder remains lit.   
     
     
         72 . (canceled)