Title of Invention	A SYSTEM FOR WASTE HEAT DRIVEN COMBUSTION TURBINE INLET AIR COOLING
Abstract	High efficiency fully automatic safe and reliable compact blast furnace gas fired steam boiler comprising of refractory lined combustion chamber for combustion of BFG with air staged axial swirl type BFG burners provided for burning of BFG at front end; smoke tube type evaporator provided for steam generation installed at the exit of combustion chamber; pilot fuel burner provided at front end of combustion chamber for cold start of BFG combustion chamber which can act as stand by burner as well; the balanced draft system comprising of forced draft fan, dilution air fan, induced draft fan, gas ducting and draft control system; gas train provided for regulations and modulation of blast furnace gas flow and pressure into the combustion chamber; instruments, controls and safeties for automatic and reliable operation of the boiler.

Title of Invention

A SYSTEM FOR WASTE HEAT DRIVEN COMBUSTION TURBINE INLET AIR COOLING

Abstract

High efficiency fully automatic safe and reliable compact blast furnace gas fired steam boiler comprising of refractory lined combustion chamber for combustion of BFG with air staged axial swirl type BFG burners provided for burning of BFG at front end; smoke tube type evaporator provided for steam generation installed at the exit of combustion chamber; pilot fuel burner provided at front end of combustion chamber for cold start of BFG combustion chamber which can act as stand by burner as well; the balanced draft system comprising of forced draft fan, dilution air fan, induced draft fan, gas ducting and draft control system; gas train provided for regulations and modulation of blast furnace gas flow and pressure into the combustion chamber; instruments, controls and safeties for automatic and reliable operation of the boiler.

Full Text	FORM-2 THE PATENTS ACT, 1970 COMPLETE SPECIFICATION (Section 10) 'HIGH EFFICIENCY COMPACT FULLY AUTOMATIC SAFE AND RELIABLE BLAST FURNACE GAS FIRED STEAM BOILER" ASHOK DATTATRAYA ATRE 'Pushpa heights', 1st floor, Bibwewadi Corner, PUNE- 411 037, MAHARASHTRA STATE, INDIA Indian National The following specification particularly describes the invention and the manner in which it is to be performed. FIELD OF THE INVENTION: Present invention relates to high efficiency compact fully automatic safe and reliable Blast Furnace Gas (BFG) Fired Steam Boiler. PRIOR ART: The known existing blast furnace gas fired boiler has following features- 1) The BFG Fired Boilers are either watertube type boilers or internal furnace firetube type boilers. 2) These BFG fired boilers need support of costly fuels in the form of either natural gas or petroleum oil to sustain the BFG flame. 3) The requirement of support fuel is typically upto 30% or even higher of the total heat input required for the boiler doe achieving required output capacity. Taking into consideration the known BFG fired boilers, following are the disadvantages- 1) BFG being a lean burning gas and due to peculiar construction of the furnace of these boilers, in many cases costly support fuel in the form of oil or natural gas is continuously required to be burnt to sustain the flame of BFG. 2) Due to peculiar construction of these boilers and BFG being a lean burning gas, during every restart, the boiler needs to be started under all circumstances with supporting fuel till the boiler furnace conditions is stabilized and the furnace achieves the temperature of typically 700 Deg. C or higher. The time required for stabilizing furnace conditions is very high which demands very high consumption of costly support fuel. -2- 3) In case of BFG fired watertube boilers which are essentially field erected, initial cost is very high as compared to the invention mentioned herein below. Hence many projects find investment in watertube boilers much less attractive compared to invention mentioned herein below. Due to this, BFG is even flared and burnt without use resulting in wastage of energy which is national loss. 4) The requirement of costly support fuel increases the running cost of the boiler, as the cost of oil / natural gas is substantially higher compared to BFG. Even if BFG is available with the user in sufficient quantity and at low cost, the same can not be fully utilized without continuous consumption of costly fuel. 5) Since the BFG can not be stored in large quantities, the excess BFG has to be flared and burnt in the atmosphere thereby resulting in substantial or nearly total loss of heat. This results on one side in colossal wastage of energy and on other side colossal consumption of costly petroleum fuels which is a national loss. 6) Additional investment in the form of support fuel burner, the fuel handling, storage and preparation is required. This further increases overall investment cost and weakens techno-economic feasibility. 7) Furnaces of watertube boilers not having membrane panel in the furnace are not water tight, hence in case of even minor leakage from the furnace of the BFG fired boiler, there exists fire, explosion hazards as well as health hazard due to leakage of unbumt BFG in the atmosphere. BFG contains poisonous Carbon Monoxide as a constituent in its components. -3- 8) The conventional BFG fired boilers do not have heat recovery units and are hence less efficient. 9) Furnace volume of "internal water cooled furnace" type firetube boilers is very much inadequate and hence continuous burning of substantial quantity of support fuel becomes a must for reliable continuous operation of BFG fired boiler. 10) There are severe capacities and output limitations on "internal furnace" type firetube boilers. Hence a battery having multiple boilers is needed to meet the requirements. This results in high initial cost as well as high operation and maintenance cost. Manpower needed to monitor boiler house is also much higher. PRESENT SECNARIO AND NEED OF THE PRESENT INVENTION: 1) Blast furnace gas (BFG) is byproduct of iron making process. It is the gas discharged from the steel mill blast furnace. It contains typically about 25% by volume poisonous and toxic Carbon Monoxide (CO). Its heating value is in the range of 600-700 kcal/Nm . Typical composition and its range is shown in Table I. 2) Conventionally in steel industries, the present design of available boilers has limitations mentioned here in above and here in below. 3) Since BFG has less calorific value it was not considered as a sole source of energy. -4- 4) Since support fuel is continuously used, whole amount of BFG is not utilized. Since the excess BFG can not be stored in large quantities; it has to be flared in the atmosphere without utilizing the heat content in the gas. This excess BFG can be utilized effectively if only BFG is used as fuel for steam generation, reducing the use of costly petroleum fuel. 5) If the boiler is used intermittently, at every start due to peculiar construction of the boiler, costly supporting fuel has to be used to attain steady state condition in combustion chamber. Thus in such case, the BFG can not be utilized effectively which results in increase of operating cost of the plant due to increase in use of costly supporting fuel. 6) Cost of conventional fuels like oil or natural gas has gone high and continues to rise at alarming rate. These fossil fuels are not environment friendly. Hence industries are searching for cheaper source of energy. 7) Since BFG is gas discharged from steel mill blast furnace, it is available readily at very low cost or no cost 8) Table 2 describes the savings possible if only BFG is used as fuel. It is therefore the objective of the new invention to develop a novel design which will eliminate above limitations and all BFG producing process and users can get benefited from the new design. -5- Table 1 Typical composition of Blast Furnace Gas (BFG) -6- Table 2. Typical savings possible with the use of newly invented Blast Furnace Gas (BFG) fired boiler No. Key Parameters Unit Existing Design New invention FOas support fuel LDO as support fuel HSD as support fuel NGas support fuel operated on 100 % BFG 1 Steam Generation capacity considered for comparison Metric Tons/hr from & at 100 DegC 10 10 10 10 10 2 Boiler heat input at 85% efficiency kcal/hr 6352941 6352941 6352941 6352941 6352941 3 Percentage of heat supplied by support fuel % 30 30 30 30 Nil 4 Heat given by support fuel kcal/hr 1905882 1905882 1905882 1905882 Negligible 5 Heat given by BFG kcal/hr 4447059 4447059 4447059 4447059 6352941 6 Calorific Value of support fuel Kcal/kg 9710 10210 10280 11400 NA 7 Calorific Value of BFG Kcal/kg 465 465 465 465 465 8 Typical amount of support fuel required Kg/hr 196 187 185 167 Nil 9 Amount of BFG required Kg/hr 9564 9564 9564 9564 13662 10 Amount of support fuel required per annum (based on 7000 hrs of working) Kg 1373963 1306677 1297780 1170279 Nil 11 Amount of BFG required per annum (based on 7000 hrs of working) Kg 66944972 66944972 66944972 66944972 95635674 12 Cost of fuel Rs/kg 14 21 33 9 Nil 13 Fuel cost per annum Rs./year 19235476 27440226 42826734 9947368 Nil 14 Fuel cost saved due to new Design Rs./year w.r.t. FO as fuel w.r.t. LDO as fuel w.r.t. HSD as fuel w.r.t. NG as fuel 1923547627440226428267349947368 Assumption: BFG is available as byproduct of steel mill and it is free of cost. FO: Furnace Oil; LDO: Light Diesel Oil; HSD: High Speed Diesel; NG: Natural Gas SUMMARY OF THE INVENTION: The present invention aims to provide a high efficiency compact BFG fired steam boiler. It is also the object of the present invention to provide the BFG fired boiler, which does not, require any support fuel except during cold start conditions which are very occasional. (Typically once or twice a year) It is also the object of the present invention to overcome and eliminate the drawbacks and shortfalls of the prior art. In the boiler of the present invention BFG is burnt in a separate combustion air cooled air tight steel sheet enclosed cylindrical refractory lined combustion chamber. The air required for combustion of BFG is supplied by a forced draft fan. A separate dilution air fan is also provided to maintain the flue gas temperature typically in the range of 1000 to 1200 Deg. C. This is done to protect certain types of refractory from getting overheated beyond its acceptable value. This temperature can be adjusted from design to design depending upon refractory material selected from those available. The flue gases are passed through a fire tube boiler and steam is generated. The flue gases leaving the boiler which are typically at a temperature of 300 to 400 Deg C are passed through an economizer where feed water is preheated typically from 90 Deg C upto saturation temperature at steam pressure. A steam superheater can also be provided as an optional device between boiler and economizer to suit the specific requirement. The combustion chamber, during use is continuously maintained under slightly negative pressure by an induced draft fan. The steam generation and steam pressure is controlled through a step less modulating control system. The flow of BFG into the combustion chamber is controlled through a gas train with all the necessary safeties and interlocks. A pilot gas or oil burner is provided only for the purpose of cold start of the boiler. The provision can also be made to operate the boiler folly or partially on oil or natural gas as stand-by fuels when BFG is not available fully or partially. BRIEF DESCRIPTION OF SCHEMATIC DRAWING: The invention is described with respect to accompanying Figure 1; having simplified flow diagram of newly invented high efficiency blast furnace gas fired steam boiler. DETAILED DESCRD7TION OF THE SCHEMATIC DRAWING: Referring to accompanying Figure 1, following components can be identified in the system. 1) BFG gas train 2) Combustion chamber 3) BFG burner 4) Pilot fuel burner 5) Smoke tube type evaporator 6) Economizer 7) Induced draft fan 8) Combustion air fan 9) Dilution air fan 10) Superheater (Optional) Blast furnace gas produced in the blast furnace enters the BFG gas train (marked as item no.l) after getting properly cleaned. The flow of BFG into the combustion chamber (marked as item no. 2) is controlled through the said gas train at steady automatically regulated preset pressure with all the necessary safeties and interlocks. Preset BFG pressure can be adjusted to suit the gas composition and desired firing condition and objectives. The said BFG gas train consists of water seal, pressure indicator and control valves. Water seal prevents the entry of BFG to the BFG furnace during shut down of -9- boiler. The controlled BFG flow then enters into the cylindrical shaped BFG combustion chamber (marked as item no.2). BFG burners (marked as item no.3) are provided on front side of combustion chamber in required and suitable numbers depending on needed firing rate and boiler capacity. These burners are arranged radially on the front wall of the said combustion chamber and pilot oil/gas burner (marked as item no.4) is provided at the centre. The said pilot burner is provided for the purpose of cold starting of the boiler. When the temperature in combustion chamber is reached beyond auto ignition temperature of BFG, the steady state in combustion chamber gets achieved. Once the steady state is achieved in boiler, the supply of support fuel to pilot burner is cut off. Now the flame is sustained with use of BFG only. Combustion air is supplied into the said combustion chamber with the help of combustion air fan (marked as item no.8). This combustion air is preheated by circulating it around the refractory lined combustion chamber. This preheated air not only provides effective cooling to refractory but it also assists the combustion of BFG in the said combustion chamber. Required dilution air supplied by dilution air fan (marked as item no.9) maintains the temperature of the said combustion chamber typically in the range of about 1100 to 1200 Deg C. The said combustion chamber is lined with refractory material. Refractory lined combustion chamber provides high thermal inertia which maintains the temperature of chamber above the auto ignition temperature of BFG. Thus only BFG can be used as a fuel to operate the combustion chamber. The thermal inertia provided by hot refractory is adequate for various firing rates that prevail at different steam generation rates depending on steam demands. The said BFG burners are placed at front end of combustion chamber. Each burner is of air staged axial swirl type. Burner consists of three concentric pipe sections. At front end of each stage i.e. pipe section, axial swirler fan is provided. Innermost pipe provided for air stage out of three concentric pipe sections provides path for primary air. Outermost sections provides path for secondary air. Middle section carries BFG. Blade orientation of -10- primary and secondary air is kept in same direction. Orientation of blades of BFG is kept in opposite direction with respect to that of primary and secondary air. Such type of arrangement creates enough intense turbulence for proper mixing of BFG and both stages of combustion air. The vanes for secondary air (outer stage) are designed for higher velocity. Due to this, the secondary air travels more distance in furnace. This assures the complete combustion of BFG. At the rear end of burner, suitable sizes of inlet nozzles are provided for primary air inlet and BFG inlet supply to burner. Secondary air directly passes from refractory shell to passage of secondary air (outer stage). The flue gases, generated by burning BFG are passed through a smoke tube evaporator (marked as item no.5) and steam is generated on shell side. The smoke tube evaporator is provided with the ferrules made of refractory materials to protect the tube to tube sheet welding joints from over heating due to hot gases entering into the furnace if any abnormal condition arises. The flue gases leaving the evaporator typically at a temperature of 300 to 400 Deg C are passed through an economizer (marked as item no .6) where feed water is preheated typically from 90 Deg C upto saturation temperature. A superheater (marked as item no. 10) can also be provided as an optional device between boiler and economizer to suit the specific requirement. Different interlocks and control valves are provided in the system for safety and reliability. Combustion chamber pressure is continuously and automatically maintained at set negative pressure through continuous modulation control system using pressure transmitter and PID controller, motorized air damper provided at suitable location in air and flue gas ducting respectively, frequency inverter driven forced draft and induced draft fans. The steam generation and steam pressure is controlled through a step less modulating control system using steam pressure transmitter and control valves to -11 - modulate burner firing rate and combustion air flow rate. The flow of dilution air is controlled continuously and automatically with the help of temperature indicator, PID and motorized damper. All these controls are properly interlocked for correct proportions of BFG and combustion air. Refer typical P & I diagram attached. The said BFG gas train is provided with water seal at the entry which controls BFG flow rate to the combustion chamber. The said smoke tube type evaporator is provided with level indicator, level transmitter, safety valve, and blow down valve. Following advantages are achieved by the present invention 1) Refractory lined combustion chamber provides high thermal inertia. Hence no supporting fuel is required to be burnt once the boiler achieves steady state of operation and the flame can be sustained with only BFG as fuel. 2) Supporting fuel is required only during cold start, which can be achieved by a pilot burner. 3) Due to high thermal inertia of refractory^ there is no requirement of support fuel even during automatic cut-in and cut-off operation of the boiler during partial low load conditions. 4) The running cost of the boiler is reduced substantially as there is no requirement of costly support fuel. 5) The BFG, if available in sufficient quantities, it can be completely utilized and no flaring in atmosphere is required. This not only reduces the running cost of the user but also reduces emission of green house gases and earns national wealth. -12- 6) The combustion air required for combustion of BFG is circulated over the refractory lined combustion chamber before it enters the combustion chamber. This air not only provides effective cooling to the refractory, thereby improving its life, but also provides pre-heated combustion air for BFG to assist combustion and improves combustion efficiency as well as reliability. 7) The smoke tube evaporator is provided with the ferrules made of refractory materials to protect the tube to tube sheet welding joints from over heating due to hot gases entering into the furnace. 8) Due to balanced draft system and sheet metal enclosure to combustion chamber, the entire combustion chamber is maintained reliably under slightly negative pressure and hence there is no possibility of leakage of carbon monoxide (CO) into the atmosphere during operation of the boiler. 9) Due to sheet metal enclosure of combustion chamber and due to circulation of combustion air around the refractory lined combustion chamber, BFG does not leak anytime and any operating condition into the atmosphere. Since combustion air jacket on refractory lined combustion chamber is under higher air pressure than combustion chamber, air injected will enter the combustion chamber but will not allow BFG to escape to the atmosphere even a crack or pinhole develops on combustion chamber on prolonged use. 10) With economizer as a heat recovery unit, the thermal efficiency of the boiler can be as high as 88% + 2% on net calorific value of fuel. -13- 11) To suit the specific requirement, the pilot burner can be designed to generate the full rated capacity of the boiler, when BFG is not available as fuel i.e. the same burner can act as support burner as well as standby burner. 12) The dilution air fan is provided to restrict the flue gas temperature typically in the range of 1000 to 1200 Deg. C to protect the tube to tube sheet welding joints of the main evaporator from over heating. This temperature after dilution can be adjusted and is controlled automatically and continuously through the use of PID and motorized dampen 13) Large number of safeties and interlocks are provided to ensure safe, reliable and automatic operation of the boiler. VARIATIONS POSSIBLE TO BE COVERED AND PROVIDED WITHIN THE INVENTION OF HIGH EFFICIENCY COMPACT BLAST FURNACE GAS FIRED STEAM BOILERS: 1. Various forms of heat output i.e. steam generation, Thermic fluid/hot oil generator, hot water generator, air/gas preheating, hot air generation etc. 2. Various steam generation heat generation capacities and outputs 3. Various working steam pressures 4. Various steam superheat temperatures 5. Various outlet temperatures of Thermic fluids, hot water hot air etc. 6. Various compositions of BFG and calorific values of BFG 7. Various refractory materials 8. Various types of heat exchangers/heat generators at outlet of BFG furnace viz. smoke tube type, coil type, watertube type, etc for different applications like steam generation, Thermic fluid/hot oil generator, hot water generator, air/gas preheating, hot air generation etc. -14- Claims: 1) High efficiency fiilly automatic safe and reliable compact blast fiimace gas fired steam boiler comprising of refractoiy lined combustion chamber for combustion of BFG with air staged axial swirl type BFG burners provided for burning of BFG at front end; smoke tube type evaporator provided for steam generation installed at the exit of combustion chamber; pilot fuel burner provided at front end of combustion chamber for cold start of BFG combustion chamber which can act as stand by burner as well; the balanced draft system comprising of forced draft fan, dilution air fan, induced draft fan, gas ducting and draft control system; gas train provided for regulations and modulation of blast furnace gas flow and pressure into the combustion chamber; instruments, controls and safeties for automatic and reliable operation of the boiler. 2) High efficiency fully automatic safe and reliable compact blast fiimace gas fired steam boiler as claimed in claim no. 1 wherein only BFG is used for steam generation. 3) High efficiency fiilly automatic safe and reliable compact blast fiimace gas fired steam boiler as claimed in claims no. 1 & 2 wherein, refractory lined combustion chamber is provided in which temperature is maintained above auto ignition temperature of BFG. 4) High efficiency fiilly automatic safe and reliable compact blast furnace gas fired steam boiler as claimed in claims no. 1, 2, & 3 wherein smoke tube type evaporator is used for steam generation. -15- 5) High efficiency fully automatic safe and reliable compact blast furnace gas fired steam boiler as claimed in claims no. 1, 2, 3 & 4 wherein the smoke tube evaporator is provided with the ferrules made of refractory materials. 6) High efficiency fully automatic safe and reliable compact blast furnace gas fired steam boiler as claimed in claims no. 1,2, 3,4 & 5 wherein air staged axial swirl type burner provided for burning BFG has three different paths for primary air, secondary air and BFG. 7) High efficiency fully automatic safe and reliable compact blast furnace gas fired steam boiler as claimed in claims no. 1, 2, 3,4, 5 & 6 wherein, combustion air is preheated around the shell of refractory lined BFG combustion chamber before entering BFG burner. 8) High efficiency fully automatic safe and reliable compact blast furnace gas fired steam boiler as claimed in claims no. 1, 2, 3,4, 5, 6 & 7 wherein, dilution air is supplied for maintaining the temperature of BFG furnace under safe limit. 9) High efficiency fully automatic safe and reliable compact blast furnace gas fired steam boiler as claimed in claims no. 1, 2, 3, 4, 5, 6 7, & 8 wherein, smoke tube type evaporator is provided with level indicator, level transmitter, safety valve, blow down valve. -16- 10) High efficiency folly automatic safe and reliable blast fomace gas fired steam boiler as claimed in claims no. 1, 2, 3, 4, 5, 6, 7, 8, & 9 above and herein described with respect to accompanying Figure no. 1. -17- ABSTRACT High efficiency fully automatic safe and reliable compact blast furnace gas fired steam boiler comprising of refractory lined combustion chamber for combustion of BFG with air staged axial swirl type BFG burners provided for burning of BFG at front end; smoke tube type evaporator provided for steam generation installed at the exit of combustion chamber; pilot fuel burner provided at front end of combustion chamber for cold start of BFG combustion chamber which can act as stand by burner as well; the balanced draft system comprising of forced draft fan, dilution air fan, induced draft fan, gas ducting and draft control system; gas train provided for regulations and modulation of blast furnace gas flow and pressure into the combustion chamber; instruments, controls and safeties for automatic and reliable operation of the boiler. -18-

Full Text

FORM-2
THE PATENTS ACT, 1970
COMPLETE SPECIFICATION (Section 10)
'HIGH EFFICIENCY COMPACT FULLY AUTOMATIC SAFE AND RELIABLE BLAST FURNACE GAS FIRED STEAM BOILER"
ASHOK DATTATRAYA ATRE
'Pushpa heights', 1st floor,
Bibwewadi Corner,
PUNE- 411 037, MAHARASHTRA STATE, INDIA
Indian National
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION:
Present invention relates to high efficiency compact fully automatic safe and reliable Blast Furnace Gas (BFG) Fired Steam Boiler.
PRIOR ART:
The known existing blast furnace gas fired boiler has following features-
1) The BFG Fired Boilers are either watertube type boilers or internal furnace firetube type boilers.
2) These BFG fired boilers need support of costly fuels in the form of either natural gas or petroleum oil to sustain the BFG flame.
3) The requirement of support fuel is typically upto 30% or even higher of the total heat input required for the boiler doe achieving required output capacity.
Taking into consideration the known BFG fired boilers, following are the disadvantages-
1) BFG being a lean burning gas and due to peculiar construction of the furnace of these boilers, in many cases costly support fuel in the form of oil or natural gas is continuously required to be burnt to sustain the flame of BFG.
2) Due to peculiar construction of these boilers and BFG being a lean burning gas, during every restart, the boiler needs to be started under all circumstances with supporting fuel till the boiler furnace conditions is stabilized and the furnace achieves the temperature of typically 700 Deg. C or higher. The time required for stabilizing furnace conditions is very high which demands very high consumption of costly support fuel.
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3) In case of BFG fired watertube boilers which are essentially field erected, initial cost is very high as compared to the invention mentioned herein below. Hence many projects find investment in watertube boilers much less attractive compared to invention mentioned herein below. Due to this, BFG is even flared and burnt without use resulting in wastage of energy which is national loss.
4) The requirement of costly support fuel increases the running cost of the boiler, as the cost of oil / natural gas is substantially higher compared to BFG. Even if BFG is available with the user in sufficient quantity and at low cost, the same can not be fully utilized without continuous consumption of costly fuel.
5) Since the BFG can not be stored in large quantities, the excess BFG has to be flared and burnt in the atmosphere thereby resulting in substantial or nearly total loss of heat. This results on one side in colossal wastage of energy and on other side colossal consumption of costly petroleum fuels which is a national loss.
6) Additional investment in the form of support fuel burner, the fuel handling, storage and preparation is required. This further increases overall investment cost and weakens techno-economic feasibility.
7) Furnaces of watertube boilers not having membrane panel in the furnace are not water tight, hence in case of even minor leakage from the furnace of the BFG fired boiler, there exists fire, explosion hazards as well as health hazard due to leakage of unbumt BFG in the atmosphere. BFG contains poisonous Carbon Monoxide as a constituent in its components.
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8) The conventional BFG fired boilers do not have heat recovery units and are hence less efficient.
9) Furnace volume of "internal water cooled furnace" type firetube boilers is very much inadequate and hence continuous burning of substantial quantity of support fuel becomes a must for reliable continuous operation of BFG fired boiler.
10) There are severe capacities and output limitations on "internal furnace" type firetube boilers. Hence a battery having multiple boilers is needed to meet the requirements. This results in high initial cost as well as high operation and maintenance cost. Manpower needed to monitor boiler house is also much higher.
PRESENT SECNARIO AND NEED OF THE PRESENT INVENTION:
1) Blast furnace gas (BFG) is byproduct of iron making process. It is the gas discharged from the steel mill blast furnace. It contains typically about 25% by volume poisonous and toxic Carbon Monoxide (CO). Its heating value is in the range of 600-700 kcal/Nm . Typical composition and its range is shown in Table I.
2) Conventionally in steel industries, the present design of available boilers has limitations mentioned here in above and here in below.
3) Since BFG has less calorific value it was not considered as a sole source of energy.
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4) Since support fuel is continuously used, whole amount of BFG is not utilized. Since the excess BFG can not be stored in large quantities; it has to be flared in the atmosphere without utilizing the heat content in the gas. This excess BFG can be utilized effectively if only BFG is used as fuel for steam generation, reducing the use of costly petroleum fuel.
5) If the boiler is used intermittently, at every start due to peculiar construction of the boiler, costly supporting fuel has to be used to attain steady state condition in combustion chamber. Thus in such case, the BFG can not be utilized effectively which results in increase of operating cost of the plant due to increase in use of costly supporting fuel.
6) Cost of conventional fuels like oil or natural gas has gone high and continues to rise at alarming rate. These fossil fuels are not environment friendly. Hence industries are searching for cheaper source of energy.
7) Since BFG is gas discharged from steel mill blast furnace, it is available readily at very low cost or no cost
8) Table 2 describes the savings possible if only BFG is used as fuel.
It is therefore the objective of the new invention to develop a novel design which will eliminate above limitations and all BFG producing process and users can get benefited from the new design.
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Table 1
Typical composition of Blast Furnace Gas (BFG)
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Table 2. Typical savings possible with the use of newly invented Blast Furnace Gas (BFG) fired boiler

No. Key Parameters Unit Existing Design New invention
FOas support fuel LDO as support fuel HSD as support fuel NGas support fuel operated on 100 % BFG
1 Steam Generation capacity considered for comparison Metric Tons/hr from & at 100 DegC 10 10 10 10 10
2 Boiler heat input at 85% efficiency kcal/hr 6352941 6352941 6352941 6352941 6352941
3 Percentage of heat supplied by support fuel % 30 30 30 30 Nil
4 Heat given by support fuel kcal/hr 1905882 1905882 1905882 1905882 Negligible
5 Heat given by BFG kcal/hr 4447059 4447059 4447059 4447059 6352941
6 Calorific Value of support fuel Kcal/kg 9710 10210 10280 11400 NA
7 Calorific Value of BFG Kcal/kg 465 465 465 465 465
8 Typical amount of support fuel required Kg/hr 196 187 185 167 Nil
9 Amount of BFG required Kg/hr 9564 9564 9564 9564 13662
10 Amount of support fuel required per annum (based on 7000 hrs of working) Kg 1373963 1306677 1297780 1170279 Nil
11 Amount of BFG required per annum (based on 7000 hrs of working) Kg 66944972 66944972 66944972 66944972 95635674
12 Cost of fuel Rs/kg 14 21 33 9 Nil
13 Fuel cost per annum Rs./year 19235476 27440226 42826734 9947368 Nil
14 Fuel cost saved due to new Design Rs./year w.r.t. FO as fuel w.r.t. LDO as fuel w.r.t. HSD as fuel w.r.t. NG as fuel 1923547627440226428267349947368

Assumption: BFG is available as byproduct of steel mill and it is free of cost.
FO: Furnace Oil; LDO: Light Diesel Oil; HSD: High Speed Diesel; NG: Natural Gas

SUMMARY OF THE INVENTION:
The present invention aims to provide a high efficiency compact BFG fired steam boiler.
It is also the object of the present invention to provide the BFG fired boiler, which does not, require any support fuel except during cold start conditions which are very occasional. (Typically once or twice a year)
It is also the object of the present invention to overcome and eliminate the drawbacks and shortfalls of the prior art.
In the boiler of the present invention BFG is burnt in a separate combustion air cooled air tight steel sheet enclosed cylindrical refractory lined combustion chamber. The air required for combustion of BFG is supplied by a forced draft fan. A separate dilution air fan is also provided to maintain the flue gas temperature typically in the range of 1000 to 1200 Deg. C. This is done to protect certain types of refractory from getting overheated beyond its acceptable value. This temperature can be adjusted from design to design depending upon refractory material selected from those available. The flue gases are passed through a fire tube boiler and steam is generated. The flue gases leaving the boiler which are typically at a temperature of 300 to 400 Deg C are passed through an economizer where feed water is preheated typically from 90 Deg C upto saturation temperature at steam pressure. A steam superheater can also be provided as an optional device between boiler and economizer to suit the specific requirement. The combustion chamber, during use is continuously maintained under slightly negative pressure by an induced draft fan. The steam generation and steam pressure is controlled through a step less modulating control system. The flow of BFG into the combustion chamber is controlled through a gas train with all the necessary safeties and interlocks. A pilot gas or oil burner is provided only for the purpose of cold start of the boiler. The provision can

also be made to operate the boiler folly or partially on oil or natural gas as stand-by fuels when BFG is not available fully or partially.
BRIEF DESCRIPTION OF SCHEMATIC DRAWING:
The invention is described with respect to accompanying Figure 1; having simplified flow diagram of newly invented high efficiency blast furnace gas fired steam boiler.
DETAILED DESCRD7TION OF THE SCHEMATIC DRAWING:
Referring to accompanying Figure 1, following components can be identified in the system.
1) BFG gas train
2) Combustion chamber
3) BFG burner
4) Pilot fuel burner
5) Smoke tube type evaporator
6) Economizer
7) Induced draft fan
8) Combustion air fan
9) Dilution air fan
10) Superheater (Optional)
Blast furnace gas produced in the blast furnace enters the BFG gas train (marked as item no.l) after getting properly cleaned. The flow of BFG into the combustion chamber (marked as item no. 2) is controlled through the said gas train at steady automatically regulated preset pressure with all the necessary safeties and interlocks. Preset BFG pressure can be adjusted to suit the gas composition and desired firing condition and objectives. The said BFG gas train consists of water seal, pressure indicator and control valves. Water seal prevents the entry of BFG to the BFG furnace during shut down of
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boiler. The controlled BFG flow then enters into the cylindrical shaped BFG combustion chamber (marked as item no.2). BFG burners (marked as item no.3) are provided on front side of combustion chamber in required and suitable numbers depending on needed firing rate and boiler capacity. These burners are arranged radially on the front wall of the said combustion chamber and pilot oil/gas burner (marked as item no.4) is provided at the centre. The said pilot burner is provided for the purpose of cold starting of the boiler. When the temperature in combustion chamber is reached beyond auto ignition temperature of BFG, the steady state in combustion chamber gets achieved. Once the steady state is achieved in boiler, the supply of support fuel to pilot burner is cut off. Now the flame is sustained with use of BFG only. Combustion air is supplied into the said combustion chamber with the help of combustion air fan (marked as item no.8). This combustion air is preheated by circulating it around the refractory lined combustion chamber. This preheated air not only provides effective cooling to refractory but it also assists the combustion of BFG in the said combustion chamber. Required dilution air supplied by dilution air fan (marked as item no.9) maintains the temperature of the said combustion chamber typically in the range of about 1100 to 1200 Deg C. The said combustion chamber is lined with refractory material. Refractory lined combustion chamber provides high thermal inertia which maintains the temperature of chamber above the auto ignition temperature of BFG. Thus only BFG can be used as a fuel to operate the combustion chamber. The thermal inertia provided by hot refractory is adequate for various firing rates that prevail at different steam generation rates depending on steam demands.
The said BFG burners are placed at front end of combustion chamber. Each burner is of air staged axial swirl type. Burner consists of three concentric pipe sections. At front end of each stage i.e. pipe section, axial swirler fan is provided. Innermost pipe provided for air stage out of three concentric pipe sections provides path for primary air. Outermost sections provides path for secondary air. Middle section carries BFG. Blade orientation of
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primary and secondary air is kept in same direction. Orientation of blades of BFG is kept in opposite direction with respect to that of primary and secondary air. Such type of arrangement creates enough intense turbulence for proper mixing of BFG and both stages of combustion air. The vanes for secondary air (outer stage) are designed for higher velocity. Due to this, the secondary air travels more distance in furnace. This assures the complete combustion of BFG. At the rear end of burner, suitable sizes of inlet nozzles are provided for primary air inlet and BFG inlet supply to burner. Secondary air directly passes from refractory shell to passage of secondary air (outer stage).
The flue gases, generated by burning BFG are passed through a smoke tube evaporator (marked as item no.5) and steam is generated on shell side. The smoke tube evaporator is provided with the ferrules made of refractory materials to protect the tube to tube sheet welding joints from over heating due to hot gases entering into the furnace if any abnormal condition arises.
The flue gases leaving the evaporator typically at a temperature of 300 to 400 Deg C are passed through an economizer (marked as item no .6) where feed water is preheated typically from 90 Deg C upto saturation temperature. A superheater (marked as item no. 10) can also be provided as an optional device between boiler and economizer to suit the specific requirement.
Different interlocks and control valves are provided in the system for safety and reliability. Combustion chamber pressure is continuously and automatically maintained at set negative pressure through continuous modulation control system using pressure transmitter and PID controller, motorized air damper provided at suitable location in air and flue gas ducting respectively, frequency inverter driven forced draft and induced draft fans. The steam generation and steam pressure is controlled through a step less modulating control system using steam pressure transmitter and control valves to
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modulate burner firing rate and combustion air flow rate. The flow of dilution air is controlled continuously and automatically with the help of temperature indicator, PID and motorized damper. All these controls are properly interlocked for correct proportions of BFG and combustion air. Refer typical P & I diagram attached. The said BFG gas train is provided with water seal at the entry which controls BFG flow rate to the combustion chamber. The said smoke tube type evaporator is provided with level indicator, level transmitter, safety valve, and blow down valve.
Following advantages are achieved by the present invention
1) Refractory lined combustion chamber provides high thermal inertia. Hence no supporting fuel is required to be burnt once the boiler achieves steady state of operation and the flame can be sustained with only BFG as fuel.
2) Supporting fuel is required only during cold start, which can be achieved by a pilot burner.
3) Due to high thermal inertia of refractory^ there is no requirement of support fuel even during automatic cut-in and cut-off operation of the boiler during partial low load conditions.
4) The running cost of the boiler is reduced substantially as there is no requirement of costly support fuel.
5) The BFG, if available in sufficient quantities, it can be completely utilized and no flaring in atmosphere is required. This not only reduces the running cost of the user but also reduces emission of green house gases and earns national wealth.
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6) The combustion air required for combustion of BFG is circulated over the refractory lined combustion chamber before it enters the combustion chamber. This air not only provides effective cooling to the refractory, thereby improving its life, but also provides pre-heated combustion air for BFG to assist combustion and improves combustion efficiency as well as reliability.
7) The smoke tube evaporator is provided with the ferrules made of refractory materials to protect the tube to tube sheet welding joints from over heating due to hot gases entering into the furnace.
8) Due to balanced draft system and sheet metal enclosure to combustion chamber, the entire combustion chamber is maintained reliably under slightly negative pressure and hence there is no possibility of leakage of carbon monoxide (CO) into the atmosphere during operation of the boiler.
9) Due to sheet metal enclosure of combustion chamber and due to circulation of combustion air around the refractory lined combustion chamber, BFG does not leak anytime and any operating condition into the atmosphere. Since combustion air jacket on refractory lined combustion chamber is under higher air pressure than combustion chamber, air injected will enter the combustion chamber but will not allow BFG to escape to the atmosphere even a crack or pinhole develops on combustion chamber on prolonged use.
10) With economizer as a heat recovery unit, the thermal efficiency of the boiler can be as high as 88% + 2% on net calorific value of fuel.
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11) To suit the specific requirement, the pilot burner can be designed to generate the full rated capacity of the boiler, when BFG is not available as fuel i.e. the same burner can act as support burner as well as standby burner.
12) The dilution air fan is provided to restrict the flue gas temperature typically in the range of 1000 to 1200 Deg. C to protect the tube to tube sheet welding joints of the main evaporator from over heating. This temperature after dilution can be adjusted and is controlled automatically and continuously through the use of PID and motorized dampen
13) Large number of safeties and interlocks are provided to ensure safe, reliable and automatic operation of the boiler.
VARIATIONS POSSIBLE TO BE COVERED AND PROVIDED WITHIN THE INVENTION OF HIGH EFFICIENCY COMPACT BLAST FURNACE GAS FIRED STEAM BOILERS:
1. Various forms of heat output i.e. steam generation, Thermic fluid/hot oil generator, hot water generator, air/gas preheating, hot air generation etc.
2. Various steam generation heat generation capacities and outputs
3. Various working steam pressures
4. Various steam superheat temperatures
5. Various outlet temperatures of Thermic fluids, hot water hot air etc.
6. Various compositions of BFG and calorific values of BFG
7. Various refractory materials
8. Various types of heat exchangers/heat generators at outlet of BFG furnace viz. smoke tube type, coil type, watertube type, etc for different applications like steam generation, Thermic fluid/hot oil generator, hot water generator, air/gas preheating, hot air generation etc.
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Claims:
1) High efficiency fiilly automatic safe and reliable compact blast fiimace gas fired steam boiler comprising of refractoiy lined combustion chamber for combustion of BFG with air staged axial swirl type BFG burners provided for burning of BFG at front end; smoke tube type evaporator provided for steam generation installed at the exit of combustion chamber; pilot fuel burner provided at front end of combustion chamber for cold start of BFG combustion chamber which can act as stand by burner as well; the balanced draft system comprising of forced draft fan, dilution air fan, induced draft fan, gas ducting and draft control system; gas train provided for regulations and modulation of blast furnace gas flow and pressure into the combustion chamber; instruments, controls and safeties for automatic and reliable operation of the boiler.
2) High efficiency fully automatic safe and reliable compact blast fiimace gas fired steam boiler as claimed in claim no. 1 wherein only BFG is used for steam generation.
3) High efficiency fiilly automatic safe and reliable compact blast fiimace gas fired steam boiler as claimed in claims no. 1 & 2 wherein, refractory lined combustion chamber is provided in which temperature is maintained above auto ignition temperature of BFG.
4) High efficiency fiilly automatic safe and reliable compact blast furnace gas fired steam boiler as claimed in claims no. 1, 2, & 3 wherein smoke tube type evaporator is used for steam generation.
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5) High efficiency fully automatic safe and reliable compact blast furnace gas fired steam boiler as claimed in claims no. 1, 2, 3 & 4 wherein the smoke tube evaporator is provided with the ferrules made of refractory materials.
6) High efficiency fully automatic safe and reliable compact blast furnace gas fired steam boiler as claimed in claims no. 1,2, 3,4 & 5 wherein air staged axial swirl type burner provided for burning BFG has three different paths for primary air, secondary air and BFG.
7) High efficiency fully automatic safe and reliable compact blast furnace gas fired steam boiler as claimed in claims no. 1, 2, 3,4, 5 & 6 wherein, combustion air is preheated around the shell of refractory lined BFG combustion chamber before entering BFG burner.
8) High efficiency fully automatic safe and reliable compact blast furnace gas fired steam boiler as claimed in claims no. 1, 2, 3,4, 5, 6 & 7 wherein, dilution air is supplied for maintaining the temperature of BFG furnace under safe limit.
9) High efficiency fully automatic safe and reliable compact blast furnace gas fired steam boiler as claimed in claims no. 1, 2, 3, 4, 5, 6 7, & 8 wherein, smoke tube type evaporator is provided with level indicator, level transmitter, safety valve, blow down valve.
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10) High efficiency folly automatic safe and reliable blast fomace gas fired steam boiler as claimed in claims no. 1, 2, 3, 4, 5, 6, 7, 8, & 9 above and herein described with respect to accompanying Figure no. 1.
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ABSTRACT
High efficiency fully automatic safe and reliable compact blast furnace gas fired steam boiler comprising of refractory lined combustion chamber for combustion of BFG with air staged axial swirl type BFG burners provided for burning of BFG at front end; smoke tube type evaporator provided for steam generation installed at the exit of combustion chamber; pilot fuel burner provided at front end of combustion chamber for cold start of BFG combustion chamber which can act as stand by burner as well; the balanced draft system comprising of forced draft fan, dilution air fan, induced draft fan, gas ducting and draft control system; gas train provided for regulations and modulation of blast furnace gas flow and pressure into the combustion chamber; instruments, controls and safeties for automatic and reliable operation of the boiler.
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A SYSTEM FOR WASTE HEAT DRIVEN COMBUSTION TURBINE INLET AIR COOLING

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