FIELD OF THE INVENTION
The present invention relates to a process for the recovery of sulphur from an acid gas in a Claus type sulphur plant. The invention in particular relates to the removal of sulphur species namely hydrogen sulphide, carbonyl sulphide and carbon disulphide from acid gas through an oxygen enrichment process. The invention also relates to a process for capacity enhancement of Claus type sulphur plant by 15% - 30% using oxygen enriched air. The invention further relates to a device meant for uniform mixing of combustion air with oxygen.
BACKGROUND OF THE INVENTION
The recovery of elementary sulphur from hydrogen sulfide (H2S) containing gas streams is known in the art as disclosed in the article "Fundamental of Sulphur Recovery by the Claus Process" by B. Gene Goar published in the 1977 Gas Conference Report. The conventional thermal and catalytic Claus process is widely practiced and accounts for a major portion of total production of sulphur. In a Claus sulphur recovery plant (SRU), the first step is thermal oxidation of a fraction of H2S in the acid gas feed to SO2. This typically carried out in the thermal reaction zone (Claus furnace) by the addition of air to acid gas which contains mainly H2S but may contain CO2 and possibly hydrocarbons. In the oxidation step, in addition to SO2, the products also include elementary sulphur and water. The down stream catalytic reactors have effective Claus catalyst. The conversion achieved in each reactor is equilibrium limited. Typically reactions occurred in such Claus plant can be summarized by the following equations
H2S + 3/2 O2 H2O + SO2 (Oxidation)
2H2S + SO2 2 H2O + 3 S (Claus reaction)
H2S +1/2 O2 H2O + S (Overall)
The use of air as the source of elementary or free oxygen in the thermal reactor introduces large quantity of N2 in to the process. Equipment must be sized into handle this volume of inert gas. By increasing the concentration of O2 in the oxygen source, the quantity of N2, which must be processed, can be reduced. Such oxygen enrichment can significantly increase the capacity of an existing Claus plant and or reduce the capital investment for a new plant.
Oxygen enrichment in the operation of a Claus sulphur plant to increase the capacity of H2S treated in such a plant has also been disclosed in the article 'Oxygen Use in Claus Sulphur Plants' by M.R.Gray and W.Y.Svreck, published in the 1981 Gas Conditioning Conference Report. It was disclosed more specifically that oxygen can be added to the air feed to the burner of a reaction furnace in a Claus Sulphur plant to increase the amount of H2S which is combusted to sulphur dioxide for later catalytic conversion to elementary liquids sulphur product. The maximum capacity increase which can be achieved with oxygen enrichment is determined by the pressure drop through the plant, the reactor space velocity and the temperature of the reaction furnace and the various catalytic zones, particularly the refractory materials used in the furnace of the Claus plant.
In the 1983 publication by Linde of Union Carbide entitled "Claus Plant Oxygen Enrichment", it is noted that oxygen -enrichment limits exist for rich hydrogen sulfide streams due to temperature limits in the furnace or waste heat boiler of the Claus plant.
US 4481181 discloses a Claus plant, which uses oxygen enrichment. A process is provided for recovery of H2 from H2S utilizing the partial combustion of H2S with oxygen to produce sufficient heat to effect thermal decomposition of a substantial portion of the unoxidised H2S. H2S is introduced along with oxygen into a reaction zone in a molar or volume ratio of greater than 10:1. The exothermic combustion reaction, which yields sulphur and water, is used to affect the final raise in temperature and to maintain the temperature within reaction zone above 1027 °C. Promptly quenching the mixture with cooler gas instantaneously reduces the temperature of the gas to below 927 °C and effectively blocks any significant recombination of elementary sulphur. It would otherwise occur in the time usually required to operate even a fast heat exchanger. The available heat in the gases, which result from quenching, is used to raise the temperature of the incoming stream to about 827 °C.
US 4279882 discloses a Claus plant using oxygen enrichment. According to the invention, there is provided a novel Claus process which eliminates the thermal reactor, including its combustion chamber and heat exchanger, and which is applicable to the treatment of gas streams containing from about 1 to 100 % by volume of H2S. The process is particularly suited to small plants having output of 20 tones per day of sulphur or less. A stoichiometric amount of oxygen is preferably employed in the mixture of H2S and oxygen. H2S is catalytically converted to SO2 and sulphur at a temperature of 370 °C.
US 3822341 discloses a Claus plant, which uses oxygen enrichment. The process involves reacting oxygen and H2S with cooling so that the effluent is at temperature between 315 ° C to 400 ° C. Those reaction gases are then reacted in a Claus reactor. Liquid sulphur is removed from the gases by lowering the temperature of the gases in a condenser.
US 4279882 discloses a sulphur recovery process, which uses only a series of catalytic reaction beds rather than a reaction furnace, as in the traditional Claus plant. A temperature modifying recycle stream is set forth in the patent, wherein a stream is returned to the feed in order to control the temperature in the catalytic zones. This process is economical only for dilute H2S feed gas specifications. It requires a recycle blower operating at high temperature. US 4632818 and EP 0220619 Bl disclose a process from recovery of sulphur from H2S containing gas using oxygen-enriched air in a Claus reaction furnace. The process is directed to an improved method of the temperature moderation in the reaction furnace (538 °C to 927 °C) by introducing elementary sulphur into the Claus reaction zone as a temperature moderator or reaction effluent quench. The process is relevant for feed gas H2S contents of 60 %v or more. Preferably, H2S to O2 ratio is -2.5 : 1 but would decrease if the feed gas contains hydrocarbons. Preferable combustion zone temperature is 1316 °C while the combustion zone effluent is quenched to 760 °C by injecting liquid sulphur (17 g/gm mole of effluent)
US 4756900 discloses a Claus plant, which uses oxygen enrichment. In the process, the combustion effluent from a waste heat boiler is divided into a first and second streams so that the sulphur in the first stream is condensed and then the stream is passed on to later Claus reaction stages. Sulphur in the second stream is condensed and then this stream is introduced in the Claus reaction furnace to moderate the temperature. The temperature of the effluent of the second condensation zone is 115 °C - 148 °C.
U.S. Patent 4798716 discloses a Claus plant, which uses oxygen enrichment. In the process, the temperature of the Claus reaction furnace is moderated by returning a portion of the dried condenser effluent as diluents to combustion chamber of the reaction furnace. The process uses either pure oxygen or oxygen enriched air in the reaction furnace.
U.S. Patent 4138473 discloses a Claus plant, which uses pure oxygen. In this process, the gaseous output of the final converter is combusted with oxygen in a final catalytic converter
to convert any remaining H2S to SO2. The H2O, SO2 and CO2 mixture emerging from the converter is treated to remove H2O and CO2. A concentrated SO2 is returned the Claus furnace. This process requires a large amount of water to absorb SO2 and also requires heat inputs in the stripping of SO2 from the aqueous solution.
In view of all the drawbacks of the prior art processes for the recovery of elementary sulphur, there is still need to develop a process and an apparatus for an efficient recovery of sulphur from a gas stream containing hydrogen sulphide.
OBJECTS OF THE INVENTION
The principal object of the present invention is to recover elementary sulphur from acid gas in a Claus type sulphur plant using oxygen-enriched air.
Another object of the invention is to increase the processing capacity of the plant.
Another object is to provide a mixing device for complete mixing of oxygen with plant/combustion air.
Still another object of the invention to provide a process for complete destruction of ammonia in the feed gas (acid gas).
It is a further object of the invention to provide a low cost process for smooth operation of the sulphur plant by reducing the backpressure of the plant by minimizing inert gas quantity in the process gas stream.
SUMMARY OF THE INVENTION
The present invention provides a process for the recovery of elementary sulphur from acid gas through oxygen enrichment process. Said process involves removal of hydrogen sulphide (H2S), carbonyl sulphide, and carbon disulfide from amine regenerator off gas called as acid gas in Claus type sulphur plants by using air with high oxygen concentration. The Claus type sulphur plant comprises main burner, main combustion chamber, and Claus reactors/converters, heat recovery facilities like waste heat boiler and condensers, and incinerator for processing of acid gas and sour water stripper gases.
In one embodiment the Claus type sulphur plants is provided with an oxygen mixing device for enrichment of combustion air with oxygen.
In another embodiment the Claus type sulphur plant is also provided with an oxygen analyser for controlling the oxygen concentration in the combustion air.
In another embodiment the capacity of Claus sulphur plant is increased by 15% - 30% using oxygen enriched combustion air.
In another embodiment oxygen concentration in the combustion air is maintained in the range of 23- 30%.
In another embodiment of the invention said oxygen mixing device has a manifold design and comprises air blower discharge pipe, body flange, oxygen manifold shell, oxygen manifold plate, oxygen pipe, oxygen inlet flange, nozzles and supporting plate.
In still another embodiment, said mixing device consists of four circumferentially placed nozzles, directing the flow towards the center of the main pipe and oriented at an angel ranging from 30 ° to 45° preferably at 45° angle
In yet another embodiment of the invention, nozzles in the mixing device are projected inside the main air pipe through circular or rectangular slots. In the preferred embodiment said nozzles have circular slots.
In yet another embodiment of the invention, uniform mass flow distribution of oxygen to these nozzles is achieved through a manifold placed around the main air pipe.
In another embodiment of the invention, pressure drop in oxygen line is in the range of 50 to 80 mbar and mass fraction deviation of the range of 2.0% to 2.7%.
In another embodiment of the invention, complete mixing of combustion air and oxygen is achieved over a length equal to five to seven times of the main pipe from the point of injection of oxygen into the main air pipe.
In another embodiment of the invention, the temperature of the process gas in the main combustion chamber of the plant is increased to 1300-1500 ° C.
In another embodiment of the invention, complete destruction of ammonia and combustion hydrocarbons are done in the main burner of the plant.
In another embodiment backpressure in the plant is reduced due to less nitrogen in the process gas that gives smooth and trouble free operation of the plant.
In another embodiment of the invention, stable flame in main burner of the plant is achieved even at H2S concentration of the feed acid gas less than 50%.
In another embodiment of the invention, implementation of process for running Claus type sulphur plant takes minimum modification and minimum shutdown period.
In another embodiment of the invention, flexibility in Claus type sulphur recovery plant operation by using either oxygen-enriched air or normal air is maintained.
In another embodiment the back pressure of the plant drops by -0.1 Kg/cm2
BRIEF DESCRIPTION OF DRAWINGS
The above and other aspects and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments, taken in conjunction with the drawing, wherein:
Figure 1 is a schematic representation of the oxygen mixing device and Claus type sulphur
plant.
Figure 2 is a schematic representation of front view of oxygen mixing device
Figure 3 is a schematic representation of top view of oxygen mixing device and cross
sectional view of nozzle.
Figure 4 provides graphical representation of the contours of the velocity profile and oxygen
concentration in the combustion airflow on three planes till x = 2.5 meter.
Figure 5 provides graphical representation of contours of mass fraction of oxygen on three planes till x = 2.5 meter.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a process for the recovery of elementary sulphur from acid gas through oxygen enrichment process. The acid gas herein means a gas coming out of Amine regenerator and comprises a mixture of hydrogen sulphide, H2O, H2, NH3, hydrocarbons having C1-C4 carbon species and sometimes CO2.
The present invention overcomes the shortcoming of the prior art by increasing throughput of Claus plant with oxygen enrichment beyond the known feasible limits of the prior art. The invention provides better throughput of reaction components in the Claus type sulphur plant by reducing nitrogen in process gas. This is achieved by proper mixing of oxygen with air in advance to entry of oxygen-enriched air to main burner of the Claus burner. A mixing devise dedicated for mixing of oxygen with air in a short distance ensures stable and controlled flame in the Claus burner and better control on the main combustion chamber effluent temperature.
The process according to the present invention will now be described in more detail with reference to the accompanying Figures 1-5.
The process and the oxygen mixing device are demonstrated in a commercial Claus type sulphur plant (SRU) as shown in Figure 1. The plant comprises main burner(115), main combustion chamber (116), four Claus reactors/converters (120,123,125,127), heat recovery facilities like waste heat boiler (117) and condensers (118,122,124,126,128), gas-gas exchanger (121) and incinerator (129). The last three Claus reactors/converters are operated at low temperature.
Oxygen supply to the plant is carried out by using liquid oxygen vaporizer (113). Injection of oxygen to the combustion air coming from the air blower (112) is done using an oxygen-mixing device (114). The oxygen-mixing device is installed in the combustion air pipe. It has a manifold design.
The oxygen mixing device (114) comprises air blower discharge pipe (211) for the flow of air from air blower. Said Manifold is kept in place with main air pipe through a body flange (212). The device has oxygen manifold shell (213) for the uniform distribution of oxygen in the air passing through the main pipe. Oxygen manifold is provided with oxygen manifold plate (214). Oxygen to the manifold is entered through an oxygen pipe (215). Further oxygen inlet flanges are present for the support of said manifold. The device has tapered nozzles (217) having circular or rectangular slots. The nozzles are oriented at an angle of 30 ° -45° along the circumference of the combustion air pipe. The device has supporting plate (218). The front view and top view of the oxygen mixing device; and cross-section view of nozzle are shown in Figures 2 and 3.
The concentration of oxygen in the combustion air is maintained in the range of 23-30%. For controlling the oxygen flow, an online oxygen analyzer is provided in the combustion air pipe.
Based on computational fluid dynamic study for design of the manifold, estimated distance equivalent for complete mixing of oxygen with air is around 7 times of the combustion air pipe diameter and the deviation in oxygen concentration across the cross section of flow of oxygen enriched air is ± 3%. Figures 4 and 5 provide the contours of the velocity profile and oxygen concentration in the combustion airflow.
The acid gas is fed to the main burner through a source (111). This acid gas is rich in sulphur species and contains more than 90% hydrogen sulphide (H2S). The main burner(115) provides complete mixing of air or oxygen enriched air with acid gas for oxidation of all hydrocarbons, residual sulphur compounds, ammonia and one third of the total hydrogen sulphide present in acid gas. Also there is a complete destruction of ammonia (NH3) and improved combustion of hydrocarbons present in acid gas and sour water stripper gas in oxygen-enriched environment in main burner of the plant.
In the main burner (115) and main combustion chamber (116), one third of the hydrogen sulfide in the acid stream is burnt to form sulphur dioxide (SO2). The resulting sulphur dioxide is then reacted with the balance of H2S to form elementary sulphur (S) and water in vapor phase in the first Claus reactor/converter and subsequently in the Claus reactors operated at low temperature.
The Claus reaction started in the main combustion chamber (116). The temperature of main combustion chamber temperature is between 1300-1500°C. The hot process gas is cooled in a waste heat boiler (117) and subsequently sulphur is removed as liquid sulphur from the sulphur condenser(l 18). The cold process gas is heated in reheater (119) and passed through Claus reactors/converters (120,123,125,127), gas-gas exchanger (121) and condensers (122,124,126,128) in the downstream of the first condenser. The last three Claus reactors/converters are operated at low temperature.
The process gas from the end condenser (128) is passed to incinerator (129) for burning the unreacted hydrogen sulphide and other sulphur species in the acid gas to sulphur dioxide and discharging tail gas to the atmosphere.
The process disclosed in the present invention provides a trouble free operation. Oxygen enrichment makes the operation smooth and trouble free by providing less pressure drop in the plant and stable flame in the main burner. Injection of oxygen in combustion air line instantaneously reduces backpressure and high temperature in main combustion chamber. The back pressure of the plant drops by -0.1 Kg/cm2.
The process disclosed in the present invention also provides a quick change over from air mode operation to oxygen enriched mode operation. Sometimes the process encounters low acid gas flow. Continuation of operation is done immediately by switching over from oxygen enrichment operation to normal operation with plant air. Oxygen supply is stopped and airflow is adjusted based on acid gas flow and its' composition. Change of operation mode does not call for any precautionary steps neither for main burner and main combustion chamber nor the down stream equipments of main combustion chamber.
A stable flame and good color flame is observed in main burner even at lean acid gas flow. Relatively less nitrogen in combustion air is the reason for good flame stability and high temperature is the reason for greenish color of the flame.
The prior art plants are prone to backpressure problem and due to which it is difficult to increase acid gas flow to the plant beyond certain limits. In the present invention increased oxygen concentration in combustion air increases the acid gas flow by reducing backpressure in the plant.
In the present process a steep increase in main combustion chamber temperature is observed. The total steam production from waste heat boilers and other condensers is increased due to processing of more acid gas by the plant under oxygen enrichment condition.
In the present invention capacity of Claus sulphur plant is increased by 15% - 30% using oxygen enriched combustion air.
The present process provides improvement in sulphur recovery. High sulphur recovery is confirmed from SO2 and H2S level in flue gas.
Example:
The invention is now described by way of the following non-limiting example:
An existing commercial Claus plant of capacity 90 tones per day is revamped for testing the process and the device. The oxygen-mixing device is installed in the combustion air pipe. It is a manifold design with four circular tapered nozzles. The nozzles are oriented at an angle of 45° along the circumference of the combustion air pipe. Oxygen is injected gradually to the combustion air through oxygen mixing device and the airflow is reduced keeping the total moles of oxygen in oxygen-enriched air at desired level. Initially, the concentration of oxygen in the combustion air is maintained at 23.9%v by injecting oxygen in the combustion air and the backpressure of the train is reduced to 0.6 Kg/cm2 from 0.7 Kg/cm2 The system parameters like main combustion temperature, backpressure, Claus Converter temperatures etc. are checked continuously during test run.
The acid gas flow is further increased by 26.8% by increasing oxygen concentration. Table 1 shows the increase in capacity of plant after test run. Results show increase in steam flow for this process and reduction in air flow.
The oxygen concentration in the oxygen-enriched air is adjusted to 27.3 %v during test run but the plant is able to get more oxygen concentration. The temperature of main combustion chamber temperature is 1466°C. It is observed that the temperature of main combustion chamber temperature is increased with increase in oxygen concentration. Table 2 shows the increase in process gas temperature at different oxygen concentration.
Increase in oxygen concentration of the oxygen-enriched air shows instantaneous reduction in the back pressure when the same acid gas flow is maintained in the plant. This is due to less nitrogen in the combustion air. Table 3 shows the reduction in backpressure in the plant at different oxygen concentration.
The process gas from main combustion chamber is cooled in the waste heat boiler and first condenser. The process gas is heated in the line burner before passing the gas to first converter. The bed temperature of Claus converter changes from 290°C to 326°C an indicator of the better conversions of H2S and SO2 to sulphur.
The last three Claus reactors/converters are operated at low temperature. The overall sulphur recovery of the plant is more than 99%. The sulphur recovery is improved due to conversion of H2S to sulphur in main combustion chamber at high temperature.
Overall operation during oxygen injection is found smooth and trouble free. Stable flame in main burner, less back pressure, more sulphur formation in main combustion chamber are few factors for better operation.
The laboratory analysis is carried out for analysis of feed acid gas, tail gas, enriched air and stack gas to regulate the operation. The concentration of H2S in the feed acid is found more than 90%v during test run in most of the time.
The process and apparatus disclosed in the present invention provides following advantages:
• Trouble free operation: Oxygen enrichment makes the operation smooth and trouble free by providing less pressure drop and stable flame in main burner. Injection of oxygen in combustion air line instantaneously reduces backpressure and high temperature in main combustion chamber.
• Quick change over from air mode operation to oxygen enriched mode operation: The process encounters low acid gas flow for number of times. Continuation of operation is done by immediate switching over from oxygen enrichment operation to normal operation with plant air. Oxygen supply is stopped and airflow is adjusted based on acid gas flow and its' composition. Change of operation mode does not require
additional precautionary steps neither for main burner/main combustion chamber nor the down stream equipments of main combustion chamber.
• Stable flame in Main Burner: The invention provides a very stable and good color of the flame even at lean acid gas flow due to lesser percentage of nitrogen in the combustion air and high temperature.
• Backpressure reduction: Generally Claus type Sulphur plant is prone to backpressure problem and acid gas flow to the plant can not be increased beyond a certain limit. In the present process increase in the oxygen concentration results in the reduction of backpressure in the plant and thus increases flow of acid gas.
• Steep increase in main combustion chamber temperature: The temperature of the process gas from the main combustion chamber is increased with oxygen concentration in the oxygen enriched air as shown in Table 2.
• Increase in Steam Production: The total steam production from WHB and all other condensers increase due to processing of more acid gas by the plant under oxygen enrichment condition.
• The process results into higher sulphur recover (>99 %).
Table 1: Capacity increase before and after test run

(Table Removed)
Table 2: Oxygen concentration Vs Main Combustion Chamber Temperature

(Table Removed)
Table 3: Oxygen Concentration Vs Backpressure of the plant
(Table Removed)

We claim:
1. A process for the recovery of sulphur from acid gas in a Claus type plant comprising
steps of:
(a) forming a mixture of acid gas with oxygen enriched air;
(b) subjecting said mixture to high temperature to form a process gas wherein a part of sulphur compounds present in the process gas is converted to sulphur dioxide, and subsequently to suphur;
(c) subjecting the hot process gas from step (b) to cooling to recover sulphur in liquid form;
(d) reheating said cold gas from step (c) to convert unreacted sulphur source to sulphur and further cooling said gas to recover sulphur in liquid form.

2. A process as claimed in claim 1 wherein feed acid gas in Claus type plant is subjected to plurality of steps of conversion of sulphur species into sulphur and condensation to recover sulphur before released into the atmosphere as tail gas.
3. A process as claimed in claim 1 wherein in step (b) the temperature ranges from 1300-1500°C
4. A process as claimed in claim 3 wherein the temperature is 1466 °C.
5. A process as claimed in claim 1 wherein the compound sulphur is hydrogen sulphide.
6. A process as claimed in claim 1 wherein acid gas comprises hydrogen sulphide at a concentration of more than 90%.
7. A process claimed in claim 1 wherein in step (a) mixing of acid gas with oxygen is done using a mixing device.
8. A process as claimed in claim 7 wherein acid gas is uniformly mixed with oxygen such that deviation in oxygen concentration across the cross section of flow oxygen enriched air is ± 3%.
9. A process as claimed in any preceding claim wherein the capacity of Claus type sulphur plants is increased by 15%-30%.
10. A process as claimed in any preceding claims wherein concentration of oxygen in the oxygen enriched air is maintained in the range of 23-30%.
11. A process as claimed in claim 10 wherein concentration of oxygen in the oxygen enriched air is maintained by an oxygen analyzer.
12. A process as claimed in any preceding claim wherein said process is carried out in Claus type sulphur plant wherein said plant comprises oxygen mixing device for enriching the combustion air with oxygen, main burner for uniform mixing of acid gas with oxygen enriched air, main combustion chamber for conversion of a part of sulphur compounds present in the acid gas to sulphur dioxide and subsequently to sulphur, one or more converters/reactors for converting unreacted hydrogen sulphide to sulphur , waste heat boiler and one or more condensers for cooling of hot acid gas and recovery of sulphur, and incinerator for burning the unreacted hydrogen sulphide and other sulphur species in the acid gas to sulphur dioxide and discharging said gas (tail gas) to the atmosphere.
13. A process as claimed in claim 13 wherein the temperature of Claus converter change from 290°C to 326°C.
14. A process as claimed in any preceding claim wherein complete mixing of air with oxygen takes place in the mixing device placed at a distance equivalent to 7 times the diameter of the combustion pipe of the Claus type plant.
15. A process as claimed in any preceding claim wherein back pressure of the plant drops by-0.1 Kg/cm2.
16. A process as claimed in any preceding claim wherein plant operation in Claus type sulphur plant is switched between oxygen-enriched air and normal air.
17. A process as claimed in any preceding claim involves complete destruction of ammonia present in the feed acid gas.
18. An apparatus for the recovery of sulphur in a Claus type sulphur plant comprising a mixing device (114) means for enrichment of combustion air with oxygen; said mixing device being connected to air vaporizer (113) means for supply of pure oxygen, an air blower (112) means for the supply of air to mixing device and main burner (115) means for mixing of acid gas with oxygen enriched air; said main burner being connected to a source of acid gas (111) and main combustion chamber (116) means for conversion of a part of sulphur compounds present in the acid gas to sulphur dioxide and subsequently to sulphur at a high temperature; said main combustion chamber being connected to waste heat boiler (117) which in turn is connected to a condenser (118) means for cooling said hot gas to recover sulphur; said condenser being connected to reheater (119) means for heating of process gas; reheater being connected to a converter (120) means for the conversion of unreacted sulphur sources to sulphur; said converter being connected to gas-gas exchange (121) and condenser (122) means for cooling the processed gas from converter; said gas-gas exchanger being connected to a series of converters (123,125,127) and condensers (124,126,128) for conversion of sulphur sources to elemental sulphur and recovery of sulphur; end condenser (128) being connected to an incinerator (129)means for burning the unreacted sulphur sources in the acid gas to sulphur dioxide and discharging tail gas to the atmosphere.
19. A mixing device (114) as claimed in any preceding claims has a manifold design and comprises an air blower discharge pipe (211) means for the flow of air from air blower (112), a body flange (212) for holding the manifold with main air pipe, oxygen manifold shell(213) for distributing oxygen uniformly in the air passing through the main pipe, oxygen manifold plate (214) as a part of oxygen manifold, oxygen pipe(215) for entry of oxygen to the manifold, oxygen inlet flange (216) for providing support to the manifold, four tapered nozzles (217) directing at angle 45 ° inside the main air pipe, and supporting plate (218) for support of said manifold.
20. A mixing device as claimed in claim 19 wherein said device is provided with nozzles having circular or rectangular slots for directing the flow of oxygen inside air in the main air pipe.
21. A mixing device as claimed in claim20 wherein said device is provided with nozzles having circular slots.
22. A mixing device as claimed in claims 19-21, wherein said nozzles are oriented at an angle of 30 ° - 45° along the circumference of the combustion pipe.
23. A mixing device as claimed in claim 22, wherein said nozzles are preferably oriented at an angle of 45° along the circumference of the combustion pipe.