DESC:FIELD
The present disclosure relates to a process for production of syngas. Particularly, the present disclosure envisages a process for production of syngas in a high pressure fluidized bed gasifier.
DEFINITION
Cold gas efficiency is the ratio of the amount of chemical energy in syngas to the amount of chemical energy in the carbonaceous material, from which the syngas is produced.
BACKGROUND
The conventional processes for the gasification of biomass, fossil fuels and wastes, using gasification systems, are used to produce syngas. The syngas is further converted into liquid hydrocarbons. These liquid hydrocarbons can be utilized in internal combustion gas engines, gas turbines, dual-fuel diesel engines, fuel cells and the like. The gasification systems typically use fixed bed, fluidized bed, and jet stream or entrained flow gasifiers for gasifying the solid fuel.
The conventional processes for the production of syngas comprise the following steps:
? introducing carbonaceous material into a gasifier;
? introducing a mixture steam and oxygen into the gasifier; and
? fluidize the carbonaceous material by the mixture of steam and oxygen to produce syngas.
It is observed that the conventional processes for the production of syngas have the following drawbacks, namely:
? the carbon conversion efficiency is low;
? the calorific value of the product gas is low and inconsistent; and
? the overall efficiency of the process is low.
Hence, in order to overcome the drawbacks associated with the conventional processes, there is a need for a process for the production of syngas (product gas) that obviates one or more drawbacks of the conventional process.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to provide a process for producing syngas by gasification of solid carbonaceous material.
Another object of the present disclosure is to provide a process for producing syngas with better control of the circulation rate of the solid particles.
Yet another object of the present disclosure is to provide a process for producing syngas that has better carbon conversion efficiency.
Still another object of the present disclosure is to provide a process for producing syngas that has better calorific value.
Yet another object of the present disclosure is to provide a process for producing syngas that has a better overall efficiency.
Still another object of the present disclosure is to provide a process for producing syngas with better control of the bed height/depth of the carbonaceous material.
Yet another object of the present disclosure is to provide a process for producing syngas with better control of the oxygen-to-fuel ratio and the steam-to-fuel ratio and better control over the carbon monoxide-to-hydrogen ratio in the syngas thereby reducing the methane content in the syngas, so as to provide syngas amenable for liquid fuel generation.
Still another object of the present disclosure is to ameliorate one or more drawbacks associated with the conventional process of syngas production.
These and other objects of the present disclosure will be more apparent from the following description.
SUMMARY
The present disclosure provides a process for the production of syngas. During the process, carbonaceous material is pressurized above the atmospheric pressure. The pressurized carbonaceous material is then introduced into a gasifier in a region having low oxygen content. The carbonaceous material is further fluidized by a mixture of gases to produce syngas comprising un-reacted carbonaceous material particulates. These un-reacted carbonaceous material particulates are then separated and recycled into the gasifier in a region that has excess oxygen content thereby increasing the overall gasification efficiency.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The disclosure will now be described with reference to the accompanying non-limiting drawings:
Figure 1 illustrates a gasifier for the production of syngas in accordance with the present disclosure.
DETAILED DESCRIPTION
The disclosure will now be described with reference to the accompanying embodiments, which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
The embodiments herein, the various features, and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
The conventional processes for the production of syngas have several drawbacks, such as
? low carbon conversion efficiency;
? low and inconsistent calorific value of the product gas; and
? low efficiency of the conventional process.
The present disclosure therefore envisages a process for the production of syngas that obviates at least one drawback associated with the conventional processes.
Figure 1 illustrates a gasifier 100 for the production of syngas in accordance with the present disclosure. The gasifier 100 includes a feeding arrangement 104, 106 and 108, a screw conveyor 110, a gasification unit 118 that comprises a pair of side walls S1 and S2, a distributor plate 120, a distributor plenum 122, a first discharge conduit 129, a cooling cum conveying device 131, a first cyclone separator 136, a first standpipe 140, a loop seal 142, a recycle conduit 143, a second cyclone separator 138, a second discharge conduit 139, a collector 144, a plurality of coolers 146 and 148, and a purifier 150.
In accordance with the present disclosure, the carbonaceous material 102 is introduced to the gasifier 100 via a feeding arrangement 104, 106 and 108. In accordance with one embodiment, a mixture of coal and pet coke can be introduced to the gasifier 100. The feeding arrangement 104, 106 and 108 comprises a first hopper 104, a second hopper 106 and a third hopper 108. The carbonaceous material 102 is introduced in the first hopper 104 at atmospheric pressure. In accordance with one embodiment, the carbonaceous material 102 is high ash content coal. In accordance with one embodiment, the amount of ash in the carbonaceous material ranges from 35% to 42%. The carbonaceous material from the first hopper 104 is then fed into the second hopper 106 and pressurized above atmospheric pressure. A valve v1 between the first hopper 104 and the second hopper 106 is configured to selectively allow the flow of the carbonaceous material from the first hopper 104 to the second hopper 106. The valve v1 also seals the second hopper 106 so that it can be pressurized. The pressurized carbonaceous material from the second hopper 106 is further introduced into the third hopper 108 via a valve v2 where the carbonaceous material is maintained at high pressure. The pressurized carbonaceous material from the third hopper 108 is introduced into the screw conveyor 110 via a third valve v3. In accordance with the present disclosure, the screw conveyor 110 is adapted to convey the pressurized carbonaceous material from the third hopper 108 to the gasification unit 118 along with a first portion of steam 114 via a first inlet port a1 configured
? near an operative lower end; and
? on the side wall S1;
of the gasification unit 118.
In accordance with the present disclosure, the carbonaceous material is introduced into the gasification unit 118 in a region of the gasification unit 118 having low oxygen content.
The distributor plenum 122 is attached to the operative lower end of the gasification unit 118. A second inlet port a2 is configured on the distributor plenum 122. The distributor plate 120 is disposed in the distributor plenum 122 and is attached to the operative lower end of the gasification unit 118. A mixture of gases comprising oxygen and steam (in a predetermined ratio) is introduced into the distributor plenum 122 via the second inlet port a2.
In accordance with one embodiment of the present disclosure, oxygen and steam are pre-mixed in a pre-determined ratio.
In accordance with the present disclosure, air is not introduced into the distributor plenum 122, instead, the mixture of oxygen and steam is introduced into the distributor plenum 122.
In accordance with another embodiment of the present disclosure, the ratio of oxygen and steam is in the range of 0.6 to 0.9.
In accordance with the present disclosure, the mixture of gases is introduced into the distributor plenum 122 proximal to the distributor plate 120.
In accordance with one embodiment of the present disclosure, the distributor plate 120 is conical with a plurality of tangential apertures (not shown in figure 1) configured thereon.
The distributor plate 120 is adapted to facilitate the passage of the mixture of gases into the gasification unit 118. The mixture of gases fluidizes the carbonaceous material and temperature is maintained between 800 and 1050 ºC and at a pressure up to 30 bars.
In accordance with one embodiment of the present disclosure, fluidization of the carbonaceous material by the mixture of gases is typically in a bubbling bed fluidization.
In accordance with the present disclosure, introduction of the carbonaceous material in a region having relatively less oxygen and fluidization of the carbonaceous material facilitates instantaneous volatilization and thermal cracking of the carbonaceous material to produce syngas. The reaction of the carbonaceous material with the oxygen and steam while being subjected to fluidization produces fluidized reaction products comprising syngas, un-reacted carbonaceous material particulates, methane, carbon-monoxide, hydrogen, and ash (fines).
It is necessary to reduce the production of methane along with the syngas so that the syngas can be used for the generation of liquid hydrocarbons. In accordance with the present disclosure, the ratio of oxygen to carbonaceous material and the ratio of steam to carbonaceous material are varied to maintain the temperature between 800 and 1050 ºC, thereby suppressing the generation of methane to less than 2 to 3 %.
In accordance with the present disclosure, the ratio of oxygen to carbonaceous material is in the range of 0.4 to 0.6.
In accordance with the present disclosure, the ratio of steam to carbonaceous material is in the range of 0.5 to 0.9.
In accordance wvth one embodiment, optimizing the ratio of oxygen to carbonaceous material and the ratio of steam to carbonaceous material provides better control over the ratio of carbon monoxide to hydrogen ratio in the syngas.
In accordance with the present disclosure, a deep bed height of the carbonaceous material inside the gasification unit 118 is preferred. The deep bed height of the carbonaceous material inside the gasification unit 118 provides higher residence time of the carbonaceous material inside the gasification unit 118. Due to the higher residence time of the carbonaceous material in the gasification unit 118, the conversion efficiency of the carbonaceous material is improved, thereby resulting in an increased yield of the syngas. Typically, the residence time of the carbonaceous material in the gasification unit 118 ranges from 30 minutes to 60 minutes.
In accordance with the present disclosure, depending upon the characteristics of the carbonaceous material (particle size) and the reactivity of the carbonaceous material with the mixture of steam and oxygen, the residence time of the carbonaceous material in the gasification unit 118 ranges from 30 minutes to 60 minutes. Due to this, the conversion efficiency of the carbonaceous material ranges from 85 to 95%.
Further, in accordance with the present disclosure, the sidewalls S1 and S2 of the gasification unit 118 have varying cross-section from the operative lower end to the operative upper end of the gasification unit 118. The varying cross-section of the side walls S1 and S2 increases the residence time of the carbonaceous material in the gasification unit 118, thereby resulting in increased conversion efficiency of the carbonaceous material.
In accordance with the present disclosure, fluidization of the carbonaceous material at the high pressure (up to 30 bars) leads to entrainment of the un-reacted carbonaceous material particulates in the syngas. In order to use the syngas for further applications, it is imperative to remove the entrained particulates. In accordance with the present disclosure, the syngas entrained with particulates is introduced into the first cyclone separator 136, wherein at least a part of the carbonaceous particulates entrained in the syngas is separated. The separated carbonaceous particulates are captured and are recycled to the gasification unit 118. This increases the conversion efficiency of the processes, wherein comparatively high amount of the carbonaceous material is converted into syngas. This in turn leads to increase in the yield of the syngas.
More specifically, the syngas comprising un-reacted carbonaceous material particulates is discharged from the gasification unit 118 via a first outlet port o1 that is configured at an operative upper end and side wall S2 of the gasification unit 118. After the discharge of the syngas comprising the un-reacted carbonaceous material particulates from the gasification unit 118, it is then introduced into the first cyclone separator 136 via a first opening f1. A portion of the un-reacted carbonaceous material particulates is separated in the first cyclone separator 136. The portion of the separated un-reacted carbonaceous material particulates is introduced into the gasification unit 118 via a circulation loop along with a second portion of steam 115.
In accordance with the present disclosure, the circulation loop comprises the first standpipe 140 that extends from an operative bottom surface of the first cyclone separator 136, a loop seal 142 and a recycle conduit 143. The loop seal 142 is provided to avoid leakage of oxygen directly into the first cyclone separator 136. The portion of the separated un-reacted carbonaceous material particulates passing through the circulation loop is cooled due to heat loss and endothermic reactions. The separated un-reacted carbonaceous material particulates are recycled into the gasification unit 118 in a region close to the distributor plate 120 having excess oxygen content. This facilitates in the oxidation of the recycled un-reacted carbonaceous material particulates, which results in increasing the temperature of the recycled carbonaceous material and providing temperature modulation in the region having excess oxygen content through exothermic reactions. Thus, recycling of the un-reacted carbonaceous material particulates into the gasification unit 118 increases the overall efficiency of the gasification process.
In accordance with one embodiment of the present disclosure, the rate at which the un-reacted carbonaceous material particulates are recycled into the gasification unit 118 can be controlled.
The syngas that is discharged out from the first cyclone separator 136 is introduced into the second cyclone separator 138 via a second opening f2. This can be an optional step. The second cyclone separator further removes/purifies the syngas by removal of the carbonaceous material entrained therein.
More specifically, the second cyclone separator 138 is adapted to receive the syngas discharged from the first cyclone separator 136 via a first opening d1. The second cyclone separator 138 is adapted to separate the portion of the un-reacted carbonaceous material particulates entrained in the syngas. The portion of the un-reacted carbonaceous material particulates is separated and collected in the collector 144 via the second discharge conduit 139 that extends from an operative bottom surface of the second cyclone separator 138. The un-reacted carbonaceous material particulates from the collector 144 are discharged at 135.
In accordance with one embodiment of the present disclosure, the collector 144 is a hopper.
In accordance with the present disclosure, the syngas is discharged from a second opening d2 of the second cyclone separator 138.
The syngas from the second cyclone separator 138 is then cooled in the plurality of coolers 146 and 148. The cooled syngas is further purified in the purifier 150 to obtain a purified syngas 152.
In accordance with one embodiment of the present disclosure, the purified syngas is introduced into a Fischer-Tropsch reactor (not shown in figure 1) to convert the purified syngas into liquid hydrocarbons.
In accordance with the present disclosure, a portion of the purified syngas is re-circulated into the gasification unit 118 by a re-circulation pump 154.
In accordance with one embodiment of the present disclosure, the carbonaceous material from the screw conveyor 110 is introduced into the gasification unit 118 along with the first portion of steam 114 and a first portion of the purified syngas 116.
In accordance with another embodiment of the present disclosure, the portion of the un-reacted carbonaceous material particulates separated in the first cyclone separator 136 is introduced into the gasification unit 118 along with the second portion of the steam 115 and a second portion of the purified syngas 117.
The ash produced during the process of converting the carbonaceous material to syngas, is discharged through the first discharge conduit 129 that extends outwards from an operative bottom end of the distributor plenum 122.
In accordance with one embodiment of the present disclosure, the distributor plate 120 is conical to provide easy discharge of ash that becomes heavy due to agglomeration through the first discharge conduit 129.
In accordance with the present disclosure, the first discharge conduit 129 comprises means for cooling the ash using cooling water. An inlet 126 and an outlet 128 are configured on the first discharge conduit 129 to facilitate the inlet and the outlet of the cooling water from the first discharge conduit 129. The ash produced in the gasification unit 118 is further cooled in the cooling cum conveying device 131 via a second outlet port o2 by means of cooling water. An inlet 130 and an outlet 132 are configured on the cooling cum conveying device 131 to facilitate the inlet and the outlet of the cooling water from the cooling cum conveying device 131. The cooled ash from the cooling cum conveying device 131 is discharged at an ash discharge outlet 134 to a lock hopper system for depressurization and disposal.
The process that is carried out in the gasifier 100 of the present disclosure provides,
• the conversion efficiency of the carbonaceous material in the range of 85-95%;
• the syngas of consistent calorific value and composition;
• the syngas having a calorific value in the range of 900-1500 kcal/Nm3; and
• a cold gas efficiency in the range of 60-70% (which is dependent upon the ash content in the carbonaceous material).
TECHNICAL ADVANCEMENT
The process for the production of syngas in the gasifier of the present disclosure has several technical advantages including, but not limited to, the realization of:
• increased conversion efficiency of the carbonaceous material into syngas;
• improved overall gasification efficiency;
• the carbon conversion efficiency is 85-95%, which is obtained in approximately 30 to 60 minutes;
• the syngas produced has a calorific value in the range of 900-1500 kcal/Nm3;
• a cold gas efficiency is in the range of 60-70 %;
• provides control of the oxygen-to-fuel ratio and the steam-to-fuel ratio for obtaining better control over the carbon monoxide-to-hydrogen ratio in the syngas;
• reduced formation of methane along with the syngas; and
• the process produces syngas having a required ratio of hydrogen and carbon monoxide for conversion into liquid fuels.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the invention as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the invention, unless there is a statement in the specification specific to the contrary.
In view of the wide variety of embodiments to which the principles of the present invention can be applied, it should be understood that the illustrated embodiments are exemplary only. While considerable emphasis has been placed herein on the particular features of this invention, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principle of the invention. These and other modifications in the nature of the invention or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation. ,CLAIMS:1. A process for the production of syngas, said process comprising the following steps:
? pressurizing a carbonaceous material in a feeding arrangement at a first pre-determined pressure;
? introducing the carbonaceous material at said first pre-determined pressure from said feeding arrangement into a gasifier in a region having low oxygen content;
? introducing a mixture of gases comprising oxygen and steam into said gasifier from a gas source via a distributor plenum;
? fluidizing said carbonaceous material at a pre-determined temperature and at a second pre-determined pressure by said mixture of gases to produce syngas comprising un-reacted carbonaceous material particulates; and
? separating said un-reacted carbonaceous material particulates and recycling said un-reacted carbonaceous material particulates into said gasifier in a region having excess oxygen content.
2. The process as claimed in claim 1, wherein the carbonaceous material is high ash content coal.
3. The process as claimed in claim 2, wherein the amount of ash in the carbonaceous material ranges from 35 % to 42 %.
4. The process as claimed in claim 1, wherein said first pre-determined pressure is above atmospheric pressure.
5. The process as claimed in claim 1, wherein the ratio of oxygen to steam is in the range of 0.6 to 0.9.
6. The process as claimed in claim 1, wherein the ratio of oxygen to carbonaceous material is in the range of 0.4 to 0.6.
7. The process as claimed in claim 1, wherein the ratio of steam to carbonaceous material is in the range of 0.5 to 0.9.

8. The process as claimed in claim 1, wherein said mixture of gases is introduced into said gasifier in proximity to a distributor plate disposed in said distributor plenum.
9. The process as claimed in claim 4, wherein said un-reacted carbonaceous material particulates are recycled into said gasifier in proximity to said distributor plate.
10. The process as claimed in claim 1, wherein the pre-determined temperature ranges from 800 to 1050 ºC.
11. The process as claimed in claim 1, wherein the second pre-determined pressure is up to 30 bars.
12. The process as claimed in claim 1 has conversion efficiency, of converting said carbonaceous material to said syngas, in the range of 85 to 95%.
13. The process as claimed in claim 1, wherein the calorific value of said syngas produced in said gasifier ranges from 900 to 1500 kcal/Nm3.