DESC:FIELD
The present disclosure relates to the field of chemical engineering. Particularly, the present disclosure relates to a method for producing syngas.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
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.
Sensible heat is heat exchanged by a system that changes the temperature of the system.
BACKGROUND
Today, in India, gasification is being considered as an effective option for addressing the increasing energy demands. Syngas produced by gasification of raw materials, particularly carbonaceous materials, can be used in multifarious applications, such as generating electricity using gas engines and gas turbines; producing synthetic petroleum, chemicals, etc., and the like.
Typically, syngas is generated by converting carbonaceous materials such as coal, biomass, municipal solid wastes (MSW) in various reactors like moving bed gasifiers, entrained flow gasifiers and fluidized bed gasifiers. Entrained flow gasifiers are commonly used for high rank coals, such as Anthracite and pet coke, having less reactivity and requiring a higher operating temperature for the gasification. Such reactors are quite complex as they need to be supported by pure oxygen as a reactant. Hence, entrained flow gasifiers are economically feasible only beyond hundreds of mega Watt of thermal capacities.
Moving bed or fixed bed gasifiers, typically, need raw materials (carbonaceous materials) of size 50 mm to 75 mm, so that they don’t choke the flow inside the gasifiers. The ash content in the raw materials also affects the performance and operation of the gasifiers. Hence, Indian ‘B’ grade type or equivalent coal, which is quite expensive, is used as a raw material for such gasifiers. Moreover, using the moving bed gasifiers, large quantity of tar is generated in the syngas, which needs to be separated in post processing of the syngas.
Among the above mentioned gasifiers, fluidized bed gasifiers are beneficial; this is because, in the fluidized bed gasifiers:
• the method is carried out at isothermal conditions;
• low grade fuels can be used;
• multiple fuels can be used;
• the consumption of oxygen is moderate;
• thermal output per unit area is higher than moving bed gasifiers;
• tar yields can be controlled through operating conditions and catalytic activity of bed materials;
• scale-ups are more reliable and proven; and
• the cost for operating the fluidized bed gasifiers, as compared to the entrained bed gasifiers, is less.
There are different types of carbonaceous materials like coal, biomass, peat and pet coke that can be used as fuels in gasifiers for producing syngas. Various types of coals, such as Indonesian coals and Indian coals, are abundantly available in India that can be used as a feedstock in gasifiers. Compared to Indian coals, Indonesian coals are economical to be used as a feedstock in gasifiers. Various grades of Indian coals are also feasible for gasification. Indian coals are generally classified into different grades, viz., A, B, C, D, E, F, and G, depending upon the calorific value, ash content and moisture content of the carbonaceous material.
In a conventional fluidized bed gasifier, gasification of the above mentioned coals is carried out at a temperature in the range of 800ºC to 1000ºC. It has been found that operating the gasifier over the mentioned temperature range leads to the generation of tar, fly-ash, and low calorific of the syngas. This is because; the mentioned temperature range does not take into consideration the following factors that affect the performance of the fluidized bed gasifiers:
• clinker formation;
• fly-ash generation;
• generation of a large amount of un-burnt carbon in ash;
• tar generation; and
• syngas generation of low calorific value.
Further, an issue with the conventional gasification is that the syngas produced is cooled using water, thereby resulting in the generation of a large quantity of phenolic water that cannot be directly released into the environment due to the industrial norms and environment protection laws. Alternative means, such as radiant syngas cooler (RSC), convective syngas cooler (CSC), and the like for cooling the syngas or recovering heat from the syngas are available; however such means are expensive to implement; prone to fouling; and difficult to clean.
There is, therefore, felt a need for an alternative method to produce syngas that obviates the above mentioned drawbacks.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide an alternative method for producing syngas.
Another object of the present disclosure is to provide an alternative method for producing syngas by gasification of different grades of a carbonaceous material.
Still another object of the present disclosure is to provide an alternative method for producing syngas by gasification of different particle size of a carbonaceous material.
Yet another object of the present disclosure is to provide an alternative method for producing syngas that obviates reduction in the carbon conversion efficiency of a carbonaceous material.
Still another object of the present disclosure is to provide an alternative method for producing syngas that obviates clinker formation.
Yet another object of the present disclosure is to provide an alternative method for producing syngas that obviates generation of fly-ash and tar.
Still another object of the present disclosure is to provide an alternative method for producing syngas that obviates generation of a large amount of un-burnt carbon in ash.
Yet another object of the present disclosure is to provide an alternative method for producing syngas that attenuates reduction in the calorific value of syngas.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure provides a method for producing syngas. The method is carried out in the steps described herein below.
In the first step, air can be pre-heated to form pre-heated air.
In the second step, the pre-heated air can be used to fluidize Indonesian coals at a temperature within a first range between 825ºC and 900ºC or Indian ‘B’ to ‘E’ grade coals within a second range between 900ºC and 970ºC in the presence of a bed material at a pressure in the range of 0 to 0.5 bar above atmospheric pressure or at sub-atmospheric pressure to produce a raw syngas with entrained dust particles and tar.
In the third step, the raw syngas can be cooled above the dew point of tar at a temperature in the range of 150ºC to 300ºC to obtain cooled raw syngas.
The third step of cooling can be carried out by allowing the raw syngas and a cooling fluid to pass through a shell and tube heat exchanger.
The temperature of the cooling fluid can be in the range of 25°C to 400°C.
The cooling fluid can be air.
In the fourth step, the entrained dust particles can be separated from the cooled raw syngas.
In the fifth step, the entrained tar can be separated from the cooled raw syngas from which the entrained dust particles have been removed to obtain syngas.
The second step of fluidization can be carried out in the presence of a bed material selected from the group consisting of magnesium iron silicate, dolomite, and silica sand.
An additive can be introduced into the bed material.
The additive can be at least one selected from the group consisting of calcined dolomite (OCa•OMg), natural and sintered olivines ((Mg, Fe)2 SiO4), a nickel (Ni)-olivine catalyst pretreated with magnesium oxide, dicyclopentadienyl iron, and nickel sulfamate.
The particle size of the Indonesian or Indian coals can be in the range 0.5 mm to 8 mm.
The syngas can be used in at least one application selected from the group consisting of electricity generation, an intermediate for producing synthetic petroleum, a fuel for internal combustion engines.
The calorific value of the syngas can be greater than 1100 kcal/ Nm3.
The cold gas efficiency of the method can be greater than 70 percent.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
A method for producing syngas will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates a flow diagram depicting a method for producing syngas in accordance with the present disclosure.
Table illustrates a list of the following reference numerals:
Components Reference numeral
Feeder 2
Gasifier 4
Pre-heater 6
Re-circulated 7
Cooler 8
Dust collection unit 10
Tar removal unit 12
Application 14

DETAILED DESCRIPTION
As described herein above, there are certain limitations associated with a conventional gasification carried out in fluidized bed gasifiers, for instance:
• clinker formation;
• fly-ash generation;
• generation of a large amount of un-burnt carbon in ash;
• tar generation; and
• syngas generation of low calorific value.
Moreover, a large quantity of phenolic water is generated during the cooling of the syngas leaving the fluidized bed gasifiers. The phenolic water cannot be directly released into the environment due to the industrial norms and environment protection laws.
The present disclosure, therefore, envisages a method, particularly an integrated method, for producing syngas that obviates one or more of the above mentioned drawbacks. The method is implemented on medium scale gasifiers; this is because, the amount of energy consumed or required for gasifying the carbonaceous material therein is significantly less as compared to that required in high scale gasifiers.
The method for producing syngas is described with reference to Figure 1.
Coal containing raw materials, i.e., carbonaceous materials, are introduced into a feeder (2). From the feeder (2), the carbonaceous materials are fed into a gasifier (4), more particularly a fluidized bed gasifier. The carbonaceous materials are fluidized or treated in the gasifier (4) by a fluidizing medium, preferably air. In accordance with one embodiment of the present disclosure, steam along with air can be used the fluidizing medium.
The air is pre-heated in a pre-heater (6) to form pre-heated air before introducing into the gasifier (4). The pre-heated air is introduced into the gasifier (4) for fluidizing Indonesian coals at a temperature within a first range between 825ºC and 900ºC or Indian ‘B’ to ‘E’ grade coals within a second range between 900ºC and 970ºC, in the presence of a bed material, at a pressure in the range of 0 to 0.5 bar above atmospheric pressure or at sub-atmospheric pressure, to produce a raw syngas with entrained dust particles and tar.
The raw syngas is then cooled above the dew point of tar at a temperature in the range 150ºC to 300ºC to obtain cooled raw syngas. From the cooled raw syngas, the entrained dust particles in the cooled raw syngas are separated using a dust collection unit (10). Downstream of the dust collection unit (10), tar is removed from the cooled raw syngas using a tar removal unit (12).
The pressure inside the gasifier (4) is maintained in the range of 0 to 0.5 bar above the atmospheric pressure to avoid use of moving parts such as an induced draft fan, and the like in the downstream, thereby attenuating high temperature and corrosion issues of the moving parts. The overall size of the gasifier (4) can be reduced by maintaining the aforementioned pressure range in the gasifier (4).
The gasification of the carbonaceous material can also be carried out under sub-atmospheric pressure conditions by using at least one of a forced draft system and an induced draft system.
The particle size of the Indonesian coals or Indian ‘B’ to ‘E’ grade coals can be in the range of 0.5 mm to 8 mm.
The above mentioned temperature range, i.e., between 825ºC and 900 ºC for Indonesian coals and between 900ºC and 970ºC for Indian coals, is a critical parameter in the present method for gasifying the carbonaceous materials. This is because; as mentioned herein above, the temperature range at which the carbonaceous materials are fluidized is responsible for controlling the factors such as clinker formation, generation of low calorific value of syngas, decrease in the carbon conversion efficiency of the carbonaceous materials, generation of tar and fly-ash and the like.
Indonesian coals include a moisture content of greater than 20 % and an ash content of less than 15%.
In accordance with the present disclosure, it is necessary to treat or fluidize the Indonesian coals at a temperature between 825ºC and 900ºC, so as to obviate the following drawbacks during the method carried out in the gasifier (4):
• generation of low calorific value of the syngas;
• clinker formation; and
• generation of tar along with the syngas.
Typically, the Indian coals are treated or fluidized at a temperature range higher than the Indonesian coals, i.e., at a temperature between 900ºC and 970ºC. This is because; the Indian coals are less reactive as compared to the Indonesian coals. Further, typically, the initial deformation temperatures of the Indian coals are above 1100ºC, thereby obviating the clinker formation up to 970ºC. Therefore, it is necessary to treat or fluidize the Indian coals at a temperature between 900ºC and 970ºC.
The continuous circulation of the pre-heated air in the gasifier (4), for maintaining the above mentioned temperature ranges, i.e., between 825ºC and 900ºC for the Indonesian coals and between 900ºC and 970ºC for the Indian coals, is necessary. If the temperature for the Indian coals and Indonesian coals exceeds their respective temperature range, then the clinker are formed along with the production of the syngas, thereby affecting the efficiency of the method or the performance of the gasifier (4).
Further, if the temperature for treating the Indian coals and Indonesian coals falls below their respective temperature range, then the method will facilitate the generation of tar along with the production of the syngas. Also, the carbon conversion efficiency, i.e., the conversion of the carbonaceous materials, to produce the syngas will be reduced. This results in reducing the efficiency of the method or the performance of the gasifier (4).
The step of treating or fluidizing the carbonaceous materials can be carried out in the presence of a bed material. The bed material can be at least one selected from the group consisting of magnesium iron silicate, dolomite, and silica sand.
The bed material facilitates cracking of tar, absorption or capture of sulfur components, for example oxides of sulfur, and reducing fouling problems associated with certain ash minerals such as iron, sodium, and potassium.
An additive can also be introduced into the bed material. The additive can be at least one selected from the group consisting of calcined dolomite (OCa•OMg), natural and sintered olivines ((Mg, Fe)2 SiO4), a nickel (Ni) - olivine catalyst pretreated with magnesium oxide, dicyclopentadienyl iron, and nickel sulfamate.
The additive facilitates enhancing cracking of tar, absorption or capture of sulfur components, for example oxides of sulfur.
The average particle size of the bed material is also a crucial parameter in the fluidization. This is because; the average particle size changes after the method is repetitively carried out, thereby affecting the performance thereof. Hence, it is necessary to control the particle size distribution of the bed material, which is achieved by periodically withdrawing the bed material from the gasifier (4) and replacing it with a fresh bed material for smooth operation of the gasifier (4). The optimal frequency of the withdrawal is dependent on the type or grades of carbonaceous materials, thereby obviating clinker formation in the gasifier (4).
In order to use syngas in various applications, it is necessary to reduce the temperature or cool the raw syngas leaving the gasifier (4) and separate the entrained dust particles and tar from the raw syngas to obtain the syngas.
Typically, the particle size of the entrained dust particles is below 500 microns.
After leaving the gasifier (4), the raw syngas is cooled in a cooler (8) by contacting the raw syngas with a cooling fluid to cool the raw syngas to obtain the cooled raw syngas.
The temperature of the raw syngas leaving the gasifier (4) can be in the range of 825°C to 970°C.
In accordance with one embodiment of the present disclosure, the cooling fluid can be a thermic or non-thermic fluid.
In accordance with a preferred embodiment of the present disclosure, the cooling fluid can be air.
The cooler (8) can be at least one heat exchanger.
In a preferred embodiment of the present disclosure, the heat exchanger is a shell and tube heat exchanger.
The temperature of the cooling fluid can be in the range of 25ºC to 400ºC.
The raw syngas can be cooled to a temperature in the range of 150ºC to 300ºC.
The shell and tube heat exchanger can be used for cooling the raw syngas leaving the gasifier (4). Preferably, the raw syngas to be cooled is allowed to pass through a plurality of tubes of the shell and tube heat exchanger and the cooling fluid is allowed to pass through a shell of the shell and tube heat exchanger, thereby facilitating extraction of the sensible heat of the raw syngas (heat recovery from the raw syngas) by heat transfer between the raw syngas and the cooling fluid, to obtain the cooled raw syngas.
The heated air leaving the shell and tube heat exchanger can be re-circulated (7) into the gasifier (4) for maintaining a desired temperature range, thereby making the method energy efficient.
The heated air can also be utilized or returned to the step of pre-heating, for pre-heating the air, thereby making the method energy efficient (not shown in Figure 1).
Moreover, the heat recovery from the raw syngas is necessarily performed above the dew point of tar entrained in the raw syngas, thereby avoiding the condensation of tar within the tubes of the shell and tube heat exchanger. The heat recovered below the dew point results in the condensation of tar within the tubes, thereby affecting the performance of the shell and tube heat exchanger.
Further, the raw syngas leaving the gasifier (4) facilitates in the cleaning of the inner surfaces of the tubes. As mentioned hereinbefore, the particle size of the entrained dust particles can be below 500 microns, and while the raw syngas flows through the tubes, the entrained dust particles cause scavenging action, thereby cleaning the inner surfaces of the tubes. The scavenging action can be enhanced by increasing the turbulence or controlling the flow of the raw syngas through the tubes.
The cooled raw syngas leaving the cooler (8) is allowed to pass through the dust collection unit (10) for separating the entrained dust particles from the cooled raw syngas.
The dust collection unit (10) can be at least one selected from the group consisting of a cyclone separator, a bag filter, and an electrostatic precipitator.
Further, depending upon the requirement, the cooled raw syngas from which the entrained dust particles have been removed is allowed to pass through the tar removal unit (12) to obtain the syngas, more particularly clean syngas.
The tar removal unit (12) can be a scrubber.
The syngas or cleaned syngas leaving the tar removal unit (12) can be used in at least one application (14) selected from the group consisting of electricity generation, an intermediate for producing synthetic petroleum, a fuel for internal combustion engines.
The method of the present disclosure is capable of providing a cold gas efficiency of greater than 70 percent; and producing the syngas having a calorific value of greater than 1100 kcal/ Nm3.
TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a method that:
• produces syngas using different grades of a carbonaceous material;
• produces syngas using different particle size of a carbonaceous material;
• produces syngas having a calorific value of greater than 1100 kcal/Nm3;
• increases the carbon conversion efficiency; and
• provides a cold gas efficiency of greater than 70%.
The disclosure has been 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 and 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 foregoing description of the specific embodiments so fully revealed 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.
,CLAIMS:1. A method of producing syngas, said method comprising the following steps:
(a) pre-heating air to form preheated air;
(b) fluidizing with said preheated air in the presence of a bed material Indonesian coals at a temperature within a first range between 825°C and 900°C or Indian ‘B’ to ‘E’ grade coals within a second range between 900°C and 970°C, at a pressure in the range 0 to 0.5 bar above atmospheric pressure or at sub-atmospheric pressure, to produce a raw syngas with entrained dust particles and tar;
(c) cooling said raw syngas above the dew point of tar at a temperature in the range 150°C to 300°C to obtain cooled raw syngas;
(d) separating said dust particles entrained in said cooled raw syngas; and
(e) separating tar from said cooled raw syngas, from which dust particles have been removed, to obtain syngas.
2. The method as claimed in claim 1, wherein said bed material is selected from the group consisting of magnesium iron silicate, dolomite, and silica sand.
3. The method as claimed in claim 1, wherein an additive is introduced into said bed material, wherein said additive is at least one selected from the group consisting of calcined dolomite (OCa•OMg), natural and sintered olivines ((Mg, Fe)2 SiO4), a nickel (Ni) - olivine catalyst pretreated with magnesium oxide, dicyclopentadienyl iron, and nickel sulfamate.
4. The method as claimed in claim 1, wherein the particle size of said Indonesian or Indian coals is in the range of 0.5 mm to 8 mm.
5. The method as claimed in claim 1, wherein said syngas is used in at least one application selected from the group consisting of electricity generation, an intermediate for producing synthetic petroleum, a fuel for internal combustion engines.
6. The method as claimed in claim 1, wherein said syngas is has a calorific value greater than 1100 kcal/ Nm3.
7. The method as claimed in claim 1, wherein the cold gas efficiency of said method is greater than 70 percent.
8. The method as claimed in claim 1, wherein said step c) of cooling is carried out by allowing said raw syngas and a cooling fluid to pass through a shell and tube heat exchanger, wherein said cooling fluid is air.
9. The method as claimed in claim 8, wherein the temperature of said raw syngas is in the range of 825°C to 970°C and the temperature of said cooling fluid is in the range of 25°C to 400°C.
10. The method as claimed in claim 8, wherein said cooling fluid is allowed to pass through the shell side of said heat exchanger and said raw syngas is allowed to pass through the tube side of said shell and tube heat exchanger.