JP2000038589A - Cleaning of product gas from hydrocarbon fuel and cleaning system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cleaning system including a process for removing volatile trace elements in a coal gasification gas. SOLUTION: This system comprises a separation and recovery process of dust 22 contg. unreacted carbon from the product gas (crude gas) 11 after a gasification process of hydrocarbon fuel such as coal 1, heavy oil, etc., then, a process adding coal ash ejected from the gasification furnace 10 as a collecting agent for removal of volatile trace gases contained in the crude gas, then, an coagulation process of minute particles, and then, a recovery process for dust such as collecting agent, etc., in the product gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system and a method for purifying gasified gas of hydrocarbon fuels such as coal and heavy oil, and more particularly to a system for removing volatile trace elements in gas. According to.

[0002]

2. Description of the Related Art In addition to raw materials for chemical synthesis, coal gas is used as fuel for fuel cells, fuel for combined power generation systems incorporating gas turbines and steam turbines, and the like. In coal gasification, coal and oxygen or air as an oxidant are supplied to a gasification furnace to mainly generate hydrogen, carbon monoxide, methane gas, and carbon dioxide. However, H ₂ S, C
It contains environmental polluting gases such as OS, NH ₃ , HCN, etc., and As, B, Be, Cd, Cl, Co, Cr, F, Hg,
Harmful elements such as Mn, Ni, Pb and Se are included. A
The content of elements such as s, B and Be is very small, and some of them remain in coal ash even after gasification, but most of them are volatilized in product gas because their compounds are volatile. ,
Need to be removed. For the removal of environmental polluting gases, wet and dry gas purification methods (referred to as low-temperature or high-temperature gas purification methods) have been developed, but effective methods for removing volatile trace elements have not yet been established.

[0003] As a method for removing volatile trace elements, a cleaning method of a generated gas is known. However, it is reported that some elements are not completely removed even by washing with water, Fuel, Vol.
(1994) and Kagaku Kougaku Ronbunsyu, Vol.23, N
o.1 (1997). For this reason, a method of removing a volatile trace element by adding a collecting agent has been studied. For example, JP-A-60-115688 discloses Hg, Cl,
Adsorbing F with limestone, Proceedings of 12th Pi
ttsburg Internatinal Coal Conference, Pittsburg (1
995), Hg with activated carbon and Cl with sodium carbonate
Is described. IEA Coal
Research Report, No. 49 (1992) states that Hg, Cd,
Zeolite as a collector for Pb, Ni, V, Z, As,
Activated carbon, silicate, alumina, silicon-based compounds, Ni-based compounds, Fe-based compounds, MgO and the like are described according to the elements. However, it does not disclose the timing of adding the trapping agent or a specific application method to a gasification plant. Japanese Patent Application Laid-Open No. 4-180817 describes that fine ash is used for removing mercury in exhaust gas, although it is not a coal-producing gas.

[0004]

SUMMARY OF THE INVENTION It is not possible to sufficiently remove volatile trace elements simply by cleaning the gas. On the other hand, it is necessary to improve the performance also in the method using the trapping agent. In addition, the volatile trace elements in the coal-producing gas are of a very large number of types, and if the supply of the trapping agent is changed for each element, the system and equipment tend to be complicated. An object of the present invention is to make it possible to remove many kinds of volatile trace elements with one kind of collecting agent in a method using a collecting agent. Another object of the present invention is to provide a method suitable for removing volatile trace elements by using a collector.

[0005]

According to the present invention, there is provided a method for removing volatile elements contained in a gasified gas of a hydrocarbon fuel by introducing a collecting agent into the gas. A method for purifying generated gas of a hydrocarbon fuel, characterized by using ash.

Further, the present invention provides a method for producing a combustible gas by gasifying coal, separating and removing char contained in the gas, and then adding coal ash particles to the gas to produce a gas. A method for purifying a coal-producing gas, comprising capturing and removing volatile elements contained by the coal ash, and then separating and removing sulfur contained in the gas.
The present invention provides a gasification step of gasifying a hydrocarbon fuel to produce a combustible gas, a dust removal step of separating and removing dust containing unreacted carbon from the product gas obtained in the gasification step, And a desulfurization step of removing sulfur from the gas after the dust removal step.
A system for purifying a generated gas of hydrocarbon fuel, comprising a coal ash addition step of adding coal ash to the gas after the dust removal step and before the desulfurization step.

Further, in the purification system, after the coal ash adding step and before the desulfurizing step, a particle aggregating step for aggregating particles contained in the gas is provided. Purification system.

In the above-mentioned purification system, it is preferable that a particle removing step for separating and removing particles agglomerated in the particle aggregating step from the gas is provided after the particle aggregating step and before the desulfurizing step. A feature of the present invention is a hydrocarbon gas generated gas purification system.

[0009] The purification system of the present invention may further include a step of returning the dust containing unreacted carbon separated and removed in the dust removal step to the gasification step.

Further, the method may include a step of cooling the gas generated in the gasification step to 750 to 850 ° C. and recovering heat before the dust removal step.

The present invention can also be applied to a generated gas purification system having a step of cooling and recovering heat immediately after the coal ash adding step. In this heat recovery step, it is desirable to cool the gas so that the water vapor in the gas does not condense.

In the present invention, it is preferable to use, as the collecting agent, fine particles obtained by pulverizing coal ash discharged from a gasification furnace. When the gasification furnace is at a high temperature and the discharged ash is molten slag, the slag is atomized and used. Further, it is preferable to apply static electricity to the aggregation of the fine particles in the gas to aggregate the coal ash,
It is desirable to spray water in order to remove the powder adhering and accumulating on the dust collecting portion of the electrostatic aggregator. By providing a water washing type particle removing step after the particle aggregating step, the exfoliated material and the washing water are directly introduced into the washing step, and are treated in the wastewater treatment step together with dust and wastewater collected in the water washing step. It becomes possible.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons why volatile trace elements cannot be removed from the investigation of the generation and removal mechanism of volatile trace elements and the understanding of the behavior in actual gasification equipment are as follows.

I) While the condensation temperature of the volatile trace element is low, the element itself has not dropped to that temperature and is in a gaseous state.

Ii) Condensed matter has an extremely small particle size and cannot be sufficiently removed by a filter or simple washing.

Iii) The reaction temperature and reaction time between the volatile trace element and the collector are insufficient, or the collector is inappropriate.

Iv) When the collector is added, the volatile trace elements in the produced gas are transferred to the char and the collector.
A large amount is selectively transferred to the collecting agent and collected. However, in the case of both powders, the separation and separation from the char do not work well, and the collecting agent incorporating the volatile trace elements has a problem. Contained in the circulation and cannot be discharged outside.

In order to remove volatile trace elements, it is necessary to comprehensively satisfy these requirements, and it is not sufficient to use only one specific item.

First, in the case of i), it is necessary to cool the produced gas to as low a temperature as possible. In particular, the boiling point of the Hg compound is low. From a practical point of view, it is preferable to cool the device to at least room temperature.

Ii) is extremely important for collecting volatile trace elements. Since the elements volatilized by gasification are condensed, the condensate alone naturally becomes extremely small. According to observation with a microscope, there are those with ten to one hundred nanometers. Since they may aggregate with each other or adhere to the surface of large particles, they are trapped to some extent by ordinary water washing. However, active measures are needed to achieve sufficient collection efficiency. It is best to apply static electricity to collect particles on the order of nanomicrons. After being agglomerated by static electricity, it was determined to be collected by a washing step.

Regarding iii), the reason why slag after gasification is selected as the collector is to promptly react with volatile trace elements. As shown in the above-mentioned prior art, as a collecting agent for volatile trace elements, although individually known, the present invention includes these effective elements in slag comprehensively and at a high concentration. New knowledge that FIG. 3 shows a plant in which pulverized coal is gasified with oxygen at 1200 to 1600 ° C. and the generated gas is washed with water, and shows how elements in the coal migrate to solid emissions. The transition rate follows the formula:

[0022]

(Equation 1)

Here, the solid discharge is slag discharged from the gasification furnace and dust scattered from the gasification furnace and collected by a downstream water washing device. Transfer rate to solid emissions is 10
What is less than 0% is the so-called volatile element,
In FIG. 3, they are As, B, Cl, and Hg. on the other hand,
The Al, Si,
Ca, Fe, Ni, and Ti-based elements have migrated more in the slag. That is, slag is a good substance for simultaneously collecting various volatile trace elements. This is the reason why slag was selected as the collecting agent. Although ash is naturally present in the char scattered from the gasification furnace, most of the ash in the char is surrounded by carbonaceous material, so that the ash is not sufficiently contacted with volatile trace elements and cannot be deposited in the reaction. In addition, single ash particles also exist in the scattered matter, but their components are close to the scattered dust in FIG. 3, and as shown in the figure, the chemical composition with volatile trace elements is far greater than that of slag. Few.

Since the slag, when discharged from the gasification furnace, is at least several mm, it is pulverized for use as a collector. This is to make the reaction with the volatile trace element proceed in a short time, and is preferably at least several μm or less. With such a particle size, the reaction is completed in the order of seconds, so that the reaction can proceed while the gas passes through the piping or the container after the supply of the trapping agent. The reaction temperature will be described later.

On the other hand, regarding iv), it is important where the collecting agent is supplied in the system. The following five cases can be considered as supply points of the collecting agent.

Immediately after the gasification step In the case of the gasification step, dust removal step, and heat recovery step, after the dust removal step In the case of the gasification step, dust removal step, and the heat recovery step, and after the heat recovery step Process, heat recovery process, dust removal process, after heat recovery process Gasification process, heat recovery process, dust removal process, after dust removal process When selecting these, the important thing is gasifier There is a char that flies from. Although this is large or small, it always exists regardless of the type of gasifier. In the gasification plant, the char is collected and returned to the gasifier again to gasify,
Maintain carbon gasification rate. It is common to perform so-called char circulation. In the above case, the collector enters the dust removal step together with the char. If these are not distinguished, the trapping agent will also be supplied again to the gasifier. Since the trapping agent has absorbed volatile trace elements, the volatile elements volatilize again by gasification again,
The concentration in the gas at the gasifier outlet will increase. For example, in FIG. 3, for As and Hg whose transfer rates to slag are extremely low, the concentration in dust scattered in the gasifier indicates that the dust removal efficiency is 9%.
In a circulation system with a 9% char recovery unit, the concentration is about 13 times the concentration in coal. That is, a large amount of volatile substances is present in the char circulating system. When a failure occurs in the char circulating system or the dust removing equipment, high-concentration powder is discharged out of the char circulating system, and the treatment becomes difficult.
Separating the char and the trapping agent also requires a drastic change in the powder properties of both, which results in excess equipment. From this, the collecting agent is supplied from a process outside the char circulating system,
Select above or

When selecting or, the problem is how to set the reaction temperature between the volatile trace element and the collector. In the reaction, the volatile trace element is desirably in a gaseous state, and the temperature is preferably higher. Therefore, it is preferably added before the heat recovery step. The condensation temperature of a volatile trace element varies depending on the element or its compound.
° C, and 80 ° C or lower for Hg compounds. On the other hand, in the dust removal step, the maximum temperature is about 850 ° C. due to the restriction of the materials of the equipment usually used, but this temperature is sufficient for the reaction. In the case of the above, the temperature is 2
It will be 50-400 ° C. This temperature is in a temperature range in which volatile trace elements condense, and is more disadvantageous in terms of reaction.However, if the particle diameter of the collecting agent is small and at least several μm or less, even in the reaction between solid phases, Proceed in a relatively short time. With such a particle size, the reaction is completed in the order of seconds, so that the reaction can proceed while the gas passes through the pipe after the supply of the trapping agent.

In summary, in order to remove the volatile trace elements generated from the gasification furnace, the reaction with the collector and the cooling of the produced gas are changed from the gas phase to the solid phase, and the generated solid phase is removed. Is an ultrafine particle, so a coagulation step is required before collecting dust.

FIG. 1 shows an embodiment of the present invention. This coal gas system has a gasification step 10, a first heat recovery step 15, a first dust removal step 20, a second heat recovery step 25, a fine particle agglomeration step 30, a second dust removal step 40, a desulfurization step 50, a desulfurizing agent regeneration. Step 60, sulfur fixing step 70, gas conversion / utilization step 80,
And a slag crushing step 90.

The coal 1 and the oxidizer 2 (oxygen or air or a mixture thereof) are sent to a gasification step 10. The gasification system includes a low temperature type (fixed bed method), a medium temperature type (fluidized bed method), a high temperature type (airflow bed method), and the like. In this embodiment, a high temperature type is used. Coal is gasified at 20-30 atm, 1200-1600 ° C. As a result, most of the ash in the coal is discharged from the gasification step 10 as molten slag 12. The remaining ash scatters from the gasifier with the char. The generated gas 11 (crude gas) containing these dusts is introduced into the first heat recovery step 15, and the temperature of the gas is reduced to 750 to 850 ° C. The generated steam 17 is used in the present system or supplied to a power generation facility in a gas conversion / utilization process 80. The gas 16 is led to the first dust removal step 20 to collect dust 22 (char) scattered from the gasification furnace. Char gasification process 1 again
Return to 0. A cyclone, a ceramic filter, a moving bed dust remover, an electrostatic precipitator or a combination thereof can be used for the dust removing device, but it is desirable that the temperature be around 800 ° C. and that the system and operation are not complicated. Therefore, in this embodiment, a cyclone was used. Since the average particle diameter of the char is tens to several tens of microns, a two-stage normal cyclone can secure a dust collection rate of 90 to 95%.
On the other hand, if the char collected at such a dust collection rate is gasified again, the total carbon efficiency of the gasifier can be reliably maintained at 98% or more. Next, a trapping agent 91 for removing volatile trace elements is added to the degassed gas 21. This is a slag part of the slag discharged from the gasifier which is branched 13
It is crushed to several μm or less in the crushing step 90. The supply amount of the trapping agent is determined according to the amount of volatile trace elements generated. Usually, coal ash is mostly Si, Al, Ca, Fe,
So-called main components of K, Mg, Na, P and Ti occupy. The proportion of so-called trace elements such as As and the like is usually 0.5 to 3 wt.
%. The effect is large if the amount of slag reacted with the volatile trace element is about two to three times the volatile trace element. This corresponds to 1 to 10 wt% of the ash content. Assuming that the amount of coal supplied to the gasifier is 100, the ash content is 5-2.
5, the amount of slag as a collecting agent is 0.05 to 2.2.
5 and a small amount with respect to the amount of coal.

The product gas to which the trapping agent has been added is supplied to the second heat recovery step 25. In the second heat recovery step 25, heat recovery is performed to a minimum temperature at which water vapor in the generated gas does not condense.
The generated steam 27 is used in the present system or used for other purposes. The water vapor saturation temperature at 20-30 atm is 21
Since it is 1 to 233 ° C., it is at least about 250 ° C. While the collecting agent flows through the piping and the heat recovery device, the reaction with the volatile trace element proceeds. Also, since the gas is cooled at the same time, condensate is generated. Subsequently, the gas 26 is guided to an electrostatic particle aggregation step 30. Here, the purpose is to coagulate volatile trace elements that do not react with the trapping agent and exist as single ultrafine particles. In addition, naturally, dust in the gas containing the collecting agent is also aggregated. The electrostatic agglomerator itself is a normal one consisting of a charging unit and a dust collection unit.However, in order to separate the powder adhered and agglomerated on the dust collection unit, the washing water used in the next second dust removal step is used. use. A part of the washing water is taken out from the water washing step, which is the second dust removal step, and the washing water is sprayed to the dust collecting portion to be separated. The peeled powder and the washing water are directly introduced into the next second dust removal step 40. In the second dust removal step 40, a water washer is used to remove the fine particles with high efficiency and to reduce the temperature of the gas to remove volatile gas having as low a boiling point as possible. The water washer is composed of a shelf and a water tank. In order to increase the contact efficiency with water as much as possible, the gas is passed through the water tank while bubbling the gas, and is further brought into countercurrent contact with water on the shelf. The temperature here is lowered to room temperature. The collecting agent flowing from the fine particle aggregating step 30 and the volatile trace elements of the solid that has been electrostatically agglomerated, and the fine dust that originally existed in the generated gas and could not be completely removed in the first dust removing step, , Are efficiently separated and removed. In addition, since separated substances such as dust settle in the water tank, by extracting these substances 42,
Discharge outside the system. The discharged dust is converted into solid waste by an existing method such as a filter press.

The gas 41 from which volatile trace elements have been removed is sent to a desulfurization step 50 for further removing H2S and COS. This is an existing technology and will not be described in detail. The gas 52 after desulfurization is sent to a gas conversion / utilization step 80 and used for chemical synthesis and power generation. The desulfurizing agent used in the desulfurizing step is regenerated in the desulfurizing agent regenerating step 60. Further, the sulfur separated in the desulfurizing agent regeneration step is fixed and recovered in the sulfur fixing step 70. Reference numeral 71 indicates recovered sulfur.

FIG. 2 shows an embodiment including only one heat recovery step. In this system, the temperature of the generated gas is reduced to 250 to 400 ° C. at a time in the heat recovery step 15, and then the char is recovered in the first dust removal step 20. Subsequently, the collecting agent 91 is added, and the collecting agent 42 is collected in the second dust removal step 40. Although the temperature of the gas added to the trapping agent 91 is lower than that in FIG. 1, it is disadvantageous in terms of the trapping reaction. However, since there is only one heat recovery step, this case also holds as a gasification system. Further, since the temperature of the generated gas entering the first dust removal step 20 is lower than that in FIG.
The dust removing device may be a filter. Other methods and operations are the same as those in FIG.

[0034]

According to the present invention, a method for removing volatile trace elements in coal gas by using coal ash discharged from a coal gasifier as a collector has been established.

[Brief description of the drawings]

FIG. 1 is a flowchart of a coal production gas purification system showing one embodiment of the present invention.

FIG. 2 is a flow chart of a coal production gas purification system showing another embodiment of the present invention.

FIG. 3 is an explanatory diagram of a solid transfer rate of elements in coal.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Coal, 2 ... Oxidizing agent, 10 ... Gasification process, 11 ... Production gas, 12 ... Molten slag, 15 ... First heat recovery process, 20
... First dust removal process, 22 ... Dust, 25 ... Second heat recovery process, 30 ... Particle aggregation process, 40 ... Second dust removal process, 50
... desulfurization step, 60 ... desulfurization agent regeneration step, 70 ... sulfur fixing step, 71 ... recovered sulfur, 80 ... gas conversion / utilization step, 90
... Slag crushing process.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D002 AA03 AA04 AA28 AA29 AA31 AC10 BA02 BA04 BA14 BA20 CA06 DA35 DA66 EA01 EA02 EA05 GA01 GB03 GB12 HA08 4D020 AA04 AA10 BA23 BA30 BB01 CA07 CA08 CD02 CD03 4H060 AA01 BB04 BB04 BB24 BB04 DD12 DD24 DD28 FF03 GG01 GG02

Claims (9)

[Claims] 1. A method for removing volatile elements contained in a gasified gas of hydrocarbon fuel by introducing a trapping agent into the gas, wherein coal ash is used as the trapping agent. A method for purifying a product gas of a hydrocarbon fuel. 2. A gasification step of gasifying a hydrocarbon fuel to produce a combustible gas; a dust removal step of separating and removing dust containing unreacted carbon from a gas produced in the gasification step; And a desulfurization step of removing sulfur from the gas after the dust removal step.
A system for purifying a generated gas of hydrocarbon fuel, comprising a coal ash addition step of adding coal ash to the gas after the dust removal step and before the desulfurization step. 3. The hydrocarbon fuel production gas purification system according to claim 2, further comprising a particle aggregation step of aggregating particles contained in the gas after the coal ash addition step and before the desulfurization step. A product gas purification system for hydrocarbon fuel. 4. The hydrocarbon fuel production gas purification system according to claim 3, wherein the particles agglomerated in the particle aggregating step are separated from the gas after the particle aggregating step and before the desulfurization step. A system for purifying generated gas of hydrocarbon fuel, comprising a particle removing step for removing. 5. A process according to claim 2, wherein the dust containing unreacted carbon separated and removed in the dust removal step is returned to the gasification step. A system for purifying generated gas of hydrocarbon fuel, comprising: 6. The hydrocarbon fuel production gas purification system according to claim 2, wherein the gas produced in the gasification step before the dust removal step is 750-8.
A system for purifying generated gas of hydrocarbon fuel, comprising a step of cooling to 50 ° C. and recovering heat. 7. The hydrocarbon fuel production gas purification system according to claim 6, further comprising a step of cooling the gas and recovering heat immediately after the coal ash addition step to such an extent that water vapor in the gas is not condensed. A product gas purification system for hydrocarbon fuel. 8. The hydrocarbon fuel product gas purifying system according to claim 3, wherein said particle aggregating step comprises a step of aggregating particles using static electricity. . 9. Combustible gas is produced by gasifying coal,
After separating and removing the char contained in the gas, coal ash particles are added to the gas to capture and remove volatile elements contained in the gas by the coal ash, and then the sulfur content contained in the gas is removed. A method for purifying coal-produced gas, comprising separating and removing coal.