JPH10296037A - Method for eliminating trace substance in high temperature reducing gasified gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate trace substance by a dry system in high temperature reducing gas in good thermal efficiency by a method wherein when a sulfur compound or the like contained in gasified gas is eliminated by a dry refining, a halogen gas component and ammonia in the gas after desulfurization are reacted with each other, and ammonium halide is separated by recipitation thereafter. SOLUTION: In gasified gas 1 at an inlet of a dry gas refining apparatus, at first H2 S and COS are eliminated by absorption with a desulfurizing apparatus 3 in which a honeycomb desulfurizing agent is filled. Then, after cooling the gasified gas after desulfurization with a cooling heat exchanger 9, HCl in the gasification gas is made CaCl by adding a basic inorganic compound 13. Since new soot and dust are generated in this case, in addition to char as a main component, a calcium compound, the other alkali metal, heavy metal, etc., are exhausted outside a system as a collection duct 14 with a dust separator 2 installed on an after stream of the desulfurizing apparatus 3. Further, when elimination of halogen gas components is required, the outlet gas of the dust separator 2 is eliminated with a halogen adsorbent 15 in a halogen eliminator 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a halogen or alkali contained in a high-temperature reducing gasified gas obtained by gasifying coal, heavy oil, or the like, for use as a fuel for an integrated power generation system or a fuel cell. The present invention relates to a method for dry-absorbing and removing trace substances such as metals and heavy metals.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of suppressing a rise in the price of clean fuel, technology for utilizing inexpensive coal or heavy oil has been developed. The method of using it as fuel for a battery or a raw material for chemical synthesis is a typical example. This gasification gas varies depending on the raw material coal and heavy oil, but several tens to several thousand ppm
In addition to sulfur compounds such as H ₂ S and COS, and unburned carbon (char), trace components such as tar and ammonia (N
H ₃ ), cyanide (CN) compounds, halogen gas components (Cl, F
Hydrogen halide or halogen), alkali metal (N
a, K, etc.) Compounds and heavy metals (As, Cd, Hg, Pb, Zn, etc.)
And its compounds, it is necessary to remove harmful components in order to prevent corrosion or pollution of downstream equipment such as gas turbines.

[0003] There are a wet method and a dry method for removing sulfur compounds, but the dry method is advantageous for gasification gas from the viewpoint of thermal efficiency. As a type of the apparatus used in the dry method, there are a fluidized bed system in which a desulfurizing agent is absorbed and reacted in a fluidized state, a moving bed system in which an absorption reaction is performed while moving, and a fixed bed system.
When the transport of the desulfurizing agent is carried out under pressure, the tanks and pipes are worn, which causes a problem in the long-term reliability of the apparatus. Accordingly, the present inventors have been developing a fixed bed gas purification technology for combined gasification gas such as coal using a fixed bed system. And various proposals regarding the desulfurization method, desulfurization tower and desulfurizing agent have been made.

[0004] The state of the art will be described below based on these techniques. FIG. 1 is an example of a system configuration of a fixed-bed gas purifier. The fixed-bed gas purifier includes a dust collector 2 for removing dust in the gasified gas 1, a desulfurizer 3 for removing sulfur compounds, and a collector 4 for collecting the removed sulfur as single sulfur or gypsum. You. Various trace substances that have become gaseous in the high temperature atmosphere (1200 to 2000 ° C) of the gasifier main body are partially unburned carbon (chamber) before being cooled to the inlet gas temperature of 400 to 450 ° C. -), Ash or tar is condensed and collected on the solid surface, but mostly flows into the gas purifier in gaseous form. The temperature of the gasified gas 1 at the inlet of the dust collecting device 2 is 400 to 450 ° C., the pressure is about 24 to 26 atm, and the gas is introduced into the dust collecting device 2 equipped with a ceramic porous filter. Is collected and collected on the filter and discharged out of the system as collected dust 5.

[0005] Desulfurizer 3 installed downstream of dust collector 2
In the reaction tower (two shown in the figure), iron oxide (Fe ₂ O
₃ ) Honeycomb desulfurizing agent containing as a main component is filled.
Iron oxide (Fe ₂ O ₃ ) absorbs sulfur compounds such as H ₂ S and COS in gasification gas 1 at a gas temperature of 400 to 500 ° C.
S), and before the concentration of the sulfur compound in the purified gas 6 at the outlet of the reaction tower reaches the set value, the valve is switched to ventilate the inlet gas to the other reaction tower, so that the gasified gas can be continuously removed. The purified gas 6 is supplied to a downstream gas turbine. On the other hand, the desulfurizing agent that has absorbed the sulfur compound is regenerated under heating with a regenerating gas containing O ₂ and is used repeatedly. Desulfurization and regeneration with iron oxide (Fe ₂ O ₃ ) are represented by the following chemical reaction formula.

[0006]

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[0007]

Embedded image Sulfurous gas (SO ₂ ) 7 generated by regeneration is supplied to a sulfur recovery unit 4
And recovered as elemental sulfur or gypsum 8.

The present inventors have made various proposals regarding a honeycomb desulfurization apparatus and a desulfurization agent, and have found practical use of a desulfurization agent containing titanium oxide (TiO ₂ ) and iron oxide (Fe ₂ O ₃ ) as main components. Was. However, this desulfurizing agent adsorbs and removes sulfur compounds, and contains gaseous alkali metal (Na, K) compounds, halogens (Cl, F) or their compounds, and cyan (CN) contained in coal gasification gas. Compounds, heavy metals (As, Cd, H
g, Pb, Zn, etc.) and ammonia (NH ₃ ) are basically not provided, and some of them do not often meet the fuel standards of gas turbines in downstream equipment. I was seen.

[0009]

SUMMARY OF THE INVENTION The present invention is intended to remove dust and sulfur compounds in the gasification gas of coal and heavy oil, and at the same time, to cause a gas turbine of a downstream device to corrode or to regulate the concentration in the atmosphere. Gaseous alkali metal (Na, K) compounds and halogen gas components (C
l, F and other hydrogen halides and halogens), heavy metals (As,
Cd, Hg, Pb, Zn, etc.) and its compounds, trace substances such as ammonia, especially halogen gas components, trace substances such as ammonia without lowering the gas temperature, that is, the feature of the dry method that is excellent in thermal efficiency. It is an object of the present invention to provide a method of removing trace substances for producing a gasified gas which meets the fuel specifications of a gas turbine by effectively removing it without losing it.

[0010]

Means for Solving the Problems In dry-refining and removing dust and sulfur compounds contained in a high-temperature reducing gas, the present inventors have a desulfurization apparatus for removing sulfur compounds and a dust collector for removing dust that flows downstream. Between the devices, ammonia and halogen gas components react to form ammonium salts; add a basic inorganic compound such as calcium hydroxide to absorb and remove halogen gas components; By installing a remover, and reheating the purified gas at the outlet of the dust collector with a heat exchanger for gas heating and exchanging heat with a heat medium between both heat exchangers, trace substances in the high-temperature reducing gas are reduced. The present inventors have found that dry removal can be performed with good thermal efficiency and completed the present invention.

That is, a first aspect of the present invention is a method for dry refining and removing dust and sulfur compounds contained in a gasified gas obtained at a high temperature, wherein a dust collecting step is provided downstream of the desulfurizing step. After reacting the halogen gas component in the gasified gas after desulfurization with ammonia during the dusting process, the gasified gas is cooled and cooled to precipitate ammonium halide, thereby separating the gasified gas. The present invention relates to a method for removing a trace substance, and it is possible to lower the Cl concentration (in terms of hydrogen chloride) to about 20 ppm or less by cooling to 200 ° C. or less. The second aspect of the present invention is to provide a gasified gas after precipitation and separation of ammonium halide,
Calcium hydroxide, calcium oxide, calcium carbonate,
Adding a basic inorganic compound selected from the group consisting of sodium carbonate, sodium hydrogen carbonate, sodium hydroxide and a mixture thereof to react and separate the halogen gas component in the gasified gas with the basic inorganic compound The present invention relates to a method for removing a trace substance from a gasified gas of the present invention, and the temperature at which a basic inorganic compound is reacted with Ca (OH) ₂ by using 2 to 3 times the halogen gas component as a basic inorganic compound. At 240 ° C, the Cl concentration in the gasified gas is 100pp
It decreased from m to 7 ppm, and decreased from 20 ppm to 0.5 ppm at 200 ° C. The third aspect of the present invention is to treat a gasified gas after reacting and separating a halogen gas component with a basic inorganic compound with a halogen adsorbent selected from the group consisting of zeolite, activated alumina, sodium carbonate and a mixture thereof. The present invention relates to a method for removing a trace substance in a gasified gas described above, and as a method for adsorbing and removing a trace amount of a halogen gas component remaining in the gasified gas, a zeolite pellet adsorbent is used at 240 ° C. At 200 ° C., the residual Cl concentration decreased from 7 ppm to 0.05 ppm, and at 200 ° C., decreased from 0.5 ppm to 0.05 ppm. A fourth aspect of the present invention is that the gasified gas after desulfurization is cooled by a gas cooling heat exchanger to a temperature required for precipitating ammonium halide, and the gas after dust collection is cooled by the gas heat exchanger. The method relates to a method for removing trace substances in a gasified gas, wherein the heat exchanger for gas cooling and the heat exchanger for gas heating are heat-exchanged with a heat medium. After the desulfurization treatment of the gasified gas temperature of about 420 ° C at the inlet of the refining unit, it is cooled by a heat exchanger for gas cooling, and cooled to 240 ° C to 380 ° C and 200 ° C by a heat exchanger for gas heating. The cooled one could be reheated to 340 ° C.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is applied to dry gas purification in general regardless of the system, but here, a fixed bed system will be described. The desulfurization by the honeycomb desulfurizer is performed before the dust removal by the dust collector. The iron oxide (Fe
_{Since the 2} O ₃ ) -based honeycomb desulfurizing agent is a dust-free type, the amount of dust is reduced to 100 mg / m ³ N by coarse dust collection such as cyclone in advance.
If it is reduced to such a degree, even a gas containing some dust can be stably operated continuously without clogging. In addition, the temperature of the gas at the outlet of the gasifier is 400 to 500 ° C.
Under the conditions described above, and consideration is given not to poisoning of halogen gas components such as hydrogen chloride (HCl).

[0013] Halogen gas components such as hydrogen chloride (HCl) react with excess ammonia (NH ₃ ) in the gasification gas to form solid ammonium chloride (NH ₄ Cl), thereby remaining in trace amounts. Cl can be removed by an absorption reaction with a basic inorganic compound. For example, hydrogen chloride (HCl) and ammonia (NH ₃ ) do not produce ammonium chloride (NH ₄ Cl) in a high-temperature gas of 400 to 500 ° C., and exist in gaseous form, respectively. Then, solid ammonium chloride (NH ₄ Cl) is produced by the reaction of the formula (3).

[0014]

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The concentration of hydrogen chloride (HCl) and ammonia (NH ₃ ) in the gas becomes lower as the gas temperature becomes lower.
At 160 ° C, most of the hydrogen chloride (HCl) reacts and no longer exists in gaseous form. Gas-as a means to lower gas temperature
A gas heat exchanger is used. It is to be noted that it is not preferable to lower the gas temperature too much from the viewpoint of heat utilization. Therefore, the cooling temperature of the gas is determined in consideration of the halogen compound removal rate. Normally, the gasification gas of coal and heavy oil has an ammonia (NH ₃ ) concentration higher than the hydrogen chloride (HCl) concentration, but when the hydrogen chloride (HCl) concentration is conversely high or the gas temperature is only up to about 200 ° C If it does not decrease, use ammonium chloride (NH ₄ C
It is not enough to simply remove the halogen by the formation of l), and it is necessary to remove the halogen gas component by adding a basic inorganic compound. When the ammonia (NH ₃ ) concentration is lower than the hydrogen chloride (HCl) concentration, ammonia may be added.

Examples of the basic inorganic compound include Ca (OH) ₂ and N
a ₂ CO ₃ and the like are known, the former preferably is reacted at 250 ° C. or less, the latter react at 400 to 600 ° C.. The gas temperature at the inlet of the desulfurization step is about 400 to 450 ° C. In the latter case, the gas can be added to the flue as it is.
It needs to be added after cooling to about ° C. Therefore, the temperature at which Ca (OH) ₂ or the like is added is suitably the temperature of the gasified gas cooled to precipitate ammonium chloride. Ca (OH) ₂ or in addition to CaO of Na ₂ CO _3, CaCO _3, etc., NaOH, NaHCO
₃ etc. can be used.

[0017]

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[0018]

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These basic inorganic compounds are used as a dechlorinating agent for waste gas from incinerators as slurry.
The halogen gas component can be supplied in the form of a gas or can be made porous to increase the gas adsorption area and charged into another reactor to remove the halogen gas component.

The reaction product with the basic inorganic compound and the unreacted basic inorganic compound are collected by a dust collector together with the dust component and discharged to the outside of the system.

The trace amount of halogen gas components that could not be collected by the dust collector are further removed by adsorption with a halogen adsorbent filled in a halogen remover, if necessary. As the halogen adsorbent, zeolite, activated alumina, active Na ₂ CO ₃ or the like formed into pellets or the like is preferable.

When the gasified gas is cooled in order to precipitate ammonium halide, it is desirable to reheat the gasified gas after removing the halogen gas component and supply it to the downstream gas turbine. By circulating a heat medium between the heat exchanger and the heat exchanger, the cooled heat can be effectively used as a heat source for heating. A conventional heating medium can be used.

[0023]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples.

(Embodiment 1) A system configuration of a fixed bed type gas purifying apparatus according to an embodiment of the present invention will be described with reference to FIG. 2. However, the present invention is also applicable to a fluidized bed type and a moving bed type. . The pressure of the gasified gas 1 at the inlet of the dry gas purifier is 25 atm and the temperature is about 420 ° C. First, a desulfurization apparatus 3 (here, two reaction towers are provided and switched, provided with a honeycomb desulfurizing agent for removing sulfur compounds) Although an example of use is shown, three or more groups may be provided). Sulfur compounds H ₂ S and COS
Total content varies depending on coal type and gasifier type,
H ₂ S and COS are absorbed and removed by the honeycomb desulfurizing agent. In the present embodiment, the desulfurizing agent filling amount is set such that the switching time of the two reaction towers of the desulfurizing apparatus 3 is set to 4 hours, and the sulfur compound concentration in the purified gas 6 becomes 35 ppm or less. The GHSV (gas hourly space velocity) value was 1,800 h ^-1 . The desulfurizing agent used for desulfurization is obtained by converting the sulfurous acid gas 7 generated by the regeneration treatment into simple sulfur by a gas reduction method in the sulfur recovery device 4, or
It is recovered as sulfur or gypsum 8 instead of gypsum by reaction with CaCO ₃ .

A small amount of ammonia (N
H ₃ ), halogen gas components (HCl, HF, halogen, etc.), cyanide (CN) compounds, alkali metal (Na, K) compounds, and heavy metals (As, Cd, Hg, Pb, Zn, etc.) and their compounds For example, the halogen gas component is HCl
About 10 to 100 ppm in terms of conversion (similar display), and about 500 to 1,500 ppm of ammonia (NH ₃ ). When removing using a reaction (formula (3)) in which solid ammonium chloride (NH ₄ Cl) is precipitated, in order to remove as much as possible the halogen gas component, the gaseous gas in the outlet of the desulfurization unit 3 is used.
The test was carried out under the condition that HCl was 100 ppm and NH ₃ was 1,500 ppm. After the desulfurization, the gasified gas was passed through a gas cooling heat exchanger 9 and cooled to 240 ° C. and 180 ° C. Table 1 shows the results of sampling the purified gas after cooling and analyzing the HCl concentration.

[0026]

[Table 1]

The residual HCl concentration in the gasified gas cooled to 240 ° C. was 100 ppm, which is the same as the gas before cooling, but when cooled to 180 ° C., the residual HCl concentration in the purified gas was reduced to 2.3 ppm, and was approximately 98 ppm. HCl was removed. 240 from these results
It was found that solid ammonium chloride (NH ₄ Cl) was not generated at ° C, but solid ammonium chloride was generated at 180 ° C and separated from the gasified gas. In equation (3)
The equilibrium constant (Kp) of HCl is 2.494 × 10 ^-6 at 180 ° C, 200 ° C
Is 16.95 × 10 ^-6 and 486.4 × 10 ^-6 at 240 ° C (Source: Handbook: Thermodynamic properties of substances, issuance office; Japan-Soviet News Agency, Showa 54)
November 5). From this, the pressure 25 atm, NH ₃ concentration 1,500ppm
Calculating the HCl equilibrium gas concentration of the ammonium chloride formation reaction under the conditions of 2.7 ppm at 180 ° C and 18.1 pp at 200 ° C
m, 518 ppm at 240 ° C, which is in good agreement with the analytical value.
That is, in this case, when the halogen gas component is regarded as HCl, 240
At 100 ° C, since the HCl concentration of 100 ppm is below the HCl equilibrium gas concentration, ammonium chloride formation reaction does not occur, but 180 ° C.
Since the HCl equilibrium gas concentration is much higher than 2.7 pppm, it can be determined that the difference is precipitated as solid ammonium chloride. Also, since the HCl equilibrium gas concentration at 200 ° C is calculated to be 18.1 ppm, several ppm can be obtained by cooling to about 180 to 200 ° C.
It is possible to reduce the concentration of HCl to about 20 ppm.

Another method for removing halogen gas components is a method using Ca (OH) ₂ as a basic inorganic compound. In the desulfurized gas treated in the desulfurization device 3, Ca (OH) ₂ as a basic inorganic compound 13 is added in a molar ratio of 2 to HCl with respect to HCl.
When three times the amount is added, HCl in the gasified gas is fixed as CaCl ₂ by the reaction of equation (4). At this time, halogen gas components such as HF are also fixed as CaF ₂ . The reaction of the formula (4) is preferably performed at 250 ° C. or lower, and the reaction was carried out at a gas temperature of 240 ° C. or 200 ° C. Although Ca (OH) ₂ was sprayed into the gas in powder form by the basic inorganic compound supply device 16, the gas temperature dropped by about 40 ° C. due to evaporation of attached water and the like. Thereafter, the gas was cooled to 280 ° C. or 240 ° C. in advance through a gas cooling heat exchanger 9. Assuming that the gasified gas after the precipitation of ammonium halide contains 100 ppm of HCl in the case of a reaction at 240 ° C. (that is, no ammonium chloride is precipitated) and that of 20 ppm of HCl in the case of a reaction at 200 ° C., OH) ₂ was added in a molar ratio of 2.5 to HCl. The generation of CaCl ₂ mainly occurs in the duct near the Ca (OH) ₂ addition in the duct through which the gasification gas flows, but also partially progresses in the deposition layer on the porous filter element of the dust collector 2 in the downstream. I do.

In the fixed bed system configuration, a desulfurizer is usually installed downstream of the dust collector, but in the present invention, new dust is generated due to the addition and supply of the basic inorganic compound 13. Therefore, it is desirable to install the dust collector 2 downstream of the desulfurizer 3. In the dust collection device 2, the main component
Other than calcium compounds (CaCl ₂ , CaF ₂ , unreacted Ca (O
H) ₂ ) and other trace substances such as alkali metals (Na, K, etc.) and heavy metals (As, Cd, Hg, Pb, Zn, etc.) are fixed and collected, and collected as dust 14 outside the system. Is discharged. The concentration in the outlet gas of the dust collector 2 is 1 mg / m ³ N for dust.
At the reaction temperature of 240 ° C, the inlet gas concentration of 100ppm drops to 7ppm, and at 200 ° C, the concentration of halogen gas component becomes 20ppm.
It decreased to 0.5 ppm. The dust collecting device 2 can use a dust collecting type such as an electric dust collector and a granular bed filter in addition to the porous filter dust collector.

When the halogen gas component needs to be further removed, the outlet gas of the dust collector 2 is led to the halogen remover 17 and removed by the halogen adsorbent 15. Here, a very small amount of halogen gas components that could not be removed by the addition of the basic inorganic compound 13 are adsorbed and removed. In the present embodiment, a zeolite pellet adsorbent (3 mmΦ) was used as the halogen adsorbent 15, and the gasified gas was passed through the halogen remover 17 at an SV value of 3,000 h ⁻¹ . After passing through the halogen remover 17, the concentration of the halogen gas component of the purified gas 6 is set to a reaction temperature of 24.
It was 0.05 ppm at both 0 ° C and 200 ° C, and was almost completely removed.

The outlet gas of the halogen remover 17 is reheated by the gas heat exchanger 10. At this time, the heat medium 11 circulates between the gas-cooling heat exchanger 9 and the gas-heating heat exchanger 10, so that the cooled heat and the heating heat can be used efficiently. The fuel gas 12 thus reheated and supplied as the gas turbine fuel has an outlet gas temperature 240 of the gas cooling heat exchanger 9 even if heat is not supplied from the outside.
To recover to 380 ° C at ℃ and to 340 ° C at 200 ° C,
Removal of trace substances such as halogens can be achieved without significantly losing the high thermal efficiency characteristic of dry gas purification.

The fuel gas 1 to be supplied to the gas turbine
In the case where the temperature of Step 2 can be lowered to 340 ° C. or less, the purified gas 6 and the desulfurized gas are separated by the heat exchanger 9 for gas cooling without using the heat exchanger 10 for heating gas and the heat medium 11. To heat the purified gas 6 by heat exchange.

[0033]

According to the present invention, when high-temperature reducing gas such as coal gasification gas or heavy oil gasification gas is subjected to dry gas purification (degassing and desulfurization), the high thermal efficiency characteristic of dry gas purification is maintained. However, it is possible to make the concentration of the trace substance lower than the standard value of the downstream gas turbine fuel or the required value for reduction from the viewpoint of the regulation of the emission of air into the atmosphere.

[Brief description of the drawings]

FIG. 1 is a diagram showing a system configuration of a conventional fixed-bed gas purifier.

FIG. 2 is a diagram showing a system configuration of a fixed-bed gas purifying apparatus according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gasification gas 2 Dust collection device 3 Desulfurization device 4 Sulfur recovery device 5 Collection dust 6 Purified gas 7 Sulfurous acid gas 8 Sulfur or gypsum 9 Heat exchanger for gas cooling 10 Heat exchanger for gas heating 11 Heat medium 12 Fuel gas 13 Basic inorganic compound 14 Collected dust 15 Halogen adsorbent 16 Basic inorganic compound supply device 17 Halogen remover

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Seiji Kagawa 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Sanishi Heavy Industries, Ltd.

Claims (4)

[Claims] 1. A method for dry refining and removing dust and sulfur compounds contained in a reducing gasified gas obtained at a high temperature, wherein a dust collecting step is provided downstream of the desulfurizing step, and the dust collecting step is performed between the desulfurizing step and the dust collecting step. Removing the trace substances in the gasified gas by reacting the halogen gas component in the gasified gas after desulfurization with ammonia and cooling the gasified gas to precipitate and separate ammonium halide. Method. 2. The gasified gas after precipitation and separation of ammonium halide is selected from the group consisting of calcium hydroxide, calcium oxide, calcium carbonate, sodium carbonate, sodium hydrogencarbonate, sodium hydroxide and mixtures thereof. The method for removing a trace substance in a gasified gas according to claim 1, wherein the added basic inorganic compound is added, and a halogen gas component in the gasified gas is reacted with the basic inorganic compound to be separated. 3. The method according to claim 1, wherein the gasified gas after reacting and separating the halogen gas component with a basic inorganic compound is treated with a halogen adsorbent selected from the group consisting of zeolite, activated alumina, sodium carbonate and a mixture thereof. Item 2
2. The method for removing trace substances in a gasified gas according to item 1. 4. The gasified gas after desulfurization is cooled by a gas cooling heat exchanger to a temperature required for precipitation of ammonium halide, and the gas after dust collection is re-used by the gas heating heat exchanger. The method for removing a trace substance in a gasified gas according to any one of claims 1 to 3, wherein the method comprises heating and exchanging heat between the gas cooling heat exchanger and the gas heating heat exchanger with a heat medium.