JPH09103640A - Method and agent for treating exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas-treating agent for removing acidic substances in exhaust gas which has a high exhaust gas removing effect and does not cause clogging of tanks and piping. SOLUTION: Calcium hydroxide containing 0.05-1.0wt.% of a lower alcohol based on the weight of calcium hydroxide is used as an active component. An agent having a jet index of 60 or more is preferable as an exhaust gas treating agent, and it is preferable for the agent to have pore volume of 0.1cc/g or more and an average pore diameter of 1μm or less and to use ethanol, methanol, or denaturated alcohol as alcohol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to acidic exhaust gas such as sulfur oxides such as sulfurous acid gas, hydrogen halides such as hydrogen chloride and hydrogen fluoride, hydrogen sulfide, etc., and acidic exhaust gas of refuse incinerators and factories. TECHNICAL FIELD The present invention relates to an exhaust gas treating agent, which has a high effect of removing exhaust gas and does not cause clogging of tanks and pipes, and an exhaust gas treating method using the same, which is preferably used as a neutralizing and removing agent for acid waste liquid.

[0002]

2. Description of the Related Art A powdered exhaust gas treating agent is required to have a high gas adsorption efficiency and not be clogged in a tank or a pipe. Of these, calcium hydroxide is used as a neutralizing / removing agent for acidic exhaust gas, but conventional calcium hydroxide has a low reaction activity with SOx and hydrogen halides and has a low exhaust gas removing effect. 2 to 5
It is unavoidable that a large amount of double equivalent is required, and due to the low jetting property, clogging and blockage frequently occur at the bent parts of tanks and pipes, and the pressure of the blower of the continuous exhaust gas treatment agent constant quantity supply device is increased. Since the temperature rises, there is a problem that it is necessary to tap the calcium hydroxide supply pipe to eliminate clogging and blockage.

Therefore, in order to enhance the effect of removing exhaust gas,
A method of using an organic solvent in combination has been proposed (Japanese Patent Publication No.
No. 8194), this method tends to cause clogging or blockage of tanks and pipes, and the obtained calcium hydroxide adheres to the inner walls of tanks and pipes during feeding, transportation and storage, and agglomerates. There is a problem that it does or solidifies. In order to solve such problems as clogging and the like, a method of adding a surfactant in addition to the combined use of an organic solvent has been proposed (JP-A-5-193997),
The cost becomes higher, and in particular, the grade having a good reactivity with exhaust gas generally has a high specific surface area, so that the required amount of the surfactant is increased, and thus the cost is further promoted.

[0004]

Under the circumstances, the present invention has a high exhaust gas absorption efficiency and does not cause the above-mentioned problems such as clogging of tanks and pipes, and an efficiency using the same. The purpose of the present invention is to provide a general exhaust gas treatment method.

[0005]

The inventors of the present invention have conducted various studies to develop an exhaust gas treating agent having the above-mentioned preferable characteristics, and as a result, the calcium hydroxide contains a predetermined amount of a lower alcohol. It has been found that the object can be achieved by using a material having a predetermined physical property, and in particular, the present invention has been completed based on this finding.

That is, in the present invention, the lower alcohol is contained in an amount of 0.05 to 1.0% by weight based on the weight of calcium hydroxide.
An exhaust gas treating agent for removing an acidic substance in exhaust gas, which contains calcium hydroxide as an active ingredient.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Calcium hydroxide, which is an active ingredient of the exhaust gas treating agent of the present invention, is not particularly limited, but those having a jetness index of 60 or more, particularly 63 or more are preferable, and among them, the pore volume is 0. 1 cc / g or more, preferably 0.2
It is preferable that the average pore size is 1 to 5.0 cc / g and the average pore size is 1 μm or less, preferably 0.1 to 0.8 μm. Here, the jet flow index is an index that indicates the likelihood of occurrence of a flushing (scattering) phenomenon, and can be obtained as the total value of the fluidity index, the collapse angle index, the difference angle index, and the dispersity index. Here, the liquidity index is an index for evaluating the difficulty of the outflow due to gravity, and includes the angle of repose index, the compression index,
It can be determined as the sum of the spatula angle index and the uniformity index or the cohesion index. Each of these indices is usually obtained by measuring various physical properties of the powder and granules using a powder tester and converting the measured values into indices according to a predetermined index table. The calcium hydroxide preferably has a specific surface area of 25 m ² / g or more, particularly 30 m ² / g or more. Further, those having an average particle diameter of 6 μm or less, particularly 0.5 to 5.0 μm are preferable. Further, the reaction activity in terms of oxalic acid activity is 30 minutes or less, preferably 10 minutes or less. Here, the average particle size is
Mean cumulative 50% particle size. The oxalic acid activity is
The aqueous suspension of calcium hydroxide prepared as follows was stirred at 550 rpm with a turbine type mixer, and the oxalic acid solution prepared as follows was added to it to measure the time until pH 5 was reached. It was defined as the acid activity.
The above calcium hydroxide aqueous suspension was prepared by adding water to 22.2 g of calcium hydroxide to make 200 g,
It is prepared by stirring at. Further, the oxalic acid solution was prepared by adding water to 25.2 g of oxalic acid dihydrate to obtain 200
g, heated to a solution and prepared at 25 ° C.

When the jet flow index is less than 60, the treatment agent is less likely to be scattered, so that the treatment agent may be accumulated and blocked at a curved portion in the pipe. Pore volume is 0.1
If it is less than cc / g, the exhaust gas absorption efficiency decreases, and if the average pore diameter exceeds 1 μm, air does not reach the inside of the pores of the treatment agent when being supplied by the exhaust gas treatment agent continuous quantitative supply device, so the scattering is insufficient. Therefore, the reactivity with the acidic exhaust gas decreases.

The lower alcohol contained in the calcium hydroxide is preferably one having a boiling point lower than that of water, particularly methanol, ethanol or modified alcohol. As the modified alcohol, commercially available industrial alcohols such as methanol modified ethanol and isopropyl alcohol modified ethanol are preferable. The lower alcohol content is 0.05 to 1.0 based on the weight of calcium hydroxide.
It is necessary that the content is wt%, preferably 0.1 to 0.8 wt%. If the content is less than 0.05% by weight, the tank and piping are likely to be clogged, and even if it exceeds 1.0% by weight, the effect corresponding to the large amount cannot be expected to be improved.

Examples of the exhaust gas treating agent of the present invention include those prepared by mixing one or both of activated carbon and coke with such calcium hydroxide. The amount of activated carbon is 1 to 15% by weight, preferably 3 to 10% by weight, based on calcium hydroxide, and the amount of coke is 1 to 30% by weight, based on calcium hydroxide. ,
It is preferably in the range of 3 to 15% by weight.

The exhaust gas treating agent of the present invention is extremely effectively used for the treatment of various exhaust gases containing various acidic substances for deacidification, especially dehydrohalogenation treatment, especially dehydrochlorination treatment and desulfurization treatment, especially desulfurization gas treatment. Even when the exhaust gas further contains harmful substances such as dioxins, mercury, cadmium, and PCB, the harmful substances can be removed and reduced. In particular, an exhaust gas treating agent containing activated carbon or coke is extremely effectively used for treating the above-mentioned exhaust gas with a deacidifying substance, and can more effectively remove harmful substances such as dioxins, mercury, cadmium and PCB.

The activated carbon is preferably coconut shell activated carbon, coal, or powdered activated carbon based on a wood-based raw material.
The specific surface area is preferably 800 to 1500 m ² / g, and examples of commercially available products include Shirasagi manufactured by Takeda Pharmaceutical Co., Ltd. As coke, lignite coke, especially a specific surface area of 2
It is preferably from 100 to 400 m ² / g.

Further, since the exhaust gas treating agent of the present invention has good fluidity, it is preferably used together with an air flow such as air so as to be in contact with the exhaust gas while being dispersed in the air flow, and particularly used for a dry adsorption system. Even so, it is possible to sufficiently achieve the emission standard of exhaust gas, which was not possible when ordinary slaked lime is used, and brings the advantage of the dry system, that is, the advantage that it can be operated in a dry state and wastewater treatment is unnecessary.

The exhaust gas to be treated is not particularly limited as long as it contains an acidic substance. For example, waste incineration exhaust gas, melting furnace exhaust gas, combustion exhaust gas of fossil fuel in a thermal power plant, and metal refining. Exhaust gas from a combustion device, exhaust gas from various boilers, exhaust gas from a firing device in the ceramic industry, combustion exhaust gas from combustible waste such as old tires, and the like.

The exhaust gas treating agent of the present invention can be produced by digesting dry-milled and classified calcium oxide with a digestive solution consisting of a mixed solution of water and lower alcohol, aging, and evaporating water and lower alcohol. it can. The digestion operation is preferably performed by supplying a mixture obtained by previously mixing calcium oxide and a digestive solution in a mixer and heating the mixture. This heating is preferably carried out by passing heated steam, for example, steam at 100 ° C. or higher, through a jacket attached to the digester. The aging and vaporizing operations are preferably performed together by feeding the digestion reaction product from the digester to the aging machine and heating. This heating is preferably carried out by passing heating steam, for example, steam at 100 ° C. or higher, through a jacket attached to the aging machine.

As calcium oxide used as a raw material in this production method, limestone is usually calcined in a rotary kiln furnace, a Beckenbach furnace, a fluidized-bed roasting furnace, and then crushed by a dry crusher such as a cage mill, a blow mill, a ball mill or a disc mill. And classified with an air filter, a sieve, etc., among which, 20 to 300 μm, preferably 20 to 1
Examples thereof include those having a cumulative 50% average particle diameter of 10 μm. Particularly preferably, the pore volume is 0.1 cc / g or more and the average fineness is the same as that of the preferred active ingredient in calcium hydroxide in the resulting exhaust gas treating agent. The pore diameter is 1 μm or less.

The water in the digestive solution used for digesting the calcium oxide is preferably fresh water, but may contain some impurities as long as the object of the present invention is not impaired, and industrial water is sufficient. is there. The lower alcohol in the digestive juice has a boiling point lower than that of water, especially methanol,
Ethanol and modified alcohol are preferred. As the modified alcohol, commercially available industrial alcohols such as methanol modified ethanol and isopropyl alcohol modified ethanol are preferable.

The weight ratio of water to lower alcohol in the digestive juice is usually 1: 0.8 to 1: 3, preferably 1 :.
It is selected in the range of 1.2 to 1: 2. If there is too much water, the digestive reaction will occur rapidly, and slaked lime will be left in a non-uniform state, and it will not be possible to obtain slaked lime with good reactivity, and if there is too much lower alcohol, the digestive reaction will not occur easily. It takes time to vaporize.

The weight ratio of calcium oxide to water in the digestive juice is usually 1: 0.3 to 1: 2, preferably 1 :.
It is selected in the range of 0.3 to 1: 1.0. If the amount of calcium oxide is too large, some of the calcium oxide will remain in the calcium hydroxide, and if the amount of water is too large, water will remain and aggregate.

It is preferable that the calcium oxide and the digestive solution are well mixed and subjected to a digestion reaction. For example, both are supplied to a mixer at a predetermined ratio and homogeneously mixed in the mixer, and the obtained mixture is usually suspended. It is preferable to supply the suspension to a digester to carry out the digestion reaction. This mixing treatment is usually performed at a temperature of 45 ° C. or lower, preferably 30 ° C. or lower. When the mixing treatment temperature exceeds 45 ° C, a reaction occurs rapidly, the viscosity increases,
Therefore, it becomes difficult to mix them uniformly. Examples of the mixer include a plow blade mixer, a single paddle screw mixer, a double paddle screw mixer and the like.

As the digestion reaction condition, the reaction temperature is usually 7
The reaction time is selected in the range of 0 to 120 ° C., preferably 75 to 110 ° C., and the reaction time of 5 to 180 minutes, preferably 10 to 120 minutes.

The digestion reaction product is then aged, preferably by feeding the digestion reaction product from the digester to the digester. Further, an inert gas and / or dry air is continuously supplied to the aging machine.
As the inert gas, for example, nitrogen, argon or the like is used. The inert gas and / or the dry air is supplied to the aging machine while adjusting the supply amount, the internal temperature of the aging machine and the residence time of the digestion reaction product in the aging machine.

This adjustment is preferably carried out with respect to the amount of inert gas and / or dry air supplied to the aging machine, from 5 to 120 liters, preferably from 10 to 80 liters, per kg of calcium hydroxide in the digestion reaction product. The internal temperature of the aging machine is 70 to 120 ° C, preferably 80 to 110.
℃, the residence time of digestion reaction product in the aging machine is 5
-60 minutes, preferably 10-50 minutes.

In order to maintain the internal temperature of such an aging machine,
It is preferable to fill the jacket attached to the aging machine with heated steam, and in practice, it is practical to pass the heated steam to the jacket.

In this way, water and lower alcohol are vaporized and removed. This treatment is preferably carried out continuously, for example, inert gas and / or dry air is supplied from the lower part of the aging machine, and a filter dust collector such as a bag filter provided in the upper part of the digester and / or the upper part of the aging machine. And the like, and a method of collecting and collecting dust by suction to remove inert gas and / or dry air, water and lower alcohol by suction.

Further, it is preferable to simultaneously purge the inside of the ripening machine with an inert gas and / or dry air supplied into the ripening machine. Further, water and lower alcohol, inert gas and / or dry air sucked by a filter dust collector such as a bag filter and passed through the device are separated into water and lower alcohol and inert gas and / or dry air, It is preferable that water and lower alcohol are reused as a digestive solution, and the inert gas and / or dry air is supplied to the aging machine after passing through an air dryer. The method for producing the exhaust gas treating agent of the present invention has been described in detail above, and one embodiment thereof is shown in a system diagram in FIG.

The present invention also provides a method for treating exhaust gas using this exhaust gas treating agent, that is, an exhaust gas for removing an acidic substance in the exhaust gas by bringing the exhaust gas containing the acidic substance into contact with the exhaust gas treating agent. It also includes a treatment method, and further an exhaust gas treatment method of contacting the waste incineration exhaust gas with the exhaust gas treatment agent to remove at least one selected from dioxin and mercury together with the acidic substance in the exhaust gas. Is.

In this method, the case where waste incineration exhaust gas is used as the exhaust gas will be explained.
A two-step method combining a spray dryer type gas cleaning method and a dry injection method is preferable because it can meet strict emission standards and can reduce the amount of slaked lime used.

When desulfurization is involved, it is preferable to perform a humidification treatment with steam or the like because the effect of collecting sulfur oxides such as SO ₂ is enhanced. At that time, it is preferable to divide the humidification position into two parts, that is, the upstream side and the downstream side of the slaked lime addition position.

[0030]

Next, the present invention will be described in more detail by way of examples, which should not be construed as limiting the present invention. Comparative examples are also shown for comparison with the examples.
Regarding the calcium hydroxide powder obtained in these examples,
The following various measurements and evaluations were performed. Lower alcohol content (wt%): measured using a gas chromatograph (GC10, manufactured by Shimadzu Corporation). Moisture content: Infrared moisture meter (Made by Sebel, METTLER L
P16 + PM400) was used to obtain the sum of water content and lower alcohol content, and the water content was calculated by the following formula. Water content (wt%) = (water content + lower alcohol content)-
Lower alcohol content Pore volume and average pore diameter: Measured using a pore distribution measuring device (manufactured by Shimadzu Corporation, Autopore) by the mercury porosimetry method. Gas absorption rate: 330 mg of the exhaust gas treating agent was added to the odor bag having a volume of 10 liters (manufactured by Omi Odo Air Service Co., Fle
k-Sampler) and the concentration is 1000
10 liters of ppm sulfurous acid gas or hydrogen chloride gas was charged, and after 5 minutes of mixing for 1 minute, the concentration of sulfurous acid gas or hydrogen chloride gas was measured with a gas concentration detector tube (manufactured by Gastec), and the concentration was measured. Taking "C" (ppm), the gas absorption rate was calculated by the following formula. Gas absorption rate (%) = [(1000-C) / 1000] ×
In addition, as the exhaust gas, in Examples 1 to 3 and 5 and Comparative Example 1, a sulfur dioxide gas (nitrogen balance) as a standard gas was used in Example 4
The standard gas used was hydrogen chloride gas (nitrogen balance). Fluidity index and jetability index: Determined using a powder tester (PT-N type, manufactured by Hosokawa Micron).

Example 1 Baking in a Beckenbach furnace, dry crushing in a cage mill,
92 parts by weight of a 60% by weight aqueous ethanol solution was used as a digestive solution for 100 parts by weight of calcium oxide having a pore volume of 0.22 cc / g and an average pore diameter of 0.13 μm, which was prepared by performing air classification. In addition, after mixing with a digester for 15 minutes and mixing at 100 ° C. for 30 minutes at 10 rpm, the mixture is supplied to an aging machine, and heating steam is passed through a jacket to heat the aging machine to 110 ° C. to aging it. While water and ethanol were vaporized, calcium hydroxide powder was obtained. The obtained calcium hydroxide powder has various measurement data shown in Table 1, that is, water content, alcohol content, pore volume, average pore diameter, fluidity index and jetness index, and the gas absorption rate in Table 1 Therefore, it is effective as an exhaust gas treating agent.

Example 2 The same procedure as in Example 1 was repeated except that the mixing treatment in the digester was changed to a treatment in which the mixture was mixed at 60 rpm at 30 ° C. for 15 minutes and then digested at 100 ° C. for 30 minutes in the digester. Operated. The obtained calcium hydroxide powder has various measurement data shown in Table 1 and shows the gas absorption rate in Table 1, and thus is effective as an exhaust gas treating agent.

Example 3 Calcium oxide having a pore volume of 0.27 cc / g and an average pore diameter of 0.18 μm prepared by mercury porosimetry, which was prepared by firing in a rotary kiln furnace, dry pulverization in a cage mill, and air classification. It operated like Example 1 except having used for. Since the obtained calcium hydroxide powder has various measurement data shown in Table 1 and shows the gas absorption rate in Table 1,
It is effective as an exhaust gas treatment agent.

Example 4 Calcium oxide having a pore volume of 0.27 cc / g and an average pore diameter of 0.18 μm prepared by mercury porosimetry, which was prepared by firing in a rotary kiln furnace, dry pulverizing in a cage mill, and air classification. Used in a methanol-modified ethanol with a concentration of 60 wt% (methanol 1 wt%, ethanol 99
(Wt%) Aqueous solution was used in the same manner as in Example 1 except that the digestive fluid was used. Table 1 shows the obtained calcium hydroxide powder.
Since it has various measurement data shown in Table 1 and shows the gas absorption rate in Table 1, it is effective as an exhaust gas treating agent.

Example 5 Pore volume of 0.5 prepared by mercury porosimetry, prepared by firing in a fluidized-bed roasting furnace, dry pulverization in a ball mill, and air classification.
The same operation as in Example 1 was performed except that calcium oxide having 0 cc / g and an average pore diameter of 0.18 μm was used as a raw material.
The obtained calcium hydroxide powder has various measurement data shown in Table 1 and shows the gas absorption rate in Table 1, and thus is effective as an exhaust gas treating agent.

Comparative Example 1 Baking in a Beckenbach furnace, dry crushing in a cage mill,
120 parts by weight of water was added to 100 parts by weight of calcium oxide having a pore volume of 0.22 cc / g and an average pore diameter of 0.13 μm, which was prepared by performing air classification, and the same as in Example 1. Then it was digested and aged. The obtained calcium hydroxide powder has various measurement data shown in Table 1, and shows the gas absorption rate in Table 1.

Comparative Example 2 Commercially available JIS special slaked lime (manufactured by Okutama Kogyo Co., Ltd.) has various measurement data shown in Table 1, and shows the gas absorption rate in Table 1.

[0038]

[Table 1]

From the above, the gas absorption rate is low in the comparative examples in which both the alcohol content rate and the jet flow index deviate from the specified ranges of the present invention, whereas the gas absorption rate in the examples of the present invention is high. It is presumed that the jetting property is good, and therefore no troubles such as adhesion to the inner wall of the tank or piping and clogging of the tank or piping will occur. In fact, as shown in the application examples below, the exhaust gas treatment agent is used during exhaust gas treatment. Since there is no pressure increase in the continuous fixed amount supply device, the above trouble does not occur.

Application Example The exhaust gas treatment during operation of the refuse incinerator with a treatment capacity of 100 tons / day was performed using the exhaust gas treatment agent obtained in Example 2, and the dust collection was performed with a bag filter. The exhaust gas before addition of the exhaust gas treatment agent has a wet gas amount of 30,000 Nm ³ / hr, a dry gas amount of 18,000 Nm ³ / hr, and hydrogen chloride and sulfurous acid gas concentrations of 640 ppm and 5 respectively.
It is 0 ppm, and 50 kg of exhaust gas treating agent is added to this exhaust gas.
It was blown in through a powder continuous quantitative supply device (pipe inner diameter 65 mm, pipe flow rate 15 m / S) at / hr. When the pressure loss of the blower of the powder continuous quantitative feeder at that time was measured, no increase in pressure was observed. The concentration of hydrogen chloride and sulfurous acid gas in the outlet gas after such treatment was drastically reduced to 10 ppm, and the removal rate was 98.4% with hydrogen chloride.
It was 80% with sulfurous acid gas.

Comparative Application Example The same operation as in the application example was performed except that the exhaust gas treating agent was changed to the one obtained in Comparative Example 1. When the pressure loss of the blower of the continuous powder quantitative feeder was measured, a pressure increase of 1500 to 2500 mmAq was observed once every 45 minutes. The concentrations of hydrogen chloride and sulfurous acid gas in the outlet gas after the treatment are 70 ppm and 30 ppm, and the removal rates are 89.0% for hydrogen chloride and 44.4% for sulfurous acid gas, which are the above applications using the exhaust gas treating agent of the present invention. Compared with the case of the example, the frequency of clogging of the exhaust gas treatment agent supply pipe was high, and the effect of removing the acidic exhaust gas was inferior.

[0042]

EFFECT OF THE INVENTION The exhaust gas treating agent of the present invention has a high gas absorptivity, an equivalent effect can be obtained with a smaller amount of use as compared with ordinary slaked lime, a high efficiency of removing acidic substances, and dioxins.
It can remove and reduce harmful substances such as mercury, cadmium, PCB, etc.
The harmful substances can be removed more effectively. Moreover, it has good jet properties and is easy to scatter, therefore, during transportation, during storage or during feeding during exhaust gas treatment, without adhering to the inner wall of the tank or pipe, agglomerating, or solidifying,
Increases the reaction rate with exhaust gas without causing clogging or blockage of tanks and pipes. In particular, those having a large pore volume and a small average pore diameter have remarkable effects as described above. Further, the method of the present invention is suitable for the treatment of exhaust gas containing an acidic substance such as waste incinerator exhaust gas in a refuse incinerator in a city or the like, and combustion exhaust gas of a fossil fuel in a thermal power plant or the like.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of the method of the present invention.

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Claims (10)

[Claims] 1. An exhaust gas treating agent for removing an acidic substance in an exhaust gas, which contains calcium hydroxide containing 0.05 to 1.0% by weight of a lower alcohol based on the weight of calcium hydroxide as an active ingredient. 2. The exhaust gas treating agent according to claim 1, which has a jetness index of 60 or more. 3. The exhaust gas treating agent according to claim 2, which has a pore volume of 0.1 cc / g or more and an average pore diameter of 1 μm or less. 4. The exhaust gas treating agent according to claim 1, 2 or 3, wherein the lower alcohol is at least one selected from ethanol, methanol and modified alcohol. 5. The exhaust gas treating agent according to claim 1, wherein the exhaust gas contains at least one selected from dioxins and mercury. 6. The exhaust gas is a refuse incineration exhaust gas.
The exhaust gas treating agent according to any one of 1 to 5. 7. The composition according to claim 1, wherein the composition is 1 to 15
The exhaust gas treating agent according to claim 5 or 6, wherein the active carbon is blended in a weight percentage. 8. The composition according to claim 1, which is 1 to 30.
The exhaust gas treating agent according to claim 5 or 6, wherein the coke is blended in a weight percentage of 7. 9. An exhaust gas treatment method, which comprises contacting an exhaust gas containing an acidic substance with the exhaust gas treating agent according to claim 1 to remove the acidic substance in the exhaust gas. 10. The waste incineration flue gas according to any one of claims 1 to 8.
An exhaust gas treatment method, which comprises contacting the exhaust gas treatment agent according to any one of 1. to remove at least one selected from dioxin and mercury together with the acidic substance in the exhaust gas.