CS198230B2 - Method of producing gas having high heating value from raw gas - Google Patents

Abstract

1517140 Purifying producer gas METALLGESELLSCHAFT AG 2 May 1977 [26 May 1976] 18355/77 Heading C5E A solids-laden crude gas at 350-800‹C, which has been produced by gasifying a solid fuel (e.g. coal) under a pressure of 5-150 bars with steam and/or free O 2 , is purified by removing some of the solids in a coarse purification stage (e.g. one or more cyclones) and then scrubbing the gas with a liquid hydrocarbon at 200-300‹C and having a maximum water content of 5 weight per cent, to give a gas having a high calorific value and low dust content. The gas leaving the coarse purification at above 350‹C may be cooled before scrubbing by being sprayed with water. Preferably at least 70% of the hydrocarbon scrubbing liquid has a b.pt. above 350‹C. The scrubbing may be carried out in one or more Venturi-type or radial flow scrubbers. The used scrubbing liquid may be separated into a heavy phase and a lighter phase, the former being recycled to the gasification reactor, and the latter to the scrubber.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for producing a heating gas from a solid gas having a temperature of 250 to 800 ° C containing solids obtained by gasifying solids, especially coal, in a gasification reactor at 5 to 150 bar. free - oxygen as a gasifying substance.

The pressure gasification of solid fuels, in particular hard coal, lignite or peat, has long been known. They are especially '. known details of the pressure gasification method and the corresponding. gasification reactors. or pressure gas generators.

According to known methods, the pressure gasification of solid fuels is carried out with oxygen and water vapor as gasifiers in a fixed bed. Carbon dioxide can also be used as the gasifier. The raw gas is at a temperature in the range of 350 to 800 ° C during gasification, the most important gas components being hydrogen, carbon monoxide and methane.

It is also possible to - gasify - solid fuels. air or oxygen-enriched air mixed with water vapor to obtain so-called weak gases having a low calorific value of 1200 to 2000 kcal / Nm3, based on dry gas. These gases are particularly suitable for heating and - also - in electricity · 2. ......, steamers, for example - in combination - turbines - gas - and steam.

The gases obtained by gasification of solid fuels contain, according to the composition of the gasification substances, nitrogen, water vapor and also - a considerable amount of hydrocarbons of various kinds - and the boiling state, in addition ammonia and - also sulfur compounds. - In the raw gas - there are also dust to fine grains, - simultaneous entrained solid particles of fuel and / or ash. The content of dust or fine-grained solids - in the raw gas depends to a large extent on - load - of the gasification reactor, on the fuel behavior during · - - gasification - and on the fine-grained proportion - of - the fuel to be burned. - Developments to higher gas generator capacities have also led to higher ejection of fine-grained solids with raw gas. The dust content of the raw gas often exceeds - 10 g / Nm ⁵ -,. so, the use of this gas - for example in working machines was not possible without thorough dust removal.

It is an object of the present invention to prepare from the raw gas, under pressure gasification of solid fuels, a heating gas with a minimum dust content.

According to the invention, the process for producing low-calorific calorific gas consists in that the hot raw gas is partially freed from the solids in the coarse scrubbing stage and is brought into contact with a scrubbing liquid consisting of a hydrocarbon and not more than 5% by weight. % water having a temperature of 200 to 300 ° C in an amount of 0.5 to 6 liters per Nm ^{3 of the} raw gas, the hydrocarbon scrubbing liquids having at least 70% boiling point above 350 ° C, and a calorific gas In a rapid scrubbing step, the gas is purged practically only with the hydrocarbons which in part evaporate into the gas, thereby increasing the 'calorific value' of the gas to be purged into the gas. dust-free ... condition.

Surprisingly, the use of hydrocarbons as a scrubber also reduces the residual solids content of the scrubbing gas to the values required in machine operation without using a significant amount of water. If water was used as a detergent in the quick-wash stage, too much water vapor would enter the scrubbed gas, which would greatly reduce its calorific value.

For the process according to the invention, it is expedient that the washing liquid for the quick-washing step comprises at most 2% by weight. % water. Preferably, the carbohydrate hydrocarbons have a boiling point above 350 ° C, in particular at least 85%.

For the quick wash step. at least one Venturi or radial flow scrubber is used. In particular, a scrubber with radial flow ensures a 'low content' of dust in the scrubbed gas. In the coarse scrubbing stage, which is preceded by the quick scrubbing stage, the raw gas is preferably passed through at least one cyclone while at the same time dry-removing the major portion of the coarse-grained solids.

Low-dust calorific gas is used in power plants to propel gas and / or steam turbines.

The method of the invention is explained in more detail in FIG. exemplary. The embodiment shown in the attached diagram.

In the known gasification reactor 1, the granular, solid fuel supplied by line 2 is degassed at a pressure of 55. to. 150 - bars in still. loži. The gasification is effected by supplying oxygen and defective steam through line 3, wherein the oxygen can be replaced in whole or in part by air. The ash is removed from the gasification reactor 1 via line 4.

The crude gas obtained by gasification is continuous from odvádí- - zpiynovacího reactor 1 with a temperature - from 350 to 80Q ° ^C and flows via line 5 to a cyclone evaporator

6. The separated solids are collected in line 7a. if the proportion of fuel in the solids in the pipe - 7a is reasonably large, it can be recirculated - in an unspecified manner to the - gasification reactor 1.

From the dust cyclone 6, the raw gas flows through line 7 to the quick-wash stage indicated in the diagram by a radial-flow scrubber 8. if the gas temperatures at the outlet of the dedusting cyclone-6 are above 350 ° C, it is preferable to cool the gas before entering the quick-wash stage, which is most easily accomplished by injecting water in the cooler 9 provided with a water supply line 10 and a discharge line 11. Cooling prevents the scrubbing of the scrubbing liquid components - when encountering the hot pre-cleaned gas in the scrubber 8.

In a radial flow scrubber 8, the gas is sprayed with the scrubbing liquid from the manifold 12. Usually, the consumption of the scrubbing liquid is 0.5 to 6 liters per 1 Nm5. The scrubbing liquid is supplied via line 13. In the radial flow scrubber 8, there is a high relative velocity between the flowing gas and the droplets of the scrubbing liquid, which leads to a relatively high probability of sprinkling for dust particles.

as mentioned, the scrubbing liquid almost entirely consists of the hydrocarbons obtained from the gasification contained in the raw gas. The temperature of the washing liquid is preferably 150 to 350 ° C, most preferably 200 to 300 ° C. The lower temperature limit is chosen to be higher than the temperature of the saturated steam - gas - contained in the water vapor and - to avoid - condensation.

In the scrubber 8, the scrubbed gas, together with the scrubbing liquid, passes through a circular gap 14 of variable width and flows then to the outside and down along the bell-shaped guide body 15. The gas flow path in the scrubber 8 is indicated by dashed lines 17, 18 .

The mixture of gas and detergent is passed from the scrubber 8 via a line 20 to the waste heat boiler 21, where it is cooled by indirect heat exchange. The heavy hydrocarbons - contained in - also condense in the gas. The cooling is adjusted so that water vapor does not condense at all or only slightly in the waste heat boiler 21. The sludge 21a of the waste heat boiler 21 can be designed as a cyclone separator in order to achieve a good separation of the purified gas and the solid-enriched liquid. The cooled hydrocarbon-containing gas - with a lower boiling point - is discharged from the boiler 21 to the waste heat by withdrawing 22 of the pure gas. The solids content of the gas is not more than 10 mg / N @ 3. Before this pure gas is used as a high calorific value, it may be useful to trap hydrocarbon droplets in an unmarked trap.

The cooled detergent flows from the waste heat boiler 21 to the tar separator 23 where the various hydrocarbons are separated in a known manner according to the gravitational principle. Together with the solids, the heavy hydrocarbon fraction - is collected - at the lower end of the tar separator - 23 and is drawn off via line 24 via a pump 25.

26. Mixer 27 at the bottom of the separator 23

198 tar provides an even distribution of solids in the liquid phase. '

The lighter hydrocarbon fraction present in the tar separator 23, which contains only a small proportion of solids, is discharged via line 13 via pump 28 back to the scrubber 8.

In the waste heat boiler 21, water vapor is generated by indirect heat exchange for gasification in the reactor 1 and for this purpose water is supplied via line 30. The resulting water vapor is transferred via line 31 to line 3. for gasification substances. The oxygen-containing gas and optionally additional water vapor is supplied via line 32.

Example

Schematically indicated. about 48,000 Nm @ 3 / h of dry-gas at a pressure of 20 bar is produced in a pressure gasification reactor 1 of known construction (pressure gasification generator LURGI). For the production of this gas, 17,000 kg of granular hard coal and about 25,000 Nm ^{3 of} air are introduced into the reactor 1 per hour with a steam addition of 0.35 kg / Nm ⁵ . The dry gas exiting pipe 5 has the following composition:

CO ₂ + H ₂ S 14.4% vol

H2 22.7% vol.

N2 41,0% vol

CO 17.1% vol

CH4 4,2% vol

C _n Hm 0,6 vol θ / ο

Relationship. to dry raw gas, the following proportions are still contained in the gas produced:

tar and oil 40 g / Nm ³ gasoline gas 7 g / Nm ³ water vapor 0.14 kg / Nm ³ dusty solids 8 g / Nm ³

The lower calorific value of the raw gas is about 1690 kcal / Nm ³ . Raw gas temperatures

Claims (8)

SUBJECT CLAIMS 1. A method for producing a heating gas from a crude gas having a temperature of 250 to 800 ° C containing solids obtained by gasifying solids, in particular coal, in a gasification reactor at a pressure of 5 to 150 bar with water vapor - and free oxygen-containing gases. as a gasifier, characterized in that the hot crude gas is partially freed from the solids in the coarse scrubbing stage and is contacted with a scrubbing liquid consisting of hydrocarbons and at most 5% by weight of water at a temperature of 200 to 300 ° C in the amount of 0.5 to 6 liters of Nm ^{3 of the} raw gas, while the hydrocarbons of the scrubbing liquid 30 in the pipe 5 fluctuate -between. 520-550 ° C. The raw gas flows through a dedusting cyclone 6 and, in the cooler 9, is cooled to 350 ° C by blasting water vapor. The water vapor content of the gas is thereby increased to 0.27 kg / Nm 3 - dry gas. In a radial-flow scrubber 8, the gas is subjected to a rapid scrubbing process while spraying with an amount of about 25 m ³ / h of the tar liquid circulated. - The washing liquid contains about 85% of hydrocarbons with a boiling point above 350 ° C. The clean gas exiting the scrubber 8 comprises. - - in addition to unchanged - gas fractions, 0.27 kg / Nm ^{3 of} water vapor, 7 g / Nm ^{3 of} gasoline from gas and 47 g / Nm ^{3 of} tar and oil, based on dry gas. Lower calorific value - moist. gas is about 1600 kcal / Nm ³ . The gas and scrubbing liquid are transferred from the quick scrubber stage to the waste heat boiler 21, where part of the free heat is converted by indirect heat exchange to 4200 kg / h of high pressure steam at a pressure of 25 bar. Advantageously, this steam can be directly mixed as gasification steam into the gasification air without additional compression and introduced into the gasification reactor L - for gasification - a total of 8750 kg / h of water vapor is needed, of which - 4000 kg / h it comes from the known water cooling of the gasifier reactor jacket 1,400 kg / h is obtained in the waste heat boiler 21 and the remainder of about 550 kg / h is taken from a foreign steam source. In the waste heat boiler 21, the pure gas is cooled to 225 ° C. Since the dew point of water vapor in pure gas is 158 ° C,. the gas temperature is sufficiently high to avoid - condensation of water vapor. Wash liquid, thickened as a result of evaporation of more easily boiling fractions, flows from the waste heat boiler sludge tank 21a into the tar separator 23. There, according to the gravitational principle, a heavy phase containing a large proportion of solids and a lighter phase with a low solids content are separated. If the gas - in contrast to the aforementioned - raw gas was scrubbed with water, we would obtain pure gas with a lower calorific value of only 1120 kcal / Nm ³ . YNALEZU in a 70% proportion - boiling point above - 350 ° C, and - the heating gas is - drawn off with a dust content - not more than 10 mg per Nm ³ . 2. Method according to claim 1, characterized in that the scrubbing liquid for the quick wash step comprises at most 2% by weight of water. % water. 3. Process according to claim 1, characterized in that - the hydrocarbons of the washing liquids have a boiling point above-350 DEG C., in particular at least 85%. 4. - The process according to claims 1 to 3, characterized in that the coarse cleaning step consists of at least one cyclone. 5. Method according to any one of claims 1 to 4, characterized in that the quick-washing stage consists of at least one Venturlho washing machine or a radial flow washing machine. 6. A process as claimed in any one of Claims 1 to 5, characterized in that the raw gas is cooled before it is introduced into the rapid scrubbing stage when the raw gas is discharged from the coarse scrubbing stage above 350 [deg.] C. 7. A method according to any one of claims 1 to 6, wherein the gas, after leaving the quick scrubbing stage, is cooled together with at least a portion of the scrubbing liquid by indirect heat exchange. 8. A method according to any one of claims 1 to 7, characterized in that the lighter, low solids tar separator phase is reused as a washing liquid in a quick wash step. \