WO1986000920A1

WO1986000920A1 - Process for the removal of volatile contents from water produced during coal upgrading processes

Info

Publication number: WO1986000920A1
Application number: PCT/EP1985/000297
Authority: WO
Inventors: Georg Pollert
Original assignee: Bergwerksverband Gmbh
Priority date: 1984-07-19
Filing date: 1985-06-19
Publication date: 1986-02-13
Also published as: JPS61502764A; DE3426562A1

Abstract

In a process for the removal of volatile contents from the water produced during coal upgrading process, gas is heated in a direct heat exchanger (9), saturated with steam and then used in order to drive out the volatile substances in a stripper (4). The liquid which is fed into the direct heat exchanger is pre-heated in one or several indirect heat exchangers (17, 36), with partial or total use of the heat which is given off.

Description

Process for the removal of volatile constituents from water from coal refining processes

The invention relates to a method for removing volatile ingredients such. B. ammonia, sulfur hydrogen and hydrocyanic acid from waters of coal refining plants with a hot gas stream in a stripper.

In the processing of coal, such as gasification, Verflüssi¬ supply or coking, fall through the generally at introduced into the process carbon humidity as well as by ^'during the process prior to continuous chemical transformations water to the inorganic by the organic and non-volatile and volatile contain inorganic substances such as ammonia, hydrogen sulfide and hydrocyanic acid. These volatile inorganic compounds must be largely removed from the water before they are returned to the process as wash water or - usually after another treatment act to remove or reduce the other harmful ingredients - as wastewater.

In the same way, wash water and steam condensates enriched with volatile substances must be treated. The removal of the volatile inorganic constituents from such waters is carried out on coal upgrading plants practically exclusively in abrasives which are operated with steam as the heating and carrier medium. As a result, water enters the process as steam condensate.

This steam is a high cost factor, particularly because of the sharp rise in energy costs in the past few years, and has a considerable impact on the economy of coal refining plants. When steam is used to strip the process water, in addition to the costs for its presentation, there are also costs and environmental pollution due to the increase in the amount of waste water and cooling.

It is known that volatile constituents can also be stripped from water laden with such water with gaseous media other than water vapor. Suggestions in this regard have been made several times for coking water. For example, British Patent No. 1,181,587 suggests treating ammonia water laden with pollutants with lean gas in a stripper and passing the loaded gas into the underfiring of the coke ovens, the ammonia in the regenerator due to the high temperature of 1200 ° C is thermally split into nitrogen and hydrogen. In order to achieve a good stripping effect, very large gas-liquid ratios are necessary in this process because of the relatively low temperature. In addition, according to Grosskinsky, "Handbuch des Kokereiwesens", Karl Knapp-Verlag, Düsseldorf, 1958, Vol. II pp. 258/59, a temperature of at least 65 ° C is necessary in order to remove the compounds present in the ammonia water, for example Ammonium carbo- completely dissociate nate or ammonium sulfide. If you now operate such a stripper with a preheated gas and an ammonia water of the same temperature, the water will evaporate until the gas is saturated with water vapor. However, due to the high heat of vaporization of water, this leads to a strong cooling in the system. If you want to perform such a stripping process at 70 ° C and calculate with a gas-condensate ratio of 500 m ³ i. N. to 1 ³ , then a heat of vaporization of approx. 400,000 kJ per m ^{3 of} water to be stripped corresponds to a gas throughput of 500 m ³ i. N. required. This quantity of heat has to be supplied predominantly from the outside by heating the gas, since preheating the ammonia water to over 80 ° C raises technical problems and the temperature difference between 80 and 70 ° C of the ammonia water offers just 10% of the required quantity of heat . The necessary heat must therefore be

3 are brought. To do this, the gas (c _ value approx. 1.4 kJ / i.

. He N. and K) are preheated to approx. 600 ° C. This makes the use of high quality energy necessary.

A method is also known in which steam is supplied to a stripping gas (US Pat. No. 3,754,376). This procedure has no advantage over stripping with pure steam, since the steam requirement is not significantly reduced.

In DE-OS 14 44 972, the proposal is made to strip water from the template circuit of a coking plant with an inert gas or air, flue gas, water vapor or a mixture of these media in order to remove ammonia and phenols.

The stripping gas is preheated by indirect heat exchange. In addition, water vapor must be added to the stripping gas in order to avoid excessive cooling of the gas and thus a deterioration in the stripping effect. Also here, as with the other processes, it is necessary to add high-quality energy.

Accordingly, the object of the invention is to provide the gas used for stripping as inexpensively as possible.

This object is achieved by a method with the features according to claim 1. Further refinements and improvements are made in accordance with the features of the subclaims.

In the method according to the invention, the steam necessary for the processing of the process water can be partially or completely saved by treating the water loaded with the volatile compounds in a gas stripper instead of in an abortive device, the stripping gas being previously in a di right heat exchanger is heated and saturated with water vapor.

The operating temperature of the stripper is between 65 and

90 ° C, preferably between 75 and 80 ° C and the ratio

3 from gas to liquid between about 100 and 1000 m (in general, dry) to 1 m 3, preferably between 150 and 400 m3 (in general

3rd

N., dry) to 1 m.

The mode of operation of the method according to the invention is described in more detail with reference to the figure and the examples:

example 1

The water from the supply circuit of a coke oven battery, which is to be worked up in the stripper, contains 3.7 g NH./1, 0.73 g H ^ S / 1 and 35 mg HCN / 1 of volatile substances to be removed. There will be 25 m ³ / h of this template water 75 ° C through the lines 1, 2 and 3 to the head of the stripper 4. At the foot of the stripper 4, the purified water runs through lines 5 and 6. It still has a concentration of volatile ammonia of 72 mg / 1, of hydrogen sulfide of less than 1 mg / 1 and of hydrocyanic acid of 11 mg / 1. In countercurrent, 10,000 m ^{3 of} air at 20 ° C./h are passed with the aid of fans 25 through lines 7 and 8 into the direct heat exchanger 9, which, for. B. is formed as a packed column, heated there to 75 ° C and water vapor saturated with 4.9 t.

This hot, water vapor-saturated air enters through lines 10 and 11 in the foot of the stripper 4, where it strips the template solution entering through line 3 in countercurrent, and leaves the stripper, enriched with the volatile substances, via lines 12 , 13 and 14. 120 m ^{3 of} cooling water per hour are guided in the cooler 17 via the lines 15 and 16. B. could be the pre-cooler of a coking plant, heated there to 78 ° C and given via lines 18, 19, 20, 21 and 22 at 77 ° C to the head of the direct heat exchanger 9. Here, the cooling water is cooled to 50 ° C. by heating and saturating the air conducted in countercurrent and leaves the direct heat exchanger via lines 23 and 24.

The air laden with the stripped volatiles can e.g. B. ge in the underfiring of a coke oven or in the regeneration of an oxidative desulfurization.

The amount of heat required for heating and water vapor saturation can also be obtained elsewhere, such as. B. in the abortion of an ammonium sulfide circuit wash or in the washing oil cooling of a benzene factory. The stripper drain can also be placed entirely or partially in a gas scrubber. Acid can be added beforehand through line 26 in order to bind the remaining volatile ammonia. In this example, 265 g of 78% sulfuric acid are added per m ³ . The stripper drain must be cooled before being placed in a gas wash.

If you compare this mode of operation with the otherwise usual operation of a steam stripper, the economic benefit of the invention becomes clear: the 5 t of steam per hour otherwise required for the stripping of 25 m ^{3 of} template water are saved. All that is necessary is to use the electrical energy for the stripping air, which in the case of a 15-tray stripping column (diameter 2.7 m) and a direct heat exchanger (diameter 2.7 m), which over a height of 6 m Pallring with a diameter of 2.5 cm is loaded, is 30 kWh / h.

The cables and units used here should be thermally insulated in the hot areas.

Example 2

The same liquid as in Example 1 is fed via lines 1 and 27 into heat exchanger 28, where it flows from the stripper outlet, which is fed out again via lines 5 and 29 into heat exchanger 28 and via line 30, to 82 ° C is heated and enters the stripper 4 via the lines 31 and 3. Here it is stripped and heated to 85 ° C. It leaves the stripper with a residual concentration of 61 mg of volatile ammonia, under 1 mg of hydrogen sulfide and 8 mg of hydrocyanic acid per 1. In countercurrent, 5,000 m ³ i. N. Air of 20 ° C / h with blower 25 leads via lines 7 and 8 into the direct heat exchanger 9, which they pass through line 10 at 75 ° C. and steam leaves saturated. 2.85 t of steam are fed in via line 32, so that the air, heated and saturated to 85 ° C., enters the stripper 4 via line 11, which it leaves with the stripped volatile substances via line 12. 60 m ^{3 of} cooling water at 77 ° C. per hour are passed via line 22 to the head of the direct heat exchanger 9, from which the cooling water runs off at 50 ° C. and reaches the indirect heat exchanger 17 via lines 23, 34 and 16 by heating it to 78 ° C. Via lines 18 to 22 it reaches the head of the direct heat exchanger 9 again. The evaporation losses which are removed in the direct heat exchanger 9 by the saturated air are supplemented via line 15. They are approximately 2.5 m ³ / h.

In this mode of operation, 2.15 tons of steam are saved compared to a conventional stripper, while the amount of exhaust air is so small that, for. b. can be completely directed into the regeneration of an oxidative desulfurization process.

Example 3

In a coke oven plant, the gas purification is operated in such a way that the water introduced into the process through coal moisture and formation water (approx. 14% based on the coal used) is not used for washing out ammonia, hydrogen sulfide and hydrocyanic acid or one or two of these substances ¬ can. Here, the entire excess water of the process, to which in addition to the previously mentioned waters, other waters, such as. B. steam condensates come, are stripped by the inventive method.

25 m ³ of water to be cleaned are added to the head of the stripper 4 at 70 ° C. via lines 1 to 3. The salary of the feed water is 4.1 g / 1 for volatile ammonia, 0.98 g / 1 for hydrogen sulfide and 80 mg / 1 for hydrocyanic acid. The water flowing out of the stripper at 80 ° C. has a volatile ammonia content of 50 mg / 1, a hydrogen sulfide content of less than 1 mg / 1 and a hydrocyanic acid content of 20 mg / 1. The outlet of the stripper 4 is led via the lines 5 and 33 into the line 22, in which the 120 m ^{3 of} water coming from line 21 mixes and through which the combined water reaches the direct heat exchanger 9. From this the water runs off at 61 ° C and is fed via lines 23, 34 and 16 into the cooler 17, in which it is heated to 77 ° C. Via lines 18 and 35 it reaches indirect heat exchanger 36, in which it is heated to 83 ° C. It returns to the direct heat exchanger via lines 37, 20, 21 and 22. Since the circuit is continuously fed with 25 m ^{3 of} water / h and 4.8 t of water are withdrawn from the circuit with the stripping gas (see below), 20.2 m ^{3 of} water / h must be drawn off continuously via line 24. The indirect heat exchanger 36, which is switched on in this example in order to achieve a higher temperature level, can also be operated with steam while supplying other energy.

For the operation of the stripper, 7,500 m ³ i. N. cleaned coke oven gas with a residual content of 10 mg ammonia, 120 mg hydrogen sulfide and 30 mg hydrocyanic acid per m ³ i. N. taken from line 38. The gas reaches the direct water vapor saturator 9 via the blower 39 and the lines 40 and 8, where it is heated to 80 ° C., saturated with water vapor and then fed into the stripper 4 via lines 10 and 11.

Here it absorbs the volatile substances from the countercurrent liquid and heats the liquid to 80 ° C, cooling itself to 79 ° C. Then will the gas is returned via lines 12, 13, 41 and 42 to the main raw gas line 43. The combined gas is fed via line 44 into the gas purification 45 and passes via line 38 into line 46, 7,500 m ³ i in turn being fed via the blower 39. N./h be fed back into the stripping cycle. It is also possible to return the gas to the raw gas line before the precoolers. Also, the gas from line 12 may be coming via line 47 to a separate cooler 48 and ^'from there via the lines 49 and 42 in the raw gas Haupt¬ werden- returned 43rd The condensate flowing off via line 50 can be fed in at any point in the coking plant.

According to the example given here, only part of the water to be discharged from the process can also be cleaned, while another part is also used in the gas scrubbing. To chemically bind the residual content of volatile ammonia, acid can be added to the heat exchanger circuit via line 51. The water withdrawn from the heat exchanger circuit via line 24 can be used as wash water for gas cleaning.

The method variant shown in Example 3 has great advantages over a conventional abortion operation. Firstly, about 3.65 are t steam / h is less consumed (if one indirect heat exchanger 45 with steam operates) ^', at the same time a corresponding required for condensing and cooling the vapor amount of cooling water is saved, is on the other of no external water entered in the system in the form of steam condensate, so that correspondingly less waste water is obtained.

The loaded gas from line 14 can also be fed into the underfeed of coke ovens, the calculation shown above showing that compared to British Patent No. 1,181,587 significant progress is being made. In the cited patent an outlet temperature of the stripper of 70 ° C. is given for a good stripping effect. In order to achieve this, the above-mentioned 400,000 kJ must be provided at least per m ³ of water to be stripped, in total 10,000,000 kJ according to the example given here, while only 2,500,000 kJ additional energy in a mode of operation as described here must be used because the remaining necessary energy in the form of waste water is available free of charge.

The additional heat exchanger 36 can also be dispensed with entirely if the stripper 4 is operated at 75 ° C. and the gas to liquid ratio is increased to 400 to 1.

Example 4

A coal liquefaction plant produces 50 m ^{3 of} water per hour, which in addition to various organic impurities contain 10 g of hydrogen sulfide and 30 g of ammonia / 1. This water is added via lines 1, 2 and 3 at 80 ° C. to the top of the stripper 4, from which it is cleaned with a residual content of 80 mg NH 1/1 and below 1 mg H ₂ S 1 above the lines 5 and 6 expire. Via line 8, 15,000 m ³ i. N. inert gas / h with a content of 10 mg NH_ and 80 mg H „S / m ³ i. N. in the direct heat exchanger 9, in which it is heated to 80 ° C. and saturated with water vapor. The gas enters the stripper 4 through the lines 10 and 11, frees the countercurrent water from ammonia and hydrogen sulfide and reaches the gas scrubber 45 in a closed circuit via the insulated lines 12, 13, 41, 42 and 44 , in which it is freed of ammonia and hydrogen sulfide and cooled. From there, it is fed directly via line 38, blower 39 and lines 40 and 8 into the Metauscher 9 returned. This completes the cycle. In countercurrent to the gas, 290 m ^{3 of} cooling water of 82 ° C. are added to the direct heat exchanger 9 per hour, which cool down to 61 ° C. and are fed into the cooler 17 via the lines 23, 34 and 16. There, the water is heated to 83 ° C. and returned to the direct heat exchanger 9 via lines 18 to 22. This cooling water circuit can also be supplied with a stripper drain via line 33.

This process has the decisive advantage over the process principle claimed in American Patent No. 3,754,376 that it can be operated completely without the addition of steam.

Claims

IIPatent claims

Process for the removal of volatile ingredients such. B. ammonia, hydrogen sulfide and hydrocyanic acid from waters of coal refining plants with a hot gas stream in a stripper, characterized in that the gas used for stripping before entering the stripper in a direct heat exchanger and water vapor saturator with water or an aqueous solution is heated and saturated with water vapor, the liquid supplied to the direct heat exchanger being previously heated in one or more indirect heat exchangers with partial or exclusive use of waste heat.

A method according to claim 1, characterized in that the liquid fed to the direct heat exchanger is circulated.

3. The method according to claim 1 and 2, characterized in that the entire stripper drain ^" or a part thereof is fed to the circuit via the direct heat exchanger and a corresponding amount of liquid is withdrawn at another point.

4. The method according to claims 1 to 3, characterized gekenn¬ characterized in that to achieve a higher Temperaturni¬ level the preheated and water vapor-saturated stripping gas is added immediately before entering the stripper steam.

5. The method according to one or more of claims 1 to 4, characterized in that a partial stream of purified product gas is used for the stripping process, which is then returned to the gas cleaning or before the gas cooling.

6. The method according to one or more of claims 1 to 5, characterized in that the operating temperature of the stripper is between 65 and 90 ° C, preferably between 75 and 80 ° C.

7. The method according to one or more of claims 1 to

6, characterized in that the ratio of gas to

3 Liquid between about 100 and 1000 m (in general, dry) to 1 m 3 preferably between 150 and 400 m3 (in general,

3 dry) to 1 m.