DE3201526A1 - "QUENCH FOR A COAL GASIFICATION PLANT" - Google Patents

Description

Quench for a coal gasification plant

The invention relates to a quench for a coal gasification plant with a flue dust reactor acting downwards against a water bath. Such a coal gasification plant is known from DE-AS 26 50 512. In detail, the known coal gasification device consists of a vertical reactor with a radiation boiler arranged below it and a lateral branch into a convection boiler. The water bath is located in the foot of the radiation boiler. During operation, synthesis gas is generated from coal, water vapor and oxygen in the reactor. The coal is supplied in the form of coal dust, which is introduced into the reactor from above under the appropriate pressure, so that a downwardly directed cloud of airborne dust is created in the reactor. The individual coal dust particles are converted in the airborne dust cloud at temperatures between 1300 and 1500 ^° C. and a pressure of about 40 bar in the presence of the other gasifying agents to a gas mixture consisting _{of CO and H 2.}

The synthesis gas emerging from the reactor is cooled to a temperature at which the airworthy liquid Slag droplets of the synthesis gas pass into solid slag grains. This happens on the way of the synthesis gas the reactor through the radiation boiler against the water bath. The solidified slag droplets are in the water bath separated from this by diverting the gas flow. According to DS-AS 26 50 512 it is known to use coolants spray into the gas stream exiting the reactor. For this purpose, spray tubes are to be used which are arranged directly below the outlet of the reactor and which enclose the exiting gas stream in a ring.

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This form of quenching is particularly advantageous when the synthesis gas is to be subjected to a subsequent CO conversion. A CO conversion of the synthesis gas is necessary, for example, for the production of methanol, because the raw gas still contains too much CO and too little Hj for the production of methanol.

As a result, in the subsequent CO conversion, a sulfur-resist catalyst is used according to the • Water gas reaction 'converts part of the CO to hydrogen. whereby the same amount of CO ~ is produced. The excess CO2 is then washed out afterwards. With this wash? the sulfur compounds can be removed from the gas at the same time. The gas treated in this way is, if necessary, after a grain pression to the required pressure in the methanol synthesis given, where methanol is produced in the cycle process.

For reasons of process economy, efforts are made during quenching for subsequent conversion to be achieved by cooling of the gas in the quench tank just evaporates the amount of water required to carry out the CO conversion and is absorbed by the gas. In practice, a considerable excess of water is used to achieve the desired Establish saturation level in the gas. This very often shows caking. This is especially true when the amount of dust entrained in the raw gas is high.

The invention is based on the object of avoiding caking when quenching synthesis gas from fly ash reactors while minimizing the use of water for a subsequent CO conversion.

According to the invention this is achieved in that the hot raw gas "exiting the reactor" through the injection

is first cooled by water to a temperature level that is on the one hand below the slag softening and on the other hand above the thawing temperature of the raw gas. This temperature is determined by the amount of the injected water and should be 720 to 680 ⁰ C. According to the invention then the required end conditions for converting (at 210 ⁰ C saturated gas) can be set in a second quench stage.

In a further embodiment of the invention, a complete vaporization of the injected water is ytim by a droplet size of ^ 700 and reaches a gas velocity - 0.1 m / sec is in the range of the first quench.

Example;

Coal: dry raw gas: moist raw gas: H ₂ O in raw gas: reactor pressure:

6 t / h wf

10588 m ³ / h (in standard condition) 12912 m ³ / h (in standard condition) 2324 mVh = 1860 kg / h 36 bar

Reactor temperature: 14U0 ⁰ C

Water requirement for injection _:

Cooling of the raw gas of 1400 ⁰ C to 7OU ⁰ C: ³ Gas

= V _gas . Cp "_. Δ Τ = 12912 mVh 1488 KJ / m ³ K * 700 K = 13 620 507 KJ / h

Heat requirement for heating, evaporation and overheating of the injected water (100 ⁰ C):

Q ₂ = 3 3 5 OKJ / kg

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Amount of water to be dissolved: % = Q ₁ ZQ, = ⁴⁰⁶⁵ kg / h

Gas volume outlet radiation cooler:

V = 17 993 m ³ / h moist water vapor partial pressure: 15.0 bar dew point temperature: 200 ^° C.

Drop size:

For the injection ko.r.Tien pressure glands in question, with which, depending on the pre-pressure and the bore diameter, droplet sizes -? C ' ^: can be achieved, e.g.

Bore: J3 2.8 mm

Pre-pressure: 61 bar = £ p = 25 bar

Throughput per nozzle: approx. 1 100 kg / h

mean drop size: 130 μ: "

largest drop size: 290 μ

The use of several nozzles offers the advantage of higher Flexibility, since a corresponding number of Nozzles can be switched off.

An optimum is 3 to 4 nozzles, which are evenly distributed and surround the gas flow emerging from the reactor.
Evaporation time:

For the evaporation of a spherical drop of Viasser in applies to a hot gas

Nu = 2, O + 0.6 - Re ¹ ^ ² . Pr

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-G-

At low relative speeds between drops and gas (Re < _{sri) t,} that is, under unfavorable conditions, Nu = - ^ ~ - = 2 (Z)

For the gas phase around the drop, Q = of 4ΤΓ r ² (T ₁ - T ₂ ) (3)

Tj = gas temperature Ι .. = drop temperature

The gas temperature T- depends on the cooling that has already taken place, but in any case T ₁ > 70 ° C.

The evaporation of the drop takes place depending on the amount of water that has already been injected and evaporated at Ty "^ 2 (JO ⁰ C.

. From (Z) and (3) it follows for the heat transferred to the water droplets per unit of time

Q = 2 A-TT d (T ₁ -T ₂ J

λ = 0.09 W / m 'K (at T = 700 ⁰ CJ

Apply for heating and evaporation of the drop: (evaporation temperature 200 ⁰ CJ -

Q = 2375 '10 ³ J / kg

The mass of the individual drop is "Vropfen = '/ 6 · TTd' ·

This results in the evaporation times shown in FIG. 1 as a function of the droplet size. For the present Example (maximum drop diameter d = 290/1 = 1.27 x 10 "kg) results in the worst case (i.e. maximum droplet size, smallest temperature difference between gas and droplet) an evaporation time of 0.375 s.

At a gas velocity of ^ 0.1 m / sec in the first quenching area (radiation cooler), when water is injected in the area of the usual arrangement point for cleaning devices for the fin walls, it is guaranteed that the injected water evaporates completely and that no caking or deposits are present in the gas Solid particles can occur. Since cleaning devices for radiation coolers in synthesis gas plants are usually provided with pressure nozzles _; it is necessary for the first quenching according to the invention if it is also present. Devices of a synthesis gas plant only have to change their function, ie minimal effort for the structural implementation of the first quenching stage.

The second quenching stage following the first quenching stage can be of any type.

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Claims (3)

Claims 1.) Coal gasification plant with flue dust reactor working downwards against a water bath, which is followed ^by a quench for conversion "* '_ ■": Characterized in that the quenching takes place in 2 stages with water, the quenching cooling in a first stage to a temperature level that is below the slag softening on the one hand and above the thawing temperature of the raw gas on the other. 2.) Coal gasification plant according to claim 1, characterized in that the droplet size i ⁿ öer first quenching - 700 / ίπι and the gas velocity in the first quenching area is -0.1 m / sec. 3.) coal gasification plant according to claim 1 or 2, characterized in that the first quenching stage 3-4 has nozzles evenly surrounding the exiting synthesis gas stream.