Field of the Invention

This invention relates to a method for operating a system of bulk material locks which are each used for filling a processing apparatus under positive pressure, which contains a process gas, such as a tank or reactor, wherein prior to filling with bulk material the locks are depressurized to atmospheric pressure and the escaping gas is collected in one or more tanks and stored for further use, and wherein prior to draining their bulk material content into the tank or reactor the locks are pressurized to its operating pressure with process gas.

Such system of bulk material locks is formed by the locks of a production plant comprising a plurality of substantially identical processing apparatuses. Prior art

Methods for operating bulk material locks, which serve for filling processing apparatuses under positive pressure, are known. A very well-known example for such method is the charging of blast furnaces in the steel industry. When depressurizing the lock, the gas is collected, dedusted and stored in a gasometer, from which it is supplied to its use, in general as fuel gas. For again pressurizing the lock, process gas is withdrawn from the blast furnace directly or after dedusting. Here, it is not required to reuse the collected gas itself for pressurizing the lock, as the blast furnace process will produce a sufficient quantity of blastfurnace gas, in order to be able to branch off the gas required for pressurizing the bulk material lock without disturbing the blast-furnace process. Cf. Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, Vol. 18, Iron, Chap. 2.5.

What is not so favorable is the situation in plants of coal gasifiers, as they are described in principle in Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, Vol. 15, Gas Production, Chap. 4.4. A typical example for this technology is described in the German laid-open publication DE 10 2007 017 402 A1 .

These coal gasifiers, also referred to as pressure gasifiers, are of the shaft-like type. In these gasifiers, solid fuels such as peat, lignite, hard coal, coke, biomass or the like are converted into a combustible product gas whose essential components are carbon monoxide and hydrogen. The shaft-like pressure gasifier is charged with the fuel from above. In the shaft, the fuel forms a fixed bed which is countercurrently traversed by a gas mixture which substantially consists of oxygen, or air, and steam. The product gas, whose temperature usually is up to 800 °C, is withdrawn in the upper region of the pressure gasifier and supplied to a purification and subsequently the utilization. The ash obtained from the fuel is discharged from the pressure gasifier at the bottom, e.g. via a rotating grate. The pressure gasification process typically is carried out at pressures between 15 and 50 bar. This results in the necessity to fill the fuel into the shaft via a bulk material lock. For handing over the bulk material, or the fuel, the lock is pressurized with product gas to the process pressure existing in the shaft of the pressure gasifier and depressurized to ambient pressure for taking up its new charge.

Other than in the blast furnaces of the steel industry, the gas represents the process product in the pressure gasification. At least in larger plants consisting of several gasifiers it therefore is worthwhile to collect the gas discharged from the locks during depressurization, to compress it again to the operating pressure of the gasification process by means of a compressor unit and feed it back into the gas product stream.

To carry out the pressurization of the locks by means of this compressor unit, however, is not possible for economic reasons, since the very large gas quantity each required at short notice would require too large and expensive compressors. For pressurizing the locks, gas must therefore be branched off from the gasification process, wherein it must be accepted that with each removal of gas for pressurizing the lock the uniform course of the gasification process is disturbed.

Therefore, it has been the object to provide a method for operating a system of bulk material locks which avoids the disadvantages of the prior art in that less depressurizing gas is obtained, which after compression must be fed back into the production process, and in that less pressurizing gas must be branched off from the production process.

Description of the Invention

The object is solved by a method with the features of claim 1 . The idea underlying the invention consists in that the locks each are depressurized in partial steps by pressure compensation with a pressure tank, so that in the one or more pressure tanks not only the gas, but also a part of the pressure energy present in the gas is stored.

The smaller the distance between the starting pressure of the lock and that of the pressure tank before pressure compensation, and the smaller the pressure tank, the more pressure energy can be stored.

How many locks can be combined to such a system consisting of several locks and the one or more pressure tanks primarily depends on the frequency and duration of the lock cycles and on the number and duration of the pressure compensation steps.

Lock cycle here is understood to be the depressurization of the lock to atmospheric pressure, filling the lock with solids, pressurizing the lock to the operating pressure of the reactor, and discharging the solids from the lock into the reactor.

The method according to the invention can be designed advantageously according to the dependent claims 2 to 5. An advantageous aspect of the invention consists in that the first depressurizing step of a lock, which is effected even before the steps to be carried out according to claim 1 , is effected by pressure compensation with another lock of the system, which already has gone through the pressurizing steps c) and d) according to claim 1 . In this way, an even larger amount of gas and pressure energy is preserved and for the lock to be pressurized less gas must be withdrawn from the gasification process, in order to achieve the necessary operating pressure in the lock for handing over the solids into the reactor.

A further preferred aspect of the invention consists in that the last step for pressurizing the lock to the operating pressure of the connected apparatus is effected in that a pressure compensation is carried out between the lock and the apparatus. In many applications, this step is problematic, since the gas withdrawn directly from the apparatus can be very hot and can contain constituents which are deposited in the lock and can lead to malfunctions. In the present case, the gas demand for this last pressurizing step is so low, however, that it can also be carried out at a high gas temperature and with a certain concentration of condensable constituents in the gas, without impairing the operability of the lock.

A further preferred aspect of the invention consists in that after carrying out the depressurizing steps a) and b) according to claim 1 a further depressurizing step takes place, in that a pressure compensation between the lock and a pressure tank, which serves as recipient tank for a compressor unit, is carried out, by means of which the gas is fed into the product stream of the plant supplied by the lock system. In this way, the process gas withdrawn from the process through the lock is recirculated and the yield of the process is increased. A further advantageous aspect of the invention consists in that after carrying out the depressurization into the recipient tank of a compression unit a further depressurization, to almost ambient pressure, is carried out by pressure compensation with a gasometer. In this way, the maximum possible amount of gas can be collected and stored. Due to the storage, the gas can be supplied to a further use, e.g. as fuel gas.

As an alternative to the storage in a gasometer, it can however also be economic to dispose of the gas via a torch. Particularly advantageously, the present invention can be used for carrying out methods for the pressure gasification of solid fuels. Since these methods are operated at pressures above the atmospheric pressure, the addition into the pressure gasifier must be effected via a lock, in order to disturb the gasification process as little as possible. While according to the prior art, the product gas necessary for the pressurization of the locks exclusively is withdrawn from the pressure gasification process, the present invention in an economic way, i.e. without the installation of large compressors, provides for carrying out the pressurization of the locks in part with the gas drained from the locks during the depressurization. In this way, less gas must be withdrawn from the pressure gasifier for pressurization and its process is disturbed less.

The invention also comprises an apparatus for operating a method according to claims 1 to 5, comprising a system of bulk material locks, at least one of which each serves for filling a processing apparatus under positive pressure, wherein the system comprises at least one pressure tank and optionally a further pressure tank with connected gas compression unit, a gasometer and a torch conduit, and wherein the locks, the tanks and the torch conduit are connected via pipe conduits such that every component can perform a gas exchange with every other component. Advantageously, the components are connected to a header conduit. In larger systems it can also be advantageous to use several header conduits, e.g. one each for the pressure tank(s), the gas compression unit, the gasometer and/or the torch conduit.

Exemplary Embodiments

Further developments, advantages and possible applications of the invention can also be taken from the following description of exemplary embodiments and the drawings. All features described and/or illustrated form the invention per se or in any combination, independent of their inclusion in the claims or their back- reference.

The drawing, Fig. 1 , by way of example shows a partial view of a system of bulk material locks according to the invention, equipped with two pressure tanks and a gasometer.

The drawing, Fig. 2, by way of example shows a partial view of a system of bulk material locks according to the invention, equipped with two pressure tanks, a gasometer and a compressor unit, of which the gas recipient tank and the compressor are shown.

In the following example, the mode of function of the method according to the invention will be described with reference to two exemplary embodiments.

Example 1

The bulk material supplied to the locks or discharged from the locks into a reactor is indicated by the flow arrows or conduits 4, 5, 6 and 7. The bulk material locks A and B as well as the pressure tanks C and D each have a volume of 12.1 m ³ . The gasometer E serves for storing the depressurizing gas at almost atmospheric pressure. The blower F serves for conveying the gas via conduit 7 to its further use, e.g. as fuel gas, or to its disposal, e.g. via a torch. The locks, pressure tanks and the gasometer are connected with each other for gas exchange via the conduits 8, 9, 10, 1 1 , 12 and the header conduit 3. The conduits 1 and 2 serve the pressure compensation of the locks with the respective tank or reactor to be filled (not shown).

Starting situation

- Lock A is filled with 54 vol-% of solids and with 46 vol-% of gas. It is at atmospheric pressure and is going be pressurized to the operating pressure of 50 bar(g) of the tank or reactor (not shown) supplied by the lock, in order to subsequently drain its solids content into the same. - Lock B has drained its solids content into the reactor (not shown) supplied by the same, is at the operating pressure of this reactor of 50 bar(g) and is going to be depressurized to atmospheric pressure, in order to again be filled with solids. - Pressure tank C is at a pressure of 29.5 bar(g).

- Pressure tank D is at a pressure of 38.8 bar(g).

- Gasometer E constantly is at nominally atmospheric working pressure. Method step 1

- Pressure compensation between lock A and pressure tank C to 20.2 bar(g).

Method step 2

- Pressure compensation between lock A and pressure tank D to 32.9 bar(g).

Method step 3

- Pressure compensation between lock A and lock B to 44.6 bar(g). Method step 4

- Pressure compensation between lock A and the reactor to 50 bar(g). Method step 5

- Pressure compensation between lock B and pressure tank D to 38.8 bar(g).

Method step 6

- Pressure compensation between lock B and pressure tank C to 29.5 bar(g). Method step 7

- Pressure compensation between lock B and the gasometer E to almost atmospheric pressure.

Due to the procedure described in this example, 40 vol-% of the gas discharged from the locks for depressurizing the same can be reused for pressurizing the locks. The remaining 60 vol-% of the depressurizing gas are discharged into the gasometer and disposed of from there via a torch and/or supplied to a use as fuel gas. In the prior art, 100 vol-% of the depressurizing gas must be treated in this way. A compression of this gas depressurized to atmospheric pressure to such an extent that it might be used for pressurizing the locks, or that it might be admixed to the product gas at the outlet of the gasification reactors, is not economically expedient.

Example 2

The bulk material supplied to the locks or discharged from the locks into a reactor is indicated by the flow arrows or conduits 4', 5', 6' and 7'. The bulk material locks A' and B' as well as the pressure tanks C and D' each have a volume of 12.1 m ³ . The gasometer E' serves for storing the depressurizing gas at almost atmospheric pressure. The blower F' serves for conveying the gas via conduit 7' to its further use, e.g. as fuel gas, or to its disposal, e.g. via a torch. The locks, pressure tanks and the gasometer are connected with each other for gas exchange via the conduits 8', 9', 10', 1 1 ', 12' and the header conduit 3'. The conduits 1 ' and 2' serve the pressure compensation of the locks with the respective tank or reactor to be filled (not shown).

In addition, the system comprises a compressor unit, represented by the gas recipient tank G whose volume is 300 m ³ and the compressor H. The gas pressure in the gas recipient tank G is kept between 3 and 4 bar(g). The compressor H compresses the gas to the product gas pressure existing at the outlet of the gasification reactors (not shown). Via conduit 13, the tank G is filled with depressurizing gas from the locks. Via conduit 14, the compressed gas is admixed to the product gas stream exiting from the gasification reactors.

Starting situation

- Lock A' is filled with 54 vol-% of solids and with 46 vol-% of gas. It is at atmospheric pressure and is going be pressurized to the operating pressure of 50 bar(g) of the tank or reactor (not shown) supplied by the lock, in order to subsequently drain its solids content into the same.

- Lock B' has drained its solids content into the reactor (not shown) supplied by the same, is at the operating pressure of this reactor of 50 bar(g) and is going to be depressurized to atmospheric pressure, in order to again be filled with solids.

- Pressure tank C is at a pressure of 29.5 bar(g).

- Pressure tank D' is at a pressure of 38.8 bar(g).

- Gasometer E' constantly is at nominally atmospheric working pressure. - Gas recipient tank G is at 3 bar(g).

Method step 1

- Pressure compensation between lock A' and pressure tank C to 20.2 bar(g).

Method step 2

- Pressure compensation between lock A' and pressure tank D' to 32.9 bar(g).

Method step 3

- Pressure compensation between lock A' and lock B' to 44.6 bar(g). Method step 4

- Pressure compensation between lock B' and the reactor to 50 bar(g). Method step 5

- Pressure compensation between lock B' and pressure tank D' to 38.8 bar(g).

Method step 6

- Pressure compensation between lock B' and pressure tank C to 29.5 bar(g).

Method step 7

- Pressure compensation between lock B' and gas recipient tank G to 4 bar(g).

Method step 8

- Pressure compensation between lock B' and the gasometer E' to almost atmospheric pressure.

Due to the procedure described in this example, 40 vol-% of the gas discharged from the locks for their depressurization can be reused for pressurizing the locks. Another 50 vol-% are compressed by means of the compression unit to such an extent that they can be admixed to the product gas stream of the gasification reactors. Only the remaining 10 vol-% must be discharged into the gasometer and be disposed of from there or be supplied to the further subordinate use, e.g. as fuel gas. List of reference numerals

A, B, A', B' bulk material lock

4, 5, 4', 5' addition of bulk material (conduits)

6, 7, 6', 7' discharge of bulk material to the reactor (conduits) 1 , 2, 7, 8, 9, 10, 1 1 , 12, 13,

1 ', 2', 7', 8', 9', 10', 1 1 ', 12', 13 pipe conduits for gas transfer

3, 3' header conduit

C, D, C, D' pressure tank

E, E' gasometer

F, F' blower

G gas recipient tank

H compressor bar(g) bar of positive pressure