Method for cooling a single-component or multi-component stream

Description

SUMMARY OF THE INVENTION

The invention relates to a method for cooling a single-component or multi-component stream, in particular a hydrocarbon-rich fraction, by indirect heat exchange with the refrigerant mixture of a refrigerant mixture circuit, the refrigerant mixture being compressed at least in two stages and being separated into a lower-boiling refrigerant mixture fraction compressed to the ultimate pressure of the refrigerant mixture circuit and at least one higher-boiling refrigerant mixture fraction compressed to an intermediate pressure.

A generic method for cooling a single-component or multi-component stream is known, for example, from DE-C 19722490. Such cooling or condensing methods are used, for example, in baseload condensation plants. In this case, the lower-boiling and the higher-boiling refrigerant mixture fraction are evaporated at different temperature levels in relation to the stream to be cooled or to be condensed. By means of this procedure of separate stream routing, the temperature profile resulting in the heat exchanger or heat exchangers can be advantageously influenced. However, the procedure described in DE-C 19722490 requires a certain extra outlay in terms of apparatus and in control terms, as compared with mixture circuits in which separation of this kind does not take place.

An object of the present invention is to specify a generic method for cooling a single-component or multi-component stream, which is suitable particularly for condensing a hydrocarbon-rich stream and which requires a lower outlay in terms of apparatus and/or in control terms.

Upon further study of the specification and appended claims, other objects and advantages of the invention will become apparent.

To achieve these objects, a generic method for cooling a single-component or multi-component stream is proposed, which is characterized in that the higher-boiling refrigerant mixture fraction is pumped to the pressure of the lower-boiling refrigerant mixture fraction and is combined with the lower-boiling refrigerant mixture fraction before or immediately on commencement of indirect heat exchange.

By virtue of the higher-boiling and the lower-boiling refrigerant mixture fraction being combined, as is to be provided according to the invention, the outlay in terms of apparatus and in control terms can be reduced. In this case, however, an increase in the energy consumption of the refrigerant mixture circuit occurs. Additional investment and operating costs are caused by the pump which has to be additionally provided and by means of which the higher-boiling refrigerant mixture fraction is pumped to the pressure of the lower-boiling refrigerant mixture fraction.

Further additional refinements of the method according to the invention for cooling a single-component or multi-component stream are characterized in that

• • the pumping of the higher-boiling refrigerant mixture fraction takes place in a single-stage or multi-stage manner, and
  • the combining or intermixing of the higher-boiling and lower-boiling refrigerant mixture fractions takes place in a region of the heat exchanger which is designed especially for this purpose.

BRIEF DESCRIPTION OF THE DRAWINGS

The method according to the invention for cooling a single-component or multi-component stream and further advantageous refinements thereof will be explained in more detail in conjunction with the accompanying drawing wherein:

the FIGURE illustrates an exemplary embodiment of the invention.

The FIGURE shows a method for cooling and condensing a hydrocarbon-rich, nitrogen-containing batch fraction, in which the recovery of a highly concentrated nitrogen fraction is integrated into the condensation process. A method of this type is, for example, the subject of DE-A 102009038458, published Aug. 10, 2010, the disclosure of which is hereby incorporated by reference.

Via the line 100, a hydrocarbon-rich, nitrogen-containing batch fraction is first delivered to a drying unit A, to be provided optionally, and is then delivered via the line 101 to a heat exchanger E1. In this, the batch fraction is condensed and cooled down in relation to process streams yet to be described. The cooled-down batch fraction is fed via the line 102, in which an expansion valve d is provided, to a separating column T1. A hydrocarbon-rich, nitrogen-depleted fraction is drawn off from the sump of the latter via the line 106 and is cooled down in the heat exchanger E4. After expansion in the valve e, this fraction is delivered via the line sections 107 and 108 to a separator D1. The liquid LNG product fraction is drawn off from the sump of this separator via line 109 and is delivered to the LNG storage tank L.

A highly concentrated nitrogen fraction is drawn off from the head of the separating column T1 via the line 104; its nitrogen content usually amounts to between 90 and 100% by volume. This nitrogen fraction is heated in the heat exchangers E4 and E1 in relation to process streams to be cooled and is subsequently drawn off from the process via the line 105.

To carry out the separating process taking place in the separating column T1, a side fraction is drawn off via the line 103, cooled in the heat exchanger E4 and fed as return to the separating column T1.

A nitrogen-rich fraction is drawn off at the head of the separator D1 via the line 112. Boil-off gas, compressed by means of the compressor C2, from the LNG storage tank L is admixed to this nitrogen-rich fraction via the line 110. This stream is delivered to the heat exchanger E1 via the line 113 and is heated in relation to process streams to be cooled. The heated stream is delivered via the line 114 to a compressor unit C1 preferably of multi-stage design, is compressed in the latter to the desired condensation pressure and is subsequently admixed via the line 115 to the batch fraction 100. If necessary, or optionally, an amine scrub A′ may be provided.

The above-described process management is adopted particularly when the nitrogen concentration in the final LNG product is to be limited to 1% by volume. In the case of a higher nitrogen concentration, undesirable and hazardous stratifications could otherwise occur inside the LNG storage tank on account of different densities.

The refrigerant mixture circuit 1 to 9 configured according to the invention comprises a two-stage compressor unit C11, a separator D10 preceding this compressor unit and two separators D11 and D12 following the two compressor stages. Furthermore, in contrast to the process management described in DE-C 19722490, a pump or pump unit P11 of single-stage or multi-stage design must be provided.

The refrigerant mixture evaporated in the heat exchanger E1 in relation to the batch stream 101 to be condensed is delivered via the line 1 to the abovementioned separator D10. The gas phase drawn off from the head of this separator via the line 2 is delivered to the first compressor stage of the compressor unit C11 and is compressed by means of this to a desired intermediate pressure. The compressed refrigerant mixture, after passing through the aftercooler E11, is delivered via the line 3 to the separator D11. A higher-boiling refrigerant mixture fraction is drawn off from the sump of the latter via the line 5 and is pumped by means of the pump or pump unit P11 to the pressure of the gaseous lower-boiling refrigerant mixture fraction yet to be described. This liquid fraction is led via the line 5′, in which a regulating valve b is arranged, in front of the inlet of the heat exchanger E1.

The gas phase drawn off from the separator D11 via the line 4 is delivered to the second compressor stage of the compressor unit 11 and is compressed by means of this to the desired ultimate pressure of the refrigerant mixture circuit. The compressed refrigerant mixture, after passing through the aftercooler E12, is fed to the separator D12 via the line 6. The liquid fraction occurring in the sump of the separator is led back via the line 7, in which a regulating valve c is provided, in front of the inlet of the separator D11. The lower-boiling gaseous refrigerant mixture fraction compressed to the desired ultimate pressure is drawn off at the head of the separator D12 via the line 8 and is likewise delivered to the heat exchanger E1.

According to the invention, the liquid and the gaseous refrigerant mixture fractions 5′ and 8 are combined before or immediately on commencement of heat exchange taking place in the heat exchanger E1 and are delivered as a two-phase stream to the heat exchanger E1. The two-phase refrigerant mixture is cooled under pressure in the heat exchanger E1 and is at the same time condensed completely. At the cold end of the heat exchanger E1, the refrigerant mixture is drawn off via the line 9, is expanded in the valve a and is subsequently evaporated completely during renewed passage through the heat exchanger E1.

In contrast to the procedure described in DE-C 19722490, in the method according to the invention it is not possible to influence the temperature profile in the heat exchange E1 in a directed manner. Since this is not necessary in many applications, the method according to the invention, which results in a lower outlay in terms of apparatus and/or in control terms, can be beneficial in many applications.

The entire disclosure[s] of all applications, patents and publications, cited herein and of corresponding German Application No. DE 10 2011 010 633.2, filed Feb. 8, 2011 are incorporated by reference herein.

The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.