Compressor for gases containing hydrogen sulfide

Details Compressor for gases containing hydrogen sulfide Compressor for gases containing hydrogen sulfide

1997-12-05

2001-01-16

Look, Edward K. (Department: 3745)

Rotary kinetic fluid motors or pumps

Including heat insulation or exchange means

Working fluid on at least one side of heat exchange wall

C416S20100A

Reexamination Certificate

active

06174131

ABSTRACT:

FIELD OF THE INVENTION
The present invention pertains to a compressor, especially a turbocompressor, for the stepwise compression of process gases containing increased percentages of hydrogen sulfide (H
2
S) with at least one impeller arranged in the H
2
S-uncritical area to the left in the direction of flow of the process gas and with at least one impeller in the H
2
S-critical area to the left and, after an external intermediate cooling, with at least one (an) impeller arranged to the right and, in an alternative embodiment, to a compressor with the same direction of flow and without external intermediate cooling.
These process gases are hydrocarbon-containing C or CH gases. These gases are also called wet gases (in English), sour gases or hydrogen sulfide gases.
These turbocompressors are used in, e.g., chemical plants or refineries, e.g., in FCC processes.
BACKGROUND OF THE INVENTION
The NACE Standard MR0175, particularly of January 1992 applies as a guideline to turbocompressors that compress gases containing hydrogen sulfide. The standard defines an operation range in which the gas being handled is at a total pressure of 65 psia (448 kPa) or greater and the partial pressure of hydrogen sulfide in the gas is greater than 0.05 psia (0.34 kPa). This guideline stipulates that the yield point of the material and consequently also the circumferential velocity of a compressor impeller must not exceed a set limit value if a combination of gas pressure and hydrogen sulfide concentration in the gas, which combination is specified in this guideline, is exceeded.
The gas composition is approximately the same in all impellers of the compressor. The pressure of the gas increases in each compressor impeller, and the final pressure is reached after the last impeller.
If the guideline is applied to any one impeller of a turbocompressor, all impellers of the compressor are designed according to this guideline in the known manner.
If the guideline is applied to all impellers of a turbocompressor, even though it does not apply, e.g., to the first impeller, all impellers of the turbocompressor have a set maximum circumferential velocity of, e.g., 260 m/sec.
Compressors of the applicant for “wet gases” and similar gases have been known with, e.g., three impellers arranged to the left in the direction of flow and three impellers arranged to the right in the direction of flow. The process gas to be compressed enters at the housing on the left, is compressed in the impellers on the left, first in the uncritical H
2
S area, and then in the critical H
2
S area, and is subjected to intermediate cooling outside the compressor. The process gas then enters the compressor on the right-hand side of the housing, is compressed on the right in the critical H
2
S area, and it leaves the compressor in the middle.
The number of impellers on the compressor shaft on the left and right is determined by the external process conditions. The circumferential velocity of all impellers is below the maximum allowable circumferential velocity, which results from the yield point of the material of the impeller, which is lowered for the H
2
S conditions.
If a defined pressure value is not exceeded according to such guideline at a defined percentage of hydrogen sulfide in the process gas, the contents of this guideline do not apply.
SUMMARY AND OBJECTS OF THE INVENTION
The primary object of the present invention is therefore not to apply, as before, this guideline to all impellers of a compressor if the conditions of the guideline are met for at least one impeller, but to apply the guideline only to the compressor impellers for which these conditions apply, rather than to the impellers to which these conditions do not apply.
According to the invention, a compressor, especially a turbocompressor, for the stepwise compression of process gases with increased percentages of hydrogen sulfide (H
2
S) is provided with at least one area that is uncritical for H
2
S with an impeller with blade end arranged to the left in the direction of flow of the process gas and with at least one H
2
S-critical area to the left as well as with an impeller with blade end arranged to the right after (downstream from) an external intermediate cooling. The impeller diameter (the circumferential velocity) of at least one impeller is increased at equal speed of rotation in the H
2
S-uncritical area. The yield point of the material of the impeller is not lowered to the H
2
S-critical limit value. At least one impeller has an impeller diameter (circumferential velocity) lower than that of the said first impeller and a material with reduced yield point is arranged in the H
2
-critical area.
According to another aspect of the invention, a compressor is provided, especially a turbocompressor, for the stepwise compression of process gases with increased percentage of hydrogen sulfide (H
2
S) with at least one impeller with blade end arranged in the H
2
S-uncritical area, and with at least one impeller with blade end and with the same direction of flow arranged in the H
2
S-critical area. The impeller diameter (the circumferential velocity) of at least one impeller is increased at equal speed of rotation in the H
2
S-uncritical area. The yield point of the material of this impeller is not reduced to the H
2
S-critical limit value. At least one impeller has an impeller diameter (circumferential velocity) smaller than that of the first impeller and a material with reduced yield point is arranged in the H
2
S-critical area.
If the guideline is not applied, e.g., to the first impeller of the turbocompressor, to which it does not apply, the circumferential velocity of this compressor impeller may be greater than that of the other impellers arranged on the compressor shaft (i.e., it may be greater than, e.g., 260 m/sec). In not applying the guideline or standard, the operation range is below a total pressure of 65 psia (448 kPa) for the gas being handled by the compressor or a partial pressure of hydrogen sulfide in the gas is less than 0.05 psia (0.34 kPa). Depending on other boundary conditions of the compression process, this can lead according to the present invention to a reduction in the size of the compressor and to a reduction in the number of compressor impellers.
According to the present invention, the gas inlet side of the first pressure stage of the compressor has or may have one compressor impeller fewer than the second pressure stage after cooling and reversal of the direction of flow instead of the same number of impellers at both stages.
Since the first impeller is not located in the critical H
2
S area, the circumferential velocity can be increased, because the yield point of the material of the first impeller of the first pressure stage does not need to be reduced to the H
2
S limit value.
The circumferential velocity is increased by increasing the impeller diameter at equal speed of rotation. The two impellers of the first pressure stage thus lead to approximately the same increase in pressure as the three impellers of the second pressure stage. The impellers of the second pressure stage in the critical H
2
S area remain unchanged.
In an alternative embodiment, a compressor is provided with the same direction of flow of the process gases to be compressed and without external intermediate cooling.
By saving one impeller, a commercial advantage is achieved over the prior-art embodiment. In addition, the first impeller of the first pressure stage, i.e., the impeller in the H
2
S-uncritical area, can be made with or without blade end, while all other impellers must be equipped with blade ends.
The state of the art and the present invention will be explained in greater detail below on the basis of schematic drawings which show exemplary embodiments.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the ac

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