METHOD FOR IDENTIFYING DAMAGE ON A COMPRESSOR

Abstract

Described herein is a method for identifying damage on a compressor having an intake side and a discharge side, including the following steps: (i) detecting measurement data of the intake pressure (p1) and intake temperature (T1) measurement variables on the intake side, as well as end pressure (p2) and end temperature (T2) on the discharge side; (ii) determining a calculated end temperature (T2b), a calculated intake temperature (T1b), a calculated end pressure (p2b) or a calculated intake pressure (p1b) as a target variable, representing a good operating state of the compressor, as a function of the measurement data of max. three of the measurement variables (p1, T1, p2, T2); (iii) determining a comparison variable from at least one of the measurement variables (p1, T1, p2, T2) not used in step (ii); and (iv) comparing the comparison variable and the target variable as a gauge of damage to the compressor.

Claims

1. A method for identifying damage on a compressor having an intake side and a discharge side, comprising the steps: (i) acquiring measurement data of the measurement variables intake pressure (p1) and intake temperature (T1) on the intake side and end pressure (p2) and end temperature (T2) on the discharge side; (ii) determining a calculated end temperature (T2b), a calculated intake temperature (T1b), a calculated end pressure (p2b) or a calculated intake pressure (p1b) as a target variable which represents a good state of the compressor, as a function of the measurement data of a maximum of three of the measurement variables (p1, T1, p2, T2); (iii) determining a comparison variable from at least one of the measurement variables (p1, T1, p2, T2) not used in step (ii); and (iv) comparing the comparison variable and the target variable as a measure of damage on the compressor; characterized in that the target variable determined in step (ii) is determined according to an isentropic compression model including the isentropic exponent (κ) of the gas to be compressed and a correction factor (η), and the correction factor (η) is adjusted on the basis of measurement data.

2. The method as claimed in claim 1, wherein in step (ii) a calculated end temperature (T2b) is determined as the target variable as a function of the measurement data of the end pressure (p2), the intake pressure (p1) and the intake temperature (T1) in accordance with the equation
T2b=T1/η.Math.(p2/p1){circumflex over ( )}(1−1/κ), and in step (iii) the measured end temperature (T2) is determined as the comparison variable, wherein the correction factor η is calculated in accordance with the equation
η=a.Math.T1+b.Math.p2/p1+c and the factors a, b and c are determined by regression from measurement data of p2, p1 and T1.

3. The method as claimed in claim 1, wherein in step (ii) a calculated intake temperature (T1b) is determined as the target variable as a function of the measurement data of the intake pressure (p1), the end pressure (p2) and the end temperature (T2) in accordance with the equation
T1b=T2.Math.η.Math.(p1/p2)−(1−1/κ), and in step (iii) the measured intake temperature (T1) is determined as the comparison variable, wherein the correction factor η is calculated in accordance with the equation
η=a.Math.T2+b.Math.p1/p2+c and the factors a, b and c are determined by regression from measurement data of end temperature (T2), intake pressure (p1) and end pressure (p2).

4. The method as claimed in claim 1, wherein in step (ii) a calculated end pressure (p2b) is determined as the target variable as a function of the measurement data of the end temperature (T2), the intake pressure (p1) and the intake temperature (T1) in accordance with the equation
p2b=p1.Math.(η.Math.T2/T1)−(κ/(κ−1)), and in step (iii) the measured end pressure (p2) is determined as the comparison variable, wherein the correction factor η is calculated in accordance with the equation
η=a.Math.p1+b.Math.T2/T1+c and the factors a, b and c are determined by regression from measurement data of intake temperature (T1), intake pressure (p1) and end temperature (T2).

5. The method as claimed in claim 1, wherein in step (ii) a calculated intake pressure (p1b) is determined as the target variable as a function of the measurement data of the intake temperature (T1), the end pressure (p2) and the end temperature (T2) in accordance with the equation
p1b=p2.Math.(T1/T2/η){circumflex over ( )}(κ/(κ−1)), and in step (iii) the measured intake pressure (p1) is determined as the comparison variable, wherein the correction factor η is calculated in accordance with the equation
η=a.Math.p2+b.Math.T1/T2+c and the factors a, b and c are determined by regression from measurement data of intake temperature (T1), end temperature (T2) and end pressure (p2).

6. The method as claimed in claim 1, wherein the compressor has a plurality of compressor stages and method steps (i) to (iv) are carried out for at least two compressor stages.

7. A computer program product with program code which, when the computer program is executed on a suitable computer system, is suitable for carrying out a method as claimed in claim 1.

8. A computer program product having a computer-readable medium and a computer program, stored on the computer-readable medium, with program code means which are suitable, when the computer program is run on a suitable computer system, for carrying out the method as claimed in claim 1.

9. The method as claimed in claim 1, wherein the compressor has a plurality of compressor stages and method steps (i) to (iv) are carried out for all the compressor stages.

Description

EXAMPLE 1

[0087] The method in accordance with the invention was applied to the third stage of a compressor in order to identify possible damage occurring there. The compressor was a six-stage, two-crank reciprocating compressor which compresses carbon monoxide from 100 mbarg at about 5° C. to 35° C. to about 325 barg. The first stage of the compressor is equipped with backflow control, with which the delivery rate of the compressor can be set between about 70% and 100% of the maximum delivery rate. The third compressor stage comprises a double-acting piston inside a cylinder. The cylinder of the third stage is so constructed that the two compression chambers on the cover side and on the crank side draw in their gas from a common intake chamber and deliver into a common discharge chamber. The machine is equipped in each compression chamber with two plate valves on each of the intake side and the discharge side. Each stage of the machine is equipped with temperature sensors and pressure sensors on the piping on the intake side and on the discharge side.

[0088] FIG. 1 shows a extract from the operating data information system of the compressor for the third compressor stage in the period from September 2015 to October 2016. The following variables are shown in the diagram, wherein the left-hand scale indicates temperatures in degrees Celsius and the right-hand scale indicates pressures in barg:

TABLE-US-00001 top curve (solid) end temperature (T2) second curve from the top (dot-dashed) calculated end temperature (T2b) middle curve (dashed) end pressure (p2) second curve from the bottom (dashed) I ntake pressure (p1) bottom curve (dotted) intake temperature (T1)

[0089] Measurement data of the measurement variables intake pressure (p1) and intake temperature (T1) on the intake side of the third stage and end pressure (p2) and end temperature (T2) on the discharge side of the third stage were continuously acquired and recorded. One measurement point per six hours was used to prepare the diagram. For better clarity, the measurement points have been faded out and joined together by interpolation.

[0090] As the target variable which represents a good state of the compressor, a calculated end temperature (T2b) of the third stage was determined as a function of the measurement data of the end pressure (p2), the intake pressure (p1) and the intake temperature (T1). The calculated end temperature (T2b) was determined according to an isentropic compression model including the isentropic exponent (κ) of the gas to be compressed and a correction factor (η). The isentropic exponent for carbon monoxide was set in the relevant pressure and temperature range at 1.4.

[0091] The calculated end temperature (T2b) was determined in accordance with the equation T2b=T1/η.Math.(p2/p1){circumflex over ( )}(1−1/κ). The correction factor (η) was determined from historical data at the value 0.972.

[0092] For the comparison with the target variable, the measured end temperature (T2) was used as the comparison variable.

[0093] In the periods from the middle of April to the middle of August 2016, the end of August 2016 and from the beginning of October 2016, the compressor was not in operation. In the period from the beginning of September to the middle of November 2015, the calculated end temperature (target variable) and the measured end temperature (comparison variable) were almost identical. This led to the conclusion that the thermodynamic machine elements were completely intact. From the end of November 2015, first differences between the measured and the calculated end temperature appeared. On the basis of experience of earlier damage, a difference of about 5° C. with a pressure ratio (p2/p1) of about 2.5 gave reason to expect slight damage to the working valves which did not yet require an immediate response.

[0094] From January 2016, the difference became greater and at the end of January reached a level of 10° C. From experience, this difference indicated valve damage with spalling at the valve plates. Once the differences had again become significantly worse from the start of February 2016, it was decided to change the valves at the next opportunity. A planned stoppage for motor maintenance at the end of March was used to check the valves. Considerable spalling was thereby found at several intake valve plates. Once the valves had been changed, no difference between the calculated and the measured end temperature was observed following start-up in the middle of August 2016.

[0095] The method in accordance with the invention, on the basis of the apparatus in accordance with the invention, thus identified damage reliably and early during operation of the compressor. Comparing the comparison variable and the target variable not only provided information on whether damage was present, but also gave a measure of the severity of the damage. On the basis thereof, it was possible to make decisions about measures for preventing a potential component failure and unplanned machine downtime.

EXAMPLE 2

[0096] The method in accordance with the invention was applied to the first stage of a compressor in order to identify possible damage occurring there. The compressor was a seven-stage, two-crank reciprocating compressor which compresses carbon monoxide from 100 mbarg at about 5° C. to 35° C. to about 325 barg. The first stage of the compressor is equipped with backflow control, with which the delivery rate of the compressor can be set between about 70% and 100% of the maximum delivery rate. The first compressor stage comprises a double-acting piston inside a cylinder. The cylinder is so constructed that the two compression chambers on the cover side and on the crank side draw in their gas from a common intake chamber and deliver into a common discharge chamber. The machine is equipped in each compression chamber with three plate valves on each of the intake side and the discharge side. Each stage of the machine is equipped with temperature sensors and pressure sensors on the piping on the intake side and on the discharge side.

[0097] FIG. 2 shows a extract from the operating data information system of the compressor for the first compressor stage in the period from December 2017 to May 2018. The following variables are shown in the diagram, wherein the left-hand scale indicates temperatures in degrees Celsius and the right-hand scale indicates pressures in barg:

TABLE-US-00002 top curve (solid) end temperature (T2) second curve from the top (dot-dashed) calculated end temperature (T2b) third curve from the top (dashed) end pressure (p2) second curve from the bottom (dotted) intake temperature (T1) bottom curve (dashed) intake pressure (p1)

[0098] Measurement data of the measurement variables intake pressure (p1) and intake temperature (T1) on the intake side of the first stage and end pressure (p2) and end temperature (T2) on the discharge side of the first stage were continuously acquired and recorded. One measurement point per six hours was used to prepare the diagram. For better clarity, the measurement points have been faded out and joined together by interpolation.

[0099] As the target variable which represents a good state of the compressor, a calculated end temperature (T2b) of the first stage was determined as a function of the measurement data of the end pressure (p2), the intake pressure (p1) and the intake temperature (T1). The calculated end temperature (T2b) was determined according to an isentropic compression model including the isentropic exponent (κ) of the gas to be compressed and a correction factor (η). The isentropic exponent for carbon monoxide was set in the relevant pressure and temperature range at 1.4.

[0100] The calculated end temperature (T2b) was determined in accordance with the equation T2b=T1/η.Math.(p2/p1){circumflex over ( )}(1−1/κ). The correction factor (η) was determined in accordance with the equation η=a.Math.T1+b.Math.p2/p1+c, wherein the factors of the correction factor were adjusted by regression from historical measurement data of p2, p1 and T1 to a=0.0004702, b=0.06183 and c=0.644289.

[0101] For the comparison with the target variable, the measured end temperature (T2) was used as the comparison variable.

[0102] In the periods from the beginning to the middle of January 2018, the end of January 2018, the beginning of February 2018, the beginning of March 2018, the end of March 2018 to the beginning of April 2018 and the beginning to the middle of May 2018, the compressor was not in operation. In the periods in which the compressor was in operation, the calculated end temperature (target variable) and the measured end temperature (comparison variable) were almost identical. This led to the conclusion that the thermodynamic machine elements were completely intact. In the period under consideration, no damage was actually found on the compressor.

[0103] In this case too, the method in accordance with the invention, on the basis of the apparatus in accordance with the invention, is capable of identifying damage reliably and early during operation of the compressor.

EXAMPLE 3 AND COMPARATIVE EXAMPLE

[0104] The method in accordance with the invention was applied to a one-stage, double-acting, two-crank reciprocating compressor which compresses hydrogen from 25 barg at about 5° C. to 35° C. to about 40 barg. Both cylinders are each equipped with an intake line and a discharge line. The compression chambers on the cover side and on the crank side obtain their gas from a common intake chamber and deliver into a common discharge chamber. The machine is equipped in each compression chamber with an annular valve on each of the intake side and the discharge side. The valves on the intake side are each equipped with hydraulic backflow control for regulating the delivery rate. The machine is equipped with temperature sensors and pressure sensors on the piping on the intake side and on the discharge side.

[0105] The machine was further equipped with a monitoring device as is known from the prior art. This monitoring device comprises temperature sensors on the valve covers of the intake side and the discharge side, which sensors detect the outside temperature of the valve covers. As soon as the measured temperature is above a limit value of 50° C., an alarm is triggered, which indicates defective valves.

[0106] FIG. 3 shows a extract from the operating data information system of the compressor in the period from September 2017 to March 2018. The following variables are shown in the diagram, wherein the left-hand scale indicates temperatures in degrees Celsius and the right-hand scale indicates the pressure ratio (p2/p1) as a dimensionless number:

TABLE-US-00003 top curve (solid) end temperature (T2) second curve from the top (solid) calculated end temperature (T2b) third curve from the top (dotted) pressure ratio (p2/p1) second curve from the bottom (dashed) valve cover temperatures 1 and 2 bottom curve (dot-dashed) intake temperature (T1)

[0107] Measurement data of the measurement variables intake pressure (p1) and intake temperature (T1) on the intake side and end pressure (p2) and end temperature (T2) on the discharge side were continuously acquired and recorded. One measurement point per six hours was used to prepare the diagram. For better clarity, the measurement points have been faded out and joined together by interpolation.

[0108] As the target variable which represents a good state of the compressor, a calculated end temperature (T2b) was determined as a function of the measurement data of the end pressure (p2), the intake pressure (p1) and the intake temperature (T1). The calculated end temperature (T2b) was determined according to an isentropic compression model including the isentropic exponent (κ) of the gas to be compressed and a correction factor (η). The isentropic exponent for hydrogen was set in the relevant pressure and temperature range at 1.4.

[0109] The calculated end temperature (T2b) was determined in accordance with the equation T2b=T1/η.Math.(p2/p1){circumflex over ( )}(1−1/κ). The correction factor (η) was adjusted on the basis of historical data to the value 0.975.

[0110] For the comparison with the target variable, the measured end temperature (T2) was used as the comparison variable.

[0111] In the periods from the middle of September to the beginning of October 2017, the end of October 2017 and the end of November 2017 to the end of January 2018, the compressor was not in operation. In October 2017, the calculated end temperature (target variable) and the measured end temperature (comparison variable) were almost identical. This led to the conclusion that the thermodynamic machine elements were completely intact. Following restarting at the end of October 2017, first differences between the measured and the calculated end temperature appeared. On the basis of experience of earlier damage, a difference of about 5° C. with a pressure ratio (p2/p1) of about 1.55 gave reason to expect damage of the working valves with minor spalling at the valve rings. The temperature sensors used for conventional monitoring on the valve covers still showed values at this time which were far below the alarm threshold of 50° C.

[0112] Following restarting at the end of January 2018, the difference became greater and in the following two months reached a level of 10° C. From experience, this difference at the low pressure ratio indicates significant valve damage with major spalling at the valve rings. Conventional monitoring did not signal any damage in this period either. The measurement values from the temperature sensors on the valve covers were even still below those in November 2017. In May 2018, the machine was taken out of operation again and the valves were checked. Valve rings with spalling were found on both valve plates.

[0113] In this case too, the method in accordance with the invention, based on the apparatus in accordance with the invention, thus detected damage reliably and early during operation of the compressor, whereas conventional monitoring by means of temperature measurement at valve covers gave no indication of possible damage.