EP2522857B1 - Method for the intelligent control of a compressor device with heat recovery - Google Patents

Description

Due to the general shortage of global energy resources and the climate debate about CO ₂ emissions, there is now a general trend towards efficient energy use and energy saving. Efforts are also being made in the compressor industry to be more economical with natural resources.

The following invention relates to a method for the intelligent control of a compressor unit with liquid injection, which is equipped with a heat recovery with the aim of maximizing efficiency.

From the Chinese publication CN 101 43 5420 (A ) shows a system for heat recovery and circulation on an air compressor. Here, a system is disclosed, which causes the cooling of the air compressor by means of cooling water comprising a fluid circuit of the fluid to be injected, said fluid passes through at least one heat exchanger for WRG, wherein before the compressor of the compressor system a control valve and behind the heat exchanger of the WRG a WRG-side control valve is arranged and controls an electronic control unit by means of an algorithm at least one of the two control valves and the required temperatures for the material flows of the heat recovery of the control unit can be entered as a parameter. It is the goal of this disclosure to make a control of the temperature of the cooling water and to realize a good heat recovery.

However, the control valve arranged in front of the compressor is in this case mounted directly on the radiator and thus can not be arranged as one in the compressor, by a electronic control unit regulated control valve are considered. Although the disclosed herein liquid injection compressor system is therefore equipped with a heat recovery, but it is no intelligent control with the aim of maximizing efficiency possible.

Here, the focus is on the effective cooling of the air compressor, with the invention only a better heat recovery is to be achieved, the means used for this purpose remain open. The focus remains the cooling of the air compressor. It should only be realized that the dissipated energy is also used meaningfully. Despite all this, the system continues to focus only on the requirements for ideal operation of the air compressor.

From the publication CN 2677669 is an oil-injected compressor with heat recovery described. It is hereby disclosed that the heat recovery pre-cooled the used oil after its deposition, so as to avoid negative effects of high-temperature oil with respect to the compressor and in particular to the life of the oil used. It is also disclosed that this heat removal from the heated oil a meaningful use of the waste heat of the compressor is achieved and thus a contribution to climate protection is made.

Structurally, an oil temperature control valve is provided for this purpose, which, although it can be regarded as a compressor-internal valve, is not electronically controlled in this case. In this way, however, can not realize a regulation for heat recovery in the context of the present invention, which is directed both to a cooling of the compressor, as well as the largest possible energy savings of the overall system.

Again, the orientation of the system is exhausted in its principles on the ideal operating condition of the compressor, wherein the injected oil undergoes a temperature increase depending on the load condition of the compressor, which is meaningfully removed by a heat recovery of the oil again. It should thus be achieved in this publication, both the life of the oil by a more uniform temperature as well as the compressor and at the same time make a contribution to climate protection.

However, even in this case, this does not answer the question of whether the heat recovery is optimized in any way, or whether it can run at a constant level. Rather, it is just about keeping the oil and thus the operating parameters on the heat recovery in a certain level.

The document CN 201401311Y discloses a compressor unit with heat recovery with a valve before injection into the compressor and a valve after the heat exchanger. Thus it discloses the features of the preamble of claim 1.

In the following, reference will be made to the attached schematic representation of the plant with the above reference numerals. As is known, the fluid [1] (oil or water) injected for lubrication and cooling in a compressor stage [13] is separated from the compressed air after compression of the air on the pressure side. A separator [8] separates the compressed air from the fluid, wherein the separated fluid is recycled in a circuit back to the suction side of the compressor. In the case of plants without heat recovery, the fluid is recooled to the desired temperature level for renewed injection in an internal heat exchanger [10] (water- or air-cooled).

A compressor-side control valve [6] controls the fluid injection temperature [1] to the desired fixed value. For this purpose, for example, oil temperature regulators are used in the prior art as 3/2-way valves, in which an actuated by a wax element slider controls the inflow. The oil temperature controller regulates the temperature of the oil within a fixed temperature interval, and will only ever deliver to the radiator as much oil as is required to achieve the desired oil temperature prior to injection.

In a fluid-injection-compression system according to the prior art, in this case an attempt is made to inject the fluid as cold as possible into the compressor stage [13] in order to reduce its power consumption. That is, it is primarily focused on the performance optimization of the compressor system.

However, if one considers the compressor system according to the invention with heat recovery, then the power consumption of the compressor stage [13] is no longer evaluated alone, but it is considered the entire system consisting of compressor and heat recovery. It has been found that it can make sense not to operate the compressor at the optimal performance point. To optimize the overall energy balance of the system.

In addition to the efficiency of the compressor stage, the temperature of the injected fluid also influences the temperature of the compressed air in the separating vessel [8] and at the same time the temperature of the fluid after compression [2]. In compressor systems with heat recovery this heated by the compression process fluid [2] for heating a stream [4, 5] an external heat exchanger [9] is supplied and thereby cooled itself again.

In order to prevent excessive cooling of the fluid and thus the compressor by the heat recovery, in addition to the compressor-side control valve [6], the outlet temperature of the fluid [3] from the heat exchanger [9] of the WRG with a separate WRG-side control valve ] limited to the bottom. The compressor-side and heat-recovery-side control valves [6 and 7] must be coordinated with each other to prevent the fluid temperature after the heat recovery [3] drops below the desired fluid injection temperature [1]. If the heat recovery is not required, the internal heat exchanger [10] takes over the cooling function of the compressor.

In practice, nowadays fixed regulating valves [6,7] with fixed regulating temperatures are used to regulate the fluid injection temperature [1].

In practice, there is now a situation in which the temperature of the fluid after compression [2] is either too low or too high for the heat recovery, since the requirements for a heat recovery largely depend on the requirements and the conditions of use of the user ie each user needs different inlet [4] and outlet temperatures [5] for his material stream, e.g. for a domestic water heating. These desired temperatures can then also change over time or are often known only when the compressor is installed by the user.

In speed-controlled compressors, the temperature of the fluid after compression [2] to a considerable extent (15 - 20 ° C) at lower speeds or the degree of heating of the fluid in the compression process decreases significantly, which may be the case for the desired Heat recovery systems require fluid temperatures after compression to be available only under full load conditions.

Thus, depending on the influencing parameters mentioned here, the temperature level of the fluid after compression [2], which is required for the heat recovery, will differ considerably from the required temperature depending on the load operation of the compressor during operation of the compressor system. If the fluid temperature is too low after compression and before the heat recovery, only approx. 35 - 90% of the possible energy is recovered in real operation of the compressor system.

On the other hand, a too high fluid temperature [2], which is not required for the desired temperature level of heat recovery, leads to an increased power consumption of the compressor stage of only about 2 - 5%, since the WRG does not adequately cool the fluid before entering the compression process becomes.

It is therefore the object of the present invention to provide a system in which the temperatures required for the user for the material flows [4,5] of the heat recovery of a control unit [11] can be entered as a parameter.

An algorithm stored in the control unit controls via at least one control element [6, 7] the fluid outlet temperature after the compression [2] and the fluid outlet temperature after the heat recovery [3] in the form that exactly the temperature level is reached the customer needs to recover the desired amount of heat of the plant. The increase in heat energy (10 - 65%) is significantly higher than the somewhat higher power requirement of the compressor stage (about 2 - 5%) due to an increased fluid injection temperature [1].

On the other hand, for example, the temperature level can be lowered again if temporarily no heat is removed by the heat recovery in order to reduce the performance of the compressor again.

The energy saving achievable by this intelligent control is on the order of 2 - 60%.

In another embodiment of the invention or in a supplementary second step, it is expedient to include also the regulation of the material flows of the WRG of the user with a view to a maximum efficiency in the system. In this case, as an alternative to the fluid outlet temperature after compression [2], the desired outlet temperature could be directly used as the controlled variable of the customer stream [5] are regulated. In addition, a flow control of the customer flow through a control element [12], for example, a throttle valve is conceivable that ensures a constant temperature level.

The desired temperature (5) of the medium heated by the heat recovery in the control unit (11) is used as an output parameter for the regulation of the temperature of the fluid after compression [2]. The desired temperature of the fluid after compression [2] is thus determined, for example, by the desired cooling water temperature of the user. If this cooling water is to be used e.g. reach a setpoint temperature of 95 ° C, the setpoint of the fluid temperature after compaction [2] is calculated to be 95 ° C + approx. 5 ° C = 100 ° C.

The table of FIG. 1 shows an example of a comparison of the energy recovery of a conventionally regulated heat recovery and the intelligent controlled heat recovery according to the invention.

In the case of conventionally regulated heat and power generation, 35% or 68% of the technically usable energy can be recovered in the example calculated here, with an intelligent regulation it is 100%.

In the following, an example calculation of a possible additional cost saving by an intelligently controlled heat recovery is made.

Starting point is an oil-injected screw compressor with 90kW rated power with a maximum technically recoverable heat at about 80% of the rated power of 0.8 x 90kW = 72kW.

The annual cost savings with 100% heat recovery through the intelligently controlled heat recovery according to the invention is calculated using the following parameters
4000Bh / a
0.6 Euro / liter heating oil
Heating efficiency: 75%
upper calorific value heating oil: 10.57 kWh / l) $$\frac{72\mathrm{kW}\times 40000\mathrm{Bra}/\mathrm{a}\cdot 0.6\mathrm{Euro}/\mathrm{l}}{\left(10.57\mathrm{kWh}/\mathrm{l}\cdot 0.75\right)}=21798\mathrm{Euro}/\mathrm{a}$$

The annual cost savings at 35% heat recovery through a conventionally regulated heat recovery are calculated $$0.35\times 21798\mathrm{Euro}/\mathrm{a}=7629\mathrm{Euro}/\mathrm{a}$$

The additional savings through an intelligent control WRG is therefore in this example case about 14.168 € / year.

The invention will be explained in more detail below with reference to two schematic drawings in two designs.

In the schematic representation of FIG. 2 is shown on the one hand on the left side of the compressor 13, in which a fluid is injected in the operating state 1. After compression, this fluid is separated in a separator 8 from the compression medium and transferred as fluid in the operating state 2 after compression in the second right-hand area of the system, namely in the heat recovery (WRG).

In this section, the fluid heated by the compression process enters operating mode 2 at an elevated temperature compared to operating state 1, because, depending on the load condition the compressor takes place a defined heating of the injected fluid during the compression process. This heated fluid is now supplied to a heat recovery in a heat exchanger 9, whereby it after passing through this heat recovery process in the operating state 3 cooled after heat recovery by a certain value to be defined again exits.

In the schematic representation thus results on the right side of a heat recovery area and on the left side of a compression area of the system according to the invention. Here, on the compressor side, the internal heat exchanger 10 for regulating the temperature of the fluid before injection is arranged in series with the heat exchanger 9 arranged on the heat exchanger side. Within the heat recovery is now the heat exchanger 9 downstream of a control valve 7 is provided in the illustrated embodiment, through which the cooled after the heat recovery fluid is performed.

This valve is electrically controllable according to the invention, for example, by an electric stepper motor, which takes the place of the conventional expansion element, and has two inputs A and B. Input A is in this case an input, through which the fluid can be supplied in the operating state 2, bypassing the heat recovery for regulating the temperature of the fluid in the operating state 3 after the heat recovery.

Input B is an input to the control valve 7, through which the fluid enters after the heat recovery in the cooled state. That is, via the control valve 7 is a mixture of fluids in the operating state 2, that is at elevated temperature and in the operating state 3 after the heat recovery possible so as to control the temperature to which the fluid has in the operating state 3 after heat recovery.

The heat exchanger 9 thus has a cooling medium, for example water, which is present in the operating state 4 before entering the heat exchanger 9 in the operating state 5 with increased temperature after passing through the heat exchanger 9.

In the illustrated schematic form, an additional control element 12, for example a throttle valve, is also provided in the inlet of the heat exchanger 9, by means of which the flow rate of the heat exchanger 9 with the medium to be heated can be controlled. This also serves to control the outlet temperature of the fluid in operating state 3 after heat recovery. There is a higher exit temperature in the fluid after heat recovery when reducing the flow rate of the cooling medium in the heat exchanger 9.

The fluid in the operating state 3 after the heat recovery is now fed back to the compressor side of the system, since it is guided for renewed injection into the compressor 13 in a circuit. Prior to injection into the compressor 13, another control valve 6 is part of the system, which is also electrically controlled. Depending on the desired inlet temperature 1 of the fluid during injection into the compressor 13, this control valve 6 can now either pass on the fluid in the temperature in the operating state 3 after heat recovery or carry out a regulation to reduce the temperature.

As the control valve 7, the control valve 6 for this purpose has two inputs, namely the input A, through which the fluid is supplied in the operating state 3 in a certain temperature level after heat recovery and is thus supplied to the injection.

The second input B is preceded by a cooler 10, through which the fluid can be reduced in its temperature in a defined level. By defined opening The inputs A and B can thus be set a mixing ratio of the fluid between the higher temperature in the operating state 3 and the cooled temperature after passing through the radiator 10 and so adjust the fluid in the operating state of the injection 1 exactly to a desired temperature.

It can be taken for various operating conditions of the system via the regulation of the valves 6 and 7 appropriate measures. In general operation of the heat recovery are each the possibilities to operate the valve 7 exclusively via the input B or a mixture of the inputs A and B and thus to determine the outlet temperature of the fluid 3 after heat recovery.

At the same time, both operating states of the valve 6 also apply when using the heat recovery, namely an exclusive flow through the inlet A or a connection of the inlet B and thus a defined cooling of the fluid prior to injection into the compressor 13.

If the heat recovery temporarily not operated, the fluid 2 can be performed completely by input B or in a mixing forum through input A and B or completely, bypassing the heat recovery exclusively through input A after compression, since the heat recovery does not remove temperature and thus the temperature after the heat recovery regardless of the valve position of the control valve 7 is constant. In this case, the control valve 6 can be operated in the use position of both open valves A and B or in the exclusive opening of the entrance B, as a rule, a cooling of the fluid in the event of a non-occurring heat recovery will be required in principle.

Further valve positions result from the operating states of a heat recovery, which in the use temperature raised or lowered as needed. With a desired increase in the temperature of use of the heat recovery, it is expedient to regulate the position of the inputs A and B in the valve 6 before injection to an increased flow through input A in the valve 6, since so the injection temperature of the fluid in the operating state 1 before Compressor is raised by a bypass of the radiator 10. Due to the increased injection temperature of the fluid results in a higher fluid temperature 2 after compression and thus a higher inlet temperature before heat recovery, whereby the heat recovery can be supplied to a higher temperature.

A further control component can be achieved alternatively or additionally by simultaneously throttling the cooling medium in the throttle valve 12 with a displacement towards the inlet A into the valve 6 or to an exclusive conduction of the fluid in the operating state 3 via the inlet A of the valve 6 the heat recovery 9 takes place. By reducing the flow rate through the heat recovery so the medium to be heated can be assigned a higher temperature level.

Conversely, a reduction in the temperature of use of the heat recovery would be achieved by a shift towards the input B of the valve in the control valve 6 before injection, that is, more of the fluid is passed in the operating state 3 after the recovery of heat through the radiator 10 and thus the temperature is lowered before the injection of the fluid 1. Due to the lowered injection temperature 1, there is also a reduction in the temperature 2 after separation in the separator 8 after compression before the heat recovery 9. That is, the fluid enters the heat exchanger 9 at a lower temperature, whereby here the temperature level to be cooled Medium in the output 5 can be reduced.

Again, alternatively or additionally, the use of a throttle valve 12 before entering the heat recovery is possible, in which case a lower temperature level at the output 5 can be achieved by a higher flow rate of the medium to be cooled by the heat recovery 9.

Furthermore, the system according to the invention can respond to changes in the load operation of the compressor 13 in order to maintain the desired use of heat recovery at a defined level. It is here central concern of the invention to make the heat recovery energetically optimal and thus to achieve a much better energy yield of the system of compressor and heat recovery.

When the load operation of the compressor 13 is shut down, this causes the increase of the fluid temperature in the compression process to decrease. After separation of the working medium in the separator 8 thus results in a lower fluid temperature 2 after compression. In order to make optimum use of the temperature for heat recovery, it is necessary to further open the inlet A of the control valve 6, since the fluid in the control circuit basically has a lower temperature and thus no cooling via the radiator 10 and thus the input B of the control valve 6 needs.

By bypassing the radiator 10, a higher temperature can be achieved at the inlet 1 of the fluid in the compressor 13. The heat recovery process in the heat exchanger 9 should still cause a desired heat of the medium to be heated after passing through the heat recovery in state 5. Therefore, the fluid is completely supplied to the heat recovery and not bypassed through input A of the control valve 7 around the heat recovery around. It should be possible to use the maximum heat for heat recovery.

In order to keep the medium to be heated in its operating state 5 constant in its temperature, the throttle valve 12 can also be operated in an advantageous design to reduce the flow rate of the medium to be heated by the heat exchanger 9 such that the temperature in the state 5 after heat recovery reaches the desired value.

Conversely, a startup of the load operation of the compressor 13 causes a temperature increase of the compressor fluid after compression 2 and after deposition in the separator 8. The fluid in the operating state 2 thus has a higher temperature, possibly higher than required for the heat recovery in the heat exchanger 9. It is therefore not useful, as in the previous example, to use the inlet via input A of the control valve 7, since so the heat dissipation of the fluid does not occur through the heat recovery. An increased flow of the medium to be heated via the throttle valve 12 through the heat exchanger 9 is expedient so as to adjust the temperature in the state 5 in the exit 5 from the heat exchanger 9.

A decisive control point in this operating state is the position of the control valve 6, since here by an increased diversion of the fluid in the operating state 3 via the radiator 10 and thus in the input B of the control valve 6, the input temperature of the fluid to a desired value in the operating state 1 before Compaction is adjustable. That is, by the cooling of the fluid prior to injection 1 in the compressor, a certain temperature of the fluid is adjusted after the compression in the operating state 2, which corresponds exactly to the specifications to the desired temperature of the working fluid after passing through the heat exchanger 9 in the operating state 5 to reach.

Drawing members are not shown in the drawing, which are required for the supply of the control unit with the required operating parameters. Temperature measuring elements are at least provided for the fluid temperature 2 after compression and the fluid temperature 3 after the heat recovery. Furthermore, it is expedient to measure the water temperature 5 according to the WRG, since this should comply with a desired value. If the inlet temperature 4 before the WRG is also variable, a measuring element should also be present here.

In FIG. 3 an alternative design of the system is shown, in which now the previously arranged as internally on the compressor side heat exchanger 10 is no longer connected in series with the heat exchanger 9, but has a parallel arrangement to the heat exchanger 9. This means that the fluid 2 after compression and with the temperature increased by the compression process passes through the heat exchanger 9 as described above for heat recovery, but can also pass through the second heat exchanger 10 and the control valve 7 to control the injection temperature 1 or the fluid temperature 2 be supplied through input A. In this way, it is possible to cool the fluid 3 after the heat recovery again depending on the desired operating parameters.

It is provided in this design at the control valve 6, that this is supplied to the one as before, the fluid 3 in the temperature state after the heat recovery. This time, this input B is provided in the control valve in contrast to the previous design. Input A can be controlled to control the injection temperature of the fluid 1 in the compressor with the fluid 2 with the temperature after compression directly after the separator, which can be mixed in the input A fluid a much higher temperature than the fluid 3 after heat recovery ,

From this alternative type of system, the function of the control valves 6 and 7 would change from the previous description in that now the control valve 6 takes over the task to prevent cooling of the compressor by a too low temperature of the fluid 1 at the time of injection. This would be realized by the previously described supply of fluid 2 at the temperature level after compression by the inlet A. Control valve 7 controls the fluid temperature 3 after heat recovery, whereby in turn the temperature of the fluid before the injection 1 and after the compression 2 is dependent.

Also in this system design, a control valve 12 may alternatively or additionally be provided, which regulates the flow of the medium through the heat exchanger 9. By this regulation can also the heat removal from the fluid and thus the temperature difference between the fluid after compression 2 and the fluid after heat recovery 3 are regulated. In this respect, it is also possible here to dispense with a control valve in the system in an alternative design. In this design, a waiver of control valve 6 would be possible here, if control of the fluid injection temperature would also be effected via the control valve 12.

Claims (11)

1. A compressor plant with fluid injection, comprising a fluid circuit of the fluid to be injected, wherein in the fluid circuit are arranged:

   - a compressor (13)

   - a heat exchanger (9), through which the fluid passes for purposes of heat recovery;

   - a control valve arrangement with two or three control valves (6, 7, 12) for the regulation of the injection temperature of the fluid, and the temperature of the fluid downstream of heat recovery, characterised in that, the two or three control valves are selected from the following list:

   a) a compressor-side control valve (6) for the regulation of the injection temperature of the fluid, which is arranged in the fluid circuit such that the fluid passes through the valve before it is injected into the compressor (13);

   b) a heat recovery-side control valve (7) for the regulation of the temperature of the fluid downstream of heat recovery, which is arranged in the fluid circuit such that the fluid passes through the valve after it has passed through the heat exchanger (9);

   c) a control valve (12) for the regulation of the flow of a medium through the heat exchanger (9), which is arranged in the medium inflow line into the heat exchanger (9);
   and in that,

   - an electronic control unit is provided, which regulates at least one of the control valves (6, 7, 12) by means of an algorithm, wherein the required temperatures for the heat recovery medium flows (4, 5) are entered into the control unit (11) as parameters.
2. The compressor plant in accordance with claim 1, characterised in that, the control valve arrangement additionally serves to regulate the flow of a medium through the heat exchanger (9).
3. The compressor plant in accordance with claim 1 or 2, characterised in that, the control valve arrangement comprises the compressor-side control valve (6) for the regulation of the injection temperature of the fluid, and the heat recovery-side control valve (7) for the regulation of the temperature of the fluid downstream of heat recovery.
4. The compressor plant in accordance with one of the claims 1 to 3, characterised in that, the control valve arrangement comprises the compressor-side control valve (6), the heat recovery-side control valve (7) and the control valve (12) for the regulation of the flow of the medium through the heat exchanger (9).
5. The compressor plant in accordance with one of the claims 1 to 4, characterised in that, temperature-measuring elements for the detection of at least the fluid temperature downstream of compression, and the fluid temperature downstream of heat recovery, are arranged in the fluid circuit; these supply measured data to the control unit (11).
6. The compressor plant in accordance with one of the claims 1 to 5, characterised in that, further temperature-measuring elements for the detection of the temperature of the medium downstream of heat recovery, and/or the input temperature of the medium upstream of heat recovery, are arranged in the fluid circuit; these supply measured data to the control unit (11).
7. The compressor plant in accordance with one of the claims 1 to 6, characterised in that, the desired temperature of the medium heated by heat recovery is used in the control unit (11) as the initial parameter for the regulation of the temperature of the fluid downstream of compression.
8. The compressor plant in accordance with one of the claims 3 to 7, characterised in that, on the one hand, fluid downstream of heat recovery in the heat exchanger (9) is supplied via a first inlet B to the heat recovery-side control valve (7) downstream of heat recovery, and on the other hand, fluid in the state downstream of a separator (8) is supplied via a bypass, bypassing the heat exchanger (9), and via a second inlet A to the heat recovery-side control valve (7) downstream of heat recovery, wherein alternatively a further heat exchanger (10) can be arranged in the bypass.
9. The compressor plant in accordance with one of the claims 3 to 8, characterised in that, on the one hand, fluid downstream of heat recovery in the heat exchanger (9) is supplied via a first inlet A to the compressor-side control valve (6) upstream of the injection of fluid into the compressor (13), and on the other hand, fluid is supplied via a bypass with a heat exchanger (10) to a second inlet B, for the regulation of the injection temperature.
10. The compressor plant in accordance with one of the claims 1 to 8, characterised in that, on the one hand, fluid downstream of heat recovery in the heat exchanger (9) is supplied via a first inlet B to the compressor-side control valve (6) upstream of the injection of fluid into the compressor (13), and on the other hand, fluid at the higher temperature level downstream of the separator (8) is supplied to a second inlet A, bypassing heat recovery, for the regulation of the injection temperature.
11. The compressor plant in accordance with one of the claims 3 to 10, characterised in that, slide valves with stepper motors can be used as the compressor-side and heat recovery-side control valves (6, 7); these are controlled via the electronic control unit (11).

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