Field

The present disclosure relates to a system and method for control of flue gas handling from an industrial plant into a flue gas treatment plant.

In industrial plants, such as power plants or other types of plants producing flue gases, there is often a need to process the flue gases before discharge to the environment. This may, for example, be the case if it is required or desirable to clean or remove parts from the flue gas stream. One relevant example in this respect is CO2 capture from flue gases, in order to reduce CO2 emissions.

In an embodiment, there is provided an industrial plant having a flue gas processing system. The plant comprises a flue gas stack arranged to receive flue gases from an industrial process, the stack having a discharge outlet open to the atmosphere; a suction line connected to the flue gas stack and to a flue gas processing unit; a fan operatively arranged in the suction line; a sensor; and a controller arranged to regulate the flow through the suction line based on a measured signal from the sensor.

In an embodiment, there is provided a method of controlling the operation of an industrial plant having a flue gas processing system, the method comprising the steps: operating an industrial process to produce a flue gas; flowing the flue gas to a flue gas processing unit via a suction line which is fluidly connected to a flue gas stack having a discharge outlet open to the atmosphere; operating a controller to control the flow rate of flue gas through the suction line in response to a measured signal.

The detailed description below and the appended claims outline further embodiments. Brief of the

The above objects, as well as additional objects, features and advantages of the present disclosure, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of example embodiments of the present disclosure, when taken in conjunction with the accompanying drawings.

Figure 1 shows a schematic illustration of an industrial plant having a flue gas processing system.

Figure 2 shows a schematic illustration of an industrial plant having a flue gas processing system.

Figure 3 shows a schematic illustration of an industrial plant having a flue gas processing system.

Figure 4 shows a schematic illustration of an industrial plant having a flue gas processing system.

Detailed description

Figures 1 and 2 illustrate, in a schematic manner, an industrial plant 1 having a flue gas processing system 2. The flue gas processing system 2 is configured to receive flue gases from an industrial process, here illustrated as a gas turbine 3,3a-b. The gas turbine 3,3a-b produces flue gases (exhaust) which are optionally led through a waste heat recovery heat exchanger 4,4a-b and subsequently to a flue gas stack 5,5a-b. As can be seen from Figs 1 and 2, in Fig. 1 two industrial processes are illustrated in the form of two gas turbines 3a-b, while in Fig. 2 only one gas turbine 3 is illustrated. The plant 1 may, alternatively, have more than two industrial processes, or have two or more industrial processes of different types, such as different types of power plants producing flue gas.

In Fig. 1, the two gas turbines 3a, 3b each have a dedicated flue gas stack 5a, 5b, however alternatively two or more industrial processes, such as gas turbines 3a, 3b, may be connected to a common flue gas stack 5,5a-b.

The flue gas stack 5,5a-b is arranged to receive flue gases from the industrial process(es), in this case from the gas turbine(s) 3,3a-b via the waste heat recovery heat exchanger 4,4a-b, and the stack 5,5a-b has a discharge outlet 5' (see Fig. 2) open to the atmosphere.

A suction line 6 is connected to the flue gas stack 5,5a-b and to a flue gas processing unit 8, such that the suction line 6 can transfer flue gases from the stack 5,5a-b to the processing unit 8. The suction line 6 may be in the form of a duct, however may alternatively be formed by any suitable flow channel or pipe. A fan 7 is operatively arranged in the suction line 6 for generating a flow of flue gas to the processing unit 8. The fan 7 is controllable via a regulator 11 such as to control the flow rate through the suction line 6 and/or the pressure(s) in the suction line 6. In this manner, a flue gas flow rate out of the stack 5,5a-b through the suction line 6 can be generated and/or controlled. It may, for example, often be desirable to control this flow rate so that substantially all the flue gas from the industrial process is led to the flue gas processing unit 8 for treatment. This means that the flow at the stack outlet 5' is substantially zero and that the stack is being "balanced". (This is hereafter referred to as "stack balancing control".) Alternatively, it may be an objective to maintain a supply to the processing unit 8 which matches its treatment capacity, in order to maximize utilization and/or to provide stable operating conditions for the flue gas processing unit 8.

The flue gas processing unit 8 may, for example be a CO2 removal plant.

In some applications, there may be a need for the flue gas stack 5,5a-b to remain permanently open to atmosphere, in order to prevent pressure build-up and disturbance of the industrial process. As the flue gas stack 5,5a-b, and thus also the suction line 6, then has an open connection to atmosphere via the stack 5,5a-b (specifically, via the discharge outlet 5'), the pressure levels in the stack 5,5a-b and the suction line 6 will be close to the atmospheric pressure, generally a few mbar below the atmospheric pressure to allow flow into and through the suction line 6. (1 atm = approximately 1.01325 bara).

As the pressure at the stack outlet 5' may vary with rapid variations in wind velocities around the stack 5,5a-b and the plant 1, the pressure in the stack 5,5a-b may, however, in certain applications experience dynamic variations. This can be particularly prevalent in offshore plants, where wind velocities can be higher, and/or in areas which experience more gusts and variations in wind conditions around the plant 1. If using pressure levels in the stack 5,5a-b and/or suction line 6 as a control parameter in the system, for example to control the pressure levels or flow rates, one may experience poorer control performance due to such disturbances. Referring to the embodiment illustrated in Fig. 2, a controller 11 is arranged to regulate the flow through the suction line 6 based on a signal 13 from a temperature sensor 12 and indicative of a temperature or temperature change in the suction line 6. In Fig. 2, the controller 11 is arranged to regulate an operating speed of the fan 7 based on the signal 13 indicative of a temperature or temperature change in the suction line 6. In this manner, a cooling effect and/or sudden temperature change which may follow if the stack 5,5a-b starts sucking in colder air with ambient temperature via the outlet 5' can be rapidly identified, and appropriate control action can be taken. The flue gas will normally be more than 200 deg C, hence only small amount of atmospheric air entering the flue gas flowing into the suction line 6 will create significant temperature drops which are detectable via the temperature sensor 12. In this manner, the suction rate through the suction line 6 can be adjusted so that no ambient air is drawn into the flue gas processing unit 8 via the discharge outlet 5'. This control setup therefore allows the flow rate of flue gas provided to the processing unit 8 to be adjusted according to variations in the supply rate of flue gas coming from the industrial process (here: the gas turbine 3), and thereby reduce the risk that the processing unit 8 is unintentionally supplied with flue gas which is diluted with ambient air. When such a change in temperature is detected, the flowrate from the stack 5,5a-b into the suction line 6 and further to the processing unit 8 can thus be reduced until the temperature is re-normalized by not sucking in air via the outlet 5'.

The temperature sensor 12 is in Fig. 2 illustrated as being placed near an inlet part of the suction line 6. Alternatively, the temperature sensor 12 may be placed in the stack 5,5a-b, for example, in a position in the stack 5,5a-b which is close to the suction line 6 connection, or at another position in the stack 5,5a-b which would experience a temperature change if ambient air is drawn into the stack 5,5a-b.

Fig. 3 illustrates another embodiment, having several equivalent components as those illustrated in Figs 1 and 2, which are given the same reference numerals. In Fig. 3, the controllers lla-b are operatively connected to variable flow restrictions 21a-b in the suction line 6. The flow restrictions 21a-b may, for example, be control dampers arranged in the suction line 6 and operable to vary the flow resistance and/or effective cross-sectional flow area in the suction line 6. Butterfly dampers are one type of common flow restrictions which may be suitable for this purpose.

The controller 11a can then be configured to, in response to a reduction in flue gas temperature measured by temperature sensor 12a, reduce the flow rate by adjusting the flow restriction 21a. Similarly, controller lib can be configured to regulate the flue gas flow rate via flow restriction 21b.

A suitable pressure is maintained in the suction line 6 by the fan 7, such as to allow flow of flue gases to the processing unit(s) 8. This requires there to be a negative pressure differential across the flow restriction 12a/b such that the fluid pressure downstream of the flow restriction 12a/b is lower than the pressure upsteam of the flow restriction 21a/b.

This could be achieved by setting the fan 7 to operate at a rate such that it will always create such a pressure differential when the gas turbines 3a-3b are in operation, whatever the extent to which the flow restrictions 12a/12b have been operated to restrict flow along the suction line 6. This is likely, however, to result in the fan 7 operating at much higher speeds than is actually needed to generate the required negative pressure differential for much of the time, and thus the energy being consumed by the process being much higher than it needs to be.

As such, in this embodiment, the fan 7 has its own control arrangement for this purpose, as indicated at 22, in order to maintain a desirable pressure in the suction line 6. The control arrangement 22 may, for example, be a standard feedback control loop regulating the speed of the fan 7 based on a reading from a pressure sensor 22a. The control arrangement 22 is configured to maintain the pressure at the pressure sensor 22a at a set level, which is pre-determined so that the pressure downstream of the flow restrictions 21a/21b is always lower than the pressure in the flue gas stacks 3a, 3b based on an assessment of the likely range of the pressure in the flue gas stacks 3a, 3b when the gas turbines 3a, 3b are operational. By controlling the speed of the fan 7 based on the downstream pressure measurement, the speed of the fan 7 will be reduced when the flow restrictions 21a/21b are significantly restricting the flow of gas to the suction line 6, and increased when the degree of flow restriction is decreased.

Advantageously, the pressure sensor 22a providing the control signal for the control arrangement 22 is arranged in a manifold 6' being part of the suction line 6. The flue gas flow control is then effectuated by adjusting the flow restrictions 21a-b, while the fan 7 is controlled to maintain the desired pressure in the suction line 6.

Again, this could result in the fan 7 operating at higher speeds than is actually required to generate the required negative pressure differential for much of the time, in particular when the pressure in the flue gas stacks 3a, 3b is at the higher end of the expected pressure range, and thus the energy being consumed by the process being much higher than it needs to be. When the pressure in the flue gas stacks 5a, 5b is at the higher end of the expected range, the required pressure differential across the flow strictions 21a, 21b can be generated with a higher suction line pressure than when the pressure in the flue gas stack 5a, 5b is at the lower end of the expected range. To address this, additional pressure sensors may be provided to measure the pressure upstream of each of the flow restrictions 21a, 12b. These additional pressure sensors could be provided in the flue gas stacks 5a, 5b, at the inlet part of the suction 6 with the temperature sensors 12a, 12b or directly adjacent the flow restrictions 21a, 21b. In this case, the control signals for the control arrangement 22 are provided by the pressure sensor 22a and the additional upstream pressure sensors, and the control arrangement 22 is configured to regulate the speed of the fan 7 based on the pressure differential across the flow restrictions 21a, 21b as determined from the readings from these pressure sensors, and to maintain the pressure differential at a predetermined set level.

It will be appreciated that, as in this embodiment, the suction line 6 draws flue gas from two different flue gas stacks 5a, 5b, the pressure differential across the two flow restrictions 21a, 21b may be different, depending on the pressure in each of the flue gas stacks 5a, 5b. The fan control arrangement 22 will therefore be configured to control the speed of the fan 7 such that there is a negative pressure differential across both flow restrictions 21a, 21b. For example, if both flow restrictions 21a, 21b are restricting the flow along the suction line 6 to a similar extent, this will mean that the fan 7 speed is set based on the pressure differential across whichever of the flow restrictions 21a, 21b is connected to the flue gas stack 5a, 5b at the lowest pressure.

Fig. 3 illustrates two flue gas sources (here: gas turbines 3a-b) but as will be appreciated, the plant 1 may comprise a single industrial process making up a flue gas source, or more than two industrial processes making up flue gas sources.

Fig. 4 illustrates a similar plant 1 as shown in Fig. 3, but with two flue gas processing units 8. Each flue gas processing unit 8 may have its own fan 7. The embodiment in Fig. 4 makes up an alternative implementation to that shown in Fig. 3 and otherwise functions in the same way as described above. Optionally, yet further flue gas processing units 8 may be used. Advantageously, when having more than one industrial process and/or more than one flue gas processing unit 8, each industrial process and each flue gas processing unit 8 can be fluidly connected to the manifold 6' such that the manifold 6' receives and distributes all flue gas in the system. In alternative embodiments, the temperature sensor(s) 12,12a-b described above may be a different type of sensor. Particularly, in any of the embodiments described herein the sensor(s) 12,12a-b may be (an) oxygen sensor(s) operable to measure an oxygen content of the gas stream passing by the sensor(s) 12,12a-b. A measured increase in oxygen content can be taken as an indication of influx of atmospheric air through the discharge outlet 5'. Control actions similarly as described above may be initiated based on such a sensor signal. Alternatively, in any of the embodiments described herein, the sensor(s) 12,12a-b may be combined temperature and oxygen sensor(s), whereby control action is taken by the controller 11 on the basis of both a temperature signal and an oxygen level signal. This can in some embodiments increase accuracy or otherwise improve control performance.

Alternatively, or additionally, the plant 1 may comprise a flow sensor 12' (such as one or more flowmeter(s)) arranged in the stack 5. The flow sensor 12' (see Fig. 2) produces a signal 13' indicative of a gas flow rate through (i.e. into and/or out of) the discharge outlet 5'. The signal 13' can be provided to the controller 11 and used to generate control actions similarly as described above. In any of the embodiments described herein, the plant 1 can use a flow sensor 12' and flow sensor signal 13' in conjunction with a signal from the sensor(s) 12,12a-b or independently, i.e. without the sensor(s) 12,12a-b.

In any of the embodiments described herein, the sensor may be arranged to provide a measured signal 13,13' or a calculated signal which is representative of a gas flow rate or change in gas flow rate through the discharge outlet 5'. The signal may be a direct measurement signal, a combination of measurement signals (e.g. for different operational parameters), or a calculated signal, for example calculated based on a model or look-up tables.

In any of the embodiments described herein, the controller 11 can be configured to regulate the flow through the suction line 6 such that the flow rate through the discharge outlet 5' remains at zero, close to zero, or with a positive outflow of gas from the stack 5 through the discharge outlet 5'. In this manner, an inflow of atmospheric air through the discharge outlet 5' and into the processing unit 8 can be avoided, or at least the risk thereof can be reduced. Alternatively, in some cases, it may be acceptable that some atmospheric air reaches the processing unit 8 but it is more important to avoid untreated flue gas to exit to atmosphere. In such a case, the controller 11 can be configured to regulate the flow through the suction line 6 such that the flow rate through the discharge outlet 5' remains at or close to zero, or with some inflow of gas from the stack 5 through the discharge outlet 5'. The sensor(s) used in the plant 1 may be of any suitable type for measuring temperature, oxygen and/or flow. In one embodiment, the temperature sensor may be an IR- camera operable to generate an image or heat map measuring the temperature distribution of gas at a location in the stack 5 or the suction line 6. The image or heat map may, for example, be generated on an outside surface of the stack, and thereby reflect a change in gas temperature on the inside of the stack. A control signal 13,13' can then be calculated based on the image, for example by generating a parameter for example based on the lowest temperature visible in the image or map, or based on a calculated average temperature across defined point in (or the entire) image or map. According to embodiments described herein, an open flue gas suction system is provided with improved handling of incoming flue gas from a stack, and with lower risk of pulling in ambient air, such as to provide a robust control that can handle wind gust and high wind velocities around the stack creating variation in the outside air pressure at the stack outlet.