LU103188B1 - Avoiding pressure cycling of a steam generator in standby mode - Google Patents

Abstract

The present invention relates to the device with a steam generator 10, wherein the steam generator 10 has a first side 11 and a second side 12, wherein the second side 12 is designed to generate steam, wherein the device has a first bypass line 20, wherein the first bypass line 20 is arranged to bypass the first side 11 of the steam generator 10, wherein the first bypass line 20 has a first bypass valve 22, wherein the second side 12 is connected to a steam discharge line 30, wherein the steam discharge line 30 has a steam check valve 32, wherein the second side 12 has a pressure measuring device 40, wherein the device has a control device 50, wherein the control device 50 is connected to the pressure measuring device 40 and the first bypass valve 22, wherein the control device is designed to control the first bypass valve 22 depending on the pressure detected by the pressure measuring device 40 is.

Description

thyssenkrupp Uhde GmbH 230291P00LU thyssenkrupp AG 25.08.2023 LU103188 1/9

Avoiding pressure cycling of a steam generator in standby

Operation

The invention relates to a steam generator for a plant for the production of

Ammonia, which, for example, is produced through the use of renewable energy

is subject to fluctuations and is therefore temporarily put into standby mode.

For decades, ammonia has been produced primarily using the Haber-Bosch process. In most cases, hydrogen is first produced from natural gas and then mixed with nitrogen at high pressure and high temperature in a

catalyst. Since this is an equilibrium reaction, the

Equilibrium is not shifted to the side of the products, is in a

Recirculation circuit where ammonia is separated and unreacted hydrogen and

Nitrogen is fed back into the catalyst. By using natural gas,

However, a corresponding amount of carbon dioxide is produced.

In order to produce ammonia sustainably, electrolysis of

Water is heated using renewable energy. However, this is a major difference to the previous process. If, for example, solar power is used, the day-night cycle results in a period in which no renewable energy is generated.

Energy is available, for example through the combination of solar and

Wind power can mitigate this effect somewhat, but the fundamental problem remains. Although in some regions it is theoretically possible to obtain electrical energy from the general power grid, this too is

It will be difficult to supply the country with renewable energy in the long term. Furthermore, plants are also planned that will be located in locations favorable for energy production and have no access to an electrical grid.

Water for the production of hydrogen for an ammonia synthesis plant is known, for example, from US 9 463 983 B2.

A converter for the synthesis of ammonia cannot simply be switched on and off. For example, a temperature of at least 350 °C is necessary for the reaction to take place on the catalyst. During operation, the necessary energy (to compensate for thermal losses and to heat the cooled cycle gas to the catalyst light-off temperature) is provided by the

The energy released during the reaction is generated. The remaining energy released is usually used to generate steam.

DE 10 2022 204 103 therefore discloses methods for adapting operations when the amount of renewable energy generated decreases, thus managing with a lower amount of energy. In the event of a prolonged lack of renewable energy, for example, during a prolonged period of calm, a so-called hot standby is implemented, in which all plant components are shut down, leaving only the gas circuit of the converter running, and thermal losses are compensated for by means of an electric heater.

The synthesis of ammonia is an exothermic process, so that in normal

Synthesis the resulting reaction heat must be removed from the cycle.

This is usually done with a steam generator, preferably with a

Steam superheaters are used to generate saturated steam at 261 °C and 48 bara in steam generators, for example. This can be used in a variety of ways.

Both when driving at partial load and when partially switched off, there is a

Problem. A steam generator is usually used as the first heat exchanger to remove the reaction heat from the cycle. If this is switched off via a bypass for the hot cycle gas, it cools down, which in turn leads to a

This leads to a drop in pressure in the steam generator. Therefore, the steam generator in a system powered by renewable energy must be designed to withstand high pressure cycling loads.

The object of the invention is to reduce the alternating load in the steam generator and thus simplify the design.

This object is achieved by the device with the features specified in claim 1

Features and by the method having the features specified in claim 7.

thyssenkrupp Uhde GmbH 230291P00LU thyssenkrupp AG 25.08.2023 LU103188 3/9

Advantageous further developments result from the subclaims, the following

Description and drawing.

The device according to the invention comprises a steam generator. For example, and preferably, the device serves to produce ammonia according to the Haber

Bosch process, accordingly the steam generator is preferably in

The device is preferably subject to process-related fluctuations, for example and in particular because the necessary energy is generated regeneratively, for example

Using solar or wind power. In the case of an ammonia plant, for example, the hydrogen is produced electrolytically using renewable energy. If the renewable energy is not available, for example, because it is night and/or there is no wind, the device is put into standby mode.

Steam generator has a first side and a second side. The second side for

The device is designed for steam generation, i.e., water is supplied and evaporated. The medium to be cooled, for example, the recirculation circuit after a converter for the production of ammonia, is passed through the first side. The device has a first bypass line. The first bypass line is designed to bypass the first side of the

steam generator. This allows heat loss to be minimized in standby mode, for example, to keep the amount of heat required for an electric heater to compensate for heat radiation as low as possible. The first bypass line has a first bypass valve. In normal operation, the first bypass valve is closed,

Electricity passes through the steam generator, and steam is produced regularly.

DE 10 2022 204 103, for example, discloses such a first bypass line, which is

The second side is connected to a steam discharge line. During normal operation, the steam can be used to further

parts of the system where this heat is needed, for example a

Turbine for generating electrical energy. The steam discharge line has a

Steam check valve. The steam check valve allows the steam generator to be switched on in standby

closed during operation to prevent steam and thus heat loss. The second side has a pressure measuring device. This allows the pressure inside the second side to be measured. The device has a

The control device is connected to the pressure measuring device thyssenkrupp Uhde GmbH 230291P00LU thyssenkrupp AG 25.08.2023 LU103188 4/9 and the first bypass valve. The control device is designed to control the first bypass valve depending on the pressure measured by the pressure measuring device.

pressure is formed.

This makes it possible not only to keep the first bypass valve closed during normal operation and the first control valve open during standby operation, but also to close the first bypass valve whenever the pressure in the steam generator drops, which happens due to cooling, in order to

Temperature and thus the pressure in the steam generator within a specified

The steam check valve keeps the volume constant, so that when the temperature drops, the pressure also drops. This effect is particularly strong when the steam condenses. If the pressure increases, the first bypass valve is opened, so that only the amount of heat required for the

Maintaining the pressure is necessary. This minimizes the

Energy loss or the electrical heating power to its

Compensation is possible. At the same time, however, frequent pressure changes in the

Steam generator is avoided so that it can be designed more simply.

In a further embodiment of the invention, the steam discharge line has a

Pressure relief valve. The pressure relief valve can be designed as a simple pressure relief valve. However, the pressure relief valve is preferably controllable.

Control device connected to the pressure relief valve. The control device is designed to control the pressure relief valve depending on the

If the pressure rises above an upper limit,

Pressure threshold, the control device can open the pressure relief valve and thus selectively by closing and opening the first bypass valve and by opening and

Closing the pressure relief valve specifically releases the pressure inside the second side of the

steam generator. This allows for very simple and efficient control.

In a further embodiment of the invention, the device comprises a

Steam superheater. Steam generator and steam superheater are usually connected in series, and steam is conducted in countercurrent to the medium to be heated in order to achieve the highest possible steam temperature and thus achieve high efficiency in the utilization of the thermal energy of the steam. thyssenkrupp Uhde GmbH 230291P00LU thyssenkrupp AG 25.08.2023 LU103188 5/9 The steam superheater has a third side and a fourth side. The fourth side of the steam superheater is connected to the second side of the steam generator. The steam in the second side of the

The steam generated by the steam generator is fed into the fourth side of the steam superheater and heated there further. The third side of the steam superheater is located upstream of the first side of the steam generator in terms of flow of the heating fluid. In normal operation, the heating fluid flows through the steam superheater first, thus providing the highest

temperature level to the steam and then flows already slightly cooled into the

Steam generator. The device has a second bypass line. The second

Bypass line is arranged to bypass the third side of the steam superheater. The second bypass line has a second bypass valve. The

Steam superheater is operated either in normal operation with the second bypass valve closed or in standby operation with the bypass valve open. Since the second side of the

steam generator and the fourth side of the steam superheater are connected, the pressure in the steam superheater is also adjusted by the steam generator, so that active control of the second bypass valve is not necessary. Optionally, active control of the second bypass valve can also be achieved by the

A control device may be provided to prevent, for example, condensation in the

steam superheater. Preferably, the steam check valve is located downstream of the

steam superheater, since then only one area to be controlled from the second

side and the fourth side. Of course, it would also be possible to separate these and use each one individually in the manner described above for the

To regulate the steam generator and thus keep the pressure in the steam generator and steam superheater constant separately.

In a further embodiment of the invention, the device is a system for

Production of ammonia. The steam generator and an optional and preferred

Steam superheaters are arranged in the recirculation circuit around the converter, preferably directly behind the converter in terms of flow. Particularly preferred is a plant powered by renewable energy for the production of

Ammonia, which in particular comprises an electrolysis device for producing the

hydrogen.

thyssenkrupp Uhde GmbH 230291P00LU thyssenkrupp AG 25.08.2023 LU103188 6/9

In a further embodiment of the invention, the control device is a split

Range control.

In a further aspect, the invention relates to a method for operating a device according to the invention. In particular, the method serves to operate a plant powered by regeneratively generated energy for producing ammonia according to the Haber-Bosch process. The device can be operated in regular operation or in

Standby mode. In standby mode, the steam check valve is closed and usually the first bypass valve is open. Closing the

The steam check valve ensures that no steam, and therefore no unnecessary energy, escapes from the steam generator, thus significantly reducing the required heating power. In addition to standby operation, the procedure described below for standby operation can also be used for operation with reduced throughput, as described in DE 10 2022 204 103. Here and in the following, operation with reduced throughput is also considered standby operation, since the

Steam generator is switched to standby mode, even if the converter itself is still operating at reduced throughput. The process is thus

Standby mode of the device. A target pressure window is set for the

The target pressure window is a parameter for the design of the

This is an important parameter for the steam generator, as pressure changes represent a stress. Therefore, in addition to a maximum pressure, a minimum pressure is also specified for normal operation, and the steam generator should be operated within this target pressure range.

Target pressure window has a lower pressure threshold (minimum pressure) and an upper

Pressure threshold (maximum pressure). The control device compares the

The control device closes the first pressure window when the lower pressure threshold is reached or undershot.

Bypass valve and opens when the upper

pressure threshold, the first bypass valve. This means that only the pressure in standby mode

Maintaining the pressure level really requires the energy needed and thus a simplified design of the

Steam generator without strong or frequent pressure changes.

thyssenkrupp Uhde GmbH 230291P00LU thyssenkrupp AG 25.08.2023 LU103188 7/9

A simple opening and closing with only the digital states "open" or "closed" allows for very simple control and is therefore very efficient to implement. Although such a system tends to overshoot, this can be easily compensated for by a pressure relief valve, thus reducing a pressure peak in a simple manner.

way will be avoided.

In a further embodiment of the invention, opening and closing occurs partially. This means that the first bypass valve not only has two digital positions, open and closed, but can be opened or closed further in partial steps between them. In contrast to purely digital opening and closing, this allows for more targeted control, which particularly helps prevent pressure overshoot.

In a further embodiment of the invention, the opening and closing of the first bypass valve takes place within the target pressure window depending on the detected

Pressure, so that the opening degree of the first bypass valve increases with increasing pressure and decreases with decreasing pressure. For example, the opening degree can be adjusted linearly between (lower pressure threshold) and (upper pressure threshold), so that the opening degree is ideally set so that exactly the right amount of heat is constantly supplied for a constant pressure.

In a further embodiment of the invention, the control device opens when

Reaching or exceeding the upper pressure threshold, the first

Pressure relief valve. In addition to using a simple safety pressure relief valve, active control offers better, more consistent, and more precise pressure adjustment.

This avoids the release of an unnecessarily high amount of steam, which

Energy content would then have to be provided by the electric preheater.

The device according to the invention is explained in more detail below using an embodiment shown in the drawing.

Fig. 1 exemplary device thyssenkrupp Uhde GmbH 230291P00LU thyssenkrupp AG 25.08.2023 LU103188 8/9

A first exemplary device is shown in Fig. 1. For example, the device

Component of a recirculation circuit of an ammonia plant. A heating fluid, in the case of an ammonia plant the gas stream coming from the converter, is

In control operation, the heating fluid is supplied via a heating fluid inlet 90. The first bypass valve 22 and the second bypass valve 82 are closed, so that the heating fluid is fed into the third side 71 of the steam superheater 70 and from there into the first side 11 of the steam generator 10 and is then cooled and discharged again via the heating fluid outlet 91.

On the opposite side, water is fed via the water supply 100 into the second side 12 of the

Steam generator 12, evaporated and led via the steam discharge line 30 into the fourth side 72 of the steam superheater 70 and from there further via the steam discharge line 30 to any desired consumer.

If the system is shut down, for example due to the lack of renewable energy, the first

Bypass valve 22 and the second bypass valve 82 are opened, so that the heating fluid flow is now led from the heating fluid inlet 90 via the second bypass line 80 and the first bypass line 20 to the heating fluid outlet 91. This would now, however, increase the pressure in the

Steam elevator 10 and in the steam superheater 70, and thus to a pressure change

lead to stress.

To avoid this, the steam check valve 32 is first closed. A target pressure window is defined, for example with a lower pressure threshold of 45 bara and an upper pressure threshold of 48 bara. The pressure in the second side 12 of the

steam generator 10 is detected by the pressure measuring device 40 and transmitted to the

control device 50. If the pressure falls below the lower

pressure threshold of 45 bara, the control device 50 closes the first

Bypass valve 22. This allows heating fluid to flow through the first side 11 of the

Steam generator 10, thus generating steam on the second side 12 and allowing the pressure to rise again. If the pressure rises to or above the upper pressure threshold of 48 bara, the control device 50 opens the first bypass valve 22. In addition, the control device 50 can open the pressure relief valve 60 until the pressure has fallen below the upper pressure threshold of 48 bara and then close the pressure relief valve 60 again. This way, only the heat required to heat the heating fluid is extracted. thyssenkrupp Uhde GmbH 230291P00LU thyssenkrupp AG 25.08.2023 LU103188 9/9

Pressure in the steam generator and thus also in the steam superheater 70 within the

target pressure window.

If the system is to be restarted, the steam check valve 32 is opened again and the first bypass valve 22 and the second bypass valve 82 are closed again. This allows normal operation to resume.

Reference symbol

Steam generator 1011 first side 12 second side 20 first bypass line 22 first bypass valve 30 steam discharge line 32 steam check valve 40 pressure measuring device 50 control device 60 pressure relief valve 70 steam superheater 71 third side 72 fourth side 80 second bypass line 82 second bypass valve 90 heating fluid inlet 91 heating fluid outlet 100 water inlet

Claims (11)

thyssenkrupp Uhde GmbH 230291P00LU thyssenkrupp AG 25.08.2023 LU103188 1/3 Patent claims 1. Device with a steam generator (10), wherein the steam generator (10) has a first side (11) and a second side (12), wherein the second side (12) is designed to generate steam, wherein the device has a first bypass line (20), wherein the first bypass line (20) is arranged to bypass the first side (11) of the steam generator (10), wherein the first bypass line (20) has a first bypass valve (22), wherein the second side (12) is connected to a steam discharge line (30), wherein the steam discharge line (30) has a steam check valve (32), wherein the second side (12) has a pressure measuring device (40), wherein the device has a control device (50), wherein the control device (50) is connected to the pressure measuring device (40) and the first bypass valve (22), wherein the control device is for controlling the first bypass valve (22) is designed as a function of the pressure detected by the pressure measuring device (40). 2. Device according to claim 1, characterized in that the steam discharge line (30) has a pressure relief valve (60). 3. Device according to claim 2, characterized in that the control device (50) is connected to the pressure relief valve (60), wherein the control device is designed to control the pressure relief valve (60) as a function of the pressure detected by the pressure measuring device (40). 4. Device according to one of the preceding claims, characterized in that the device comprises a steam superheater (70), wherein the steam superheater (70) has a third side (71) and a fourth side (72), wherein the fourth side (72) of the steam superheater (70) is connected to the second side (12) of the steam generator (10), wherein the third side (71) of the steam superheater (70) is arranged fluidically for the heating fluid upstream of the first side (11) of the steam generator (10), the device comprises a second bypass line (80), wherein the second bypass line (80) is arranged to bypass thyssenkrupp Uhde GmbH 230291P00LU thyssenkrupp AG 25.08.2023 LU103188 2/3 of the third side (71) of the steam superheater (70), wherein the second bypass line (80) is a second bypass valve (82). 5. Device according to claim 3 in conjunction with claim 4, characterized in that the steam check valve (32) is arranged downstream of the steam superheater (70). 6. Device according to one of the preceding claims, characterized in that the device is a plant for producing ammonia, wherein the steam generator (10) is arranged in the recirculation circuit around the converter. 7. Device according to one of the preceding claims, characterized in that the control device is a split-range controller. 8. A method for operating a device according to one of the preceding claims, wherein the method is carried out during a standby operation of the device, wherein a target pressure window is defined for the steam generator (10), wherein the target pressure window has a lower pressure threshold and an upper pressure threshold, wherein the control device compares the pressure detected by the pressure measuring device (40) with the target pressure window, wherein the control device closes the first bypass valve (22) when the lower pressure threshold is reached or undershot, wherein the control device opens the first bypass valve (22) when the upper pressure threshold is reached or overshot. 9. Method according to claim 8, characterized in that the opening and closing takes place partially. 10. Method according to one of claims 8 to 9, characterized in that the opening and closing of the first bypass valve (22) within the target pressure window takes place as a function of the detected pressure, so that the degree of opening of the first bypass valve (22) increases with increasing pressure and decreases with decreasing pressure. thyssenkrupp Uhde GmbH 230291P00LU thyssenkrupp AG 25.08.2023 LU103188 3/3 11. Method according to one of claims 8 to 10, characterized in that the control device opens the first pressure relief valve (60) when the upper pressure threshold is reached or exceeded.