Patent Application
20140060459
The present invention relates to a heat recovery system and a heat recovery method.
A CO2 recovery apparatus recovers carbon dioxide (CO2) which is generated when fossil fuel is burned in a thermal power plant etc. The CO2 recovery apparatus contacts water solution of amine compound (hereinafter, referred to as “absorbing liquid”) with combustion exhaust gas discharged from a boiler and eliminates CO2 included in the combustion exhaust gas to store it without discharging to ambient air.
The CO2 recovery apparatus includes an absorbing tower that contacts the combustion exhaust gas with the absorbing liquid and a regeneration tower that heats the absorbing liquid which absorbs CO2 to discharge CO2 while regenerating the absorbing liquid. The regenerated absorbing liquid is delivered to the absorbing tower and reused.
Consequently, the CO2 recovery apparatus is placed in parallel with an electric power generation plant that generates CO2, and it is desirable to establish a highly-efficient plant as a whole by integration of the CO2 recovery apparatus and the electric power generation plant.
Patent Literatures 1 and 2 disclose the technology that uses waste heat of a CO2 recovery apparatus to heat boiler supply water to be supplied to a boiler. Moreover, Patent Literature 3 discloses the technology that uses waste heat of exhaust gas discharged from a boiler to heat boiler supply water to be supplied to a boiler.
The CO2 recovery apparatus has to be heated using low-pressure steam when CO2 is discharged from the absorbing liquid which absorbs CO2. Accordingly, an output of a low-pressure steam turbine is lowered and power generation efficiency is lowered. Consequently, it is desirable to an amount of steam extracted from the low-pressure steam turbine is reduced as much as possible to suppress output lowering of the low-pressure steam turbine.
The present invention is made under such circumstances, and an object of the present invention is to provide a heat recovery system that can reduce an amount of steam extracted from a low-pressure steam turbine and a heat recovery method.
A heat recovery system according to the present invention includes: a CO2 recovery apparatus which includes an absorbing tower that absorbs CO2 in exhaust gas into absorbing liquid and a regeneration tower that discharges CO2 from the absorbing liquid that absorbed CO2 in the absorbing tower to reuse the absorbing liquid that discharged CO2 in the regeneration tower in the absorbing tower; a steam turbine; a condenser which condenses steam discharged from the steam turbine; a first heat exchange portion in which heat exchange is performed between condensed water generated in the condenser and CO2 recovered in the regeneration tower of the CO2 recovery apparatus or semi-lean solution in the CO2 recovery apparatus; a second heat exchange portion in which heat exchange is performed between the condensed water heated in the first heat exchange portion and exhaust gas discharged from a boiler; and the boiler to which the condensed water heated in the second heat exchange portion is supplied as boiler supply water.
According to this configuration, the condensed water generated in the condenser is subjected to heat exchange with CO2 recovered in the regeneration tower of the CO2 recovery apparatus or semi-lean solution in the CO2 recovery apparatus in the first heat exchange portion, and subjected to heat exchange with exhaust gas discharged from the boiler in the second heat exchange portion. Consequently, waste heat of the CO2 recovery apparatus and waste heat of a boiler exhaust system can be recovered.
In the above invention, an entire amount of condensed water generated in the condenser is used as the condensed water subjected to heat exchange in the first heat exchange portion and the second heat exchange portion.
According to this configuration, the entire amount of the condensed water generated in the condenser is subjected to heat exchange in the first heat exchange portion and the second heat exchange portion and supplied to the boiler as boiler supply water. At this time, a water supply heater that heats the condensed water and supplies it to the boiler is omitted. As a result, steam extraction from the steam turbine for the water supply heater can be eliminated, and an amount of consumption of steam is reduced, which improves turbine efficiency.
In the above invention, a water supply heater which heats the condensed water generated in the condenser by steam extracted from the steam turbine and supplies the heated condensed water to the boiler may not be included.
According to this configuration, the water supply heater that heats the condensed water and supplies it to the boiler is omitted, and the condensed water generated in the condenser is not heated by the water supply heater but subjected to heat exchange in the first heat exchange portion and the second heat exchange portion, and supplied to the boiler as boiler supply water. As a result, steam extraction from the steam turbine by the water supply heater is eliminated, and an amount of consumption of steam is reduced, which improves turbine efficiency.
In the above invention, a third heat exchange portion which heats the condensed water heated in the second heat exchange portion and returns the heated condensed water to the second heat exchange portion, and a control portion which switches between the boiler and the third heat exchange portion as a supply destination of the condensed water heated in the second heat exchange portion may be further included.
According to this configuration, by switching the supply destination, the condensed water heated in the second heat exchange portion is heated in the third heat exchange portion and again heated in the second heat exchange portion. For example, when the temperature of the condensed water supplied from the condenser is low or an amount of heat capable of heat exchange in the first heat exchange portion is small at the time of activation of the CO2 recovery apparatus, by forming a circulation route between the second heat exchange portion and the third heat exchange portion, temperature lowering of the second heat exchange portion can be prevented.
In a heat recovery method according to the present invention which uses a CO2 recovery apparatus including an absorbing tower that absorbs CO2 in exhaust gas into absorbing liquid and a regeneration tower that discharges CO2 from the absorbing liquid that absorbs CO2 in the absorbing tower and reuses the absorbing liquid that discharged CO2 in the regeneration tower in the absorbing tower, the method including: a first step of condensing steam discharged from a steam turbine; a second step of performing heat exchange between generated condensed water and CO2 recovered in the regeneration tower of the CO2 recovery apparatus or semi-lean solution in the CO2 recovery apparatus in a first heat exchange portion; a third step of performing heat exchange between the condensed water heated in the first heat exchange portion and exhaust gas discharged from a boiler in a second heat exchange portion; and a fourth step of supplying the condensed water heated in the second heat exchange portion to the boiler as boiler supply water.
In the above invention, a fifth step of heating the condensed water heated in the second heat exchange portion in a third heat exchange portion which is different from the boiler and heating the condensed water heated in the third heat exchange portion in the second heat exchange portion may be further included.
According to the present invention, when boiler supply water is heated, waste heat recovered from the CO2 recovery apparatus and waste heat recovered from the boiler exhaust system are used, so that an amount of steam extracted from the low-pressure steam turbine can be reduced.
Hereinafter, a boiler water supply system 1 according to one embodiment of the present invention will be explained with reference to
As shown in
The low-pressure steam turbine 2 is driven to rotate when medium-pressure steam is supplied from a medium pressure turbine (not shown) for example. The low-pressure steam turbine 2 is connected to a generator (not shown) via a rotation shaft, and a rotary drive force is used for power generation in the generator. The low-pressure steam turbine 2 discharges the generated low-pressure steam to the condenser 3.
The condenser 3 condenses low-pressure steam supplied from the low-pressure steam turbine 2. The generated condensed water due to condensation of low-pressure steam in the condenser 3 is supplied to the preheater 4. The temperature of the condensed water supplied from the condenser 3 to the preheater 4 is, for example, about 38° C.
To the preheater 4, the condensed water generated in the condenser 3 is supplied from the condenser 3. Moreover, to the preheater 4, CO2 recovered in a regeneration tower 27 of the CO2 recovery apparatus 11 shown in
To the gas heater 5, condensed water heated by the preheater 4 is supplied from the preheater 4. Moreover, to the gas heater 5, exhaust gas discharged from the boiler 7 is supplied. In the gas heater 5, heat exchange is performed between the condensed water heated in the preheater 4 and the exhaust gas discharged from the boiler 7. The condensed water is heated by passing through the gas heater 5, and the heated condensed water is supplied to a deaerator 6 connected to the boiler 7. By doing this, the gas heater 5 can recover waste heat of a boiler exhaust system. The temperature of the condensed water supplied from the gas heater 5 to the deaerator 6 is, for example, about 137° C.
Moreover, the condensed water generated in the condenser 3 is heated by the preheater 4 and the gas heater 5, deaerated in the deaerator 6, and introduced into the boiler 7 as boiler supply water.
As described above, according to the boiler water supply system 1 according to this embodiment, condensed water generated in the condenser 3 is subjected to heat exchange with CO2 recovered in the regeneration tower 27 of the CO2 recovery apparatus 11 or semi-lean solution in the CO2 recovery apparatus 11 in the preheater 4, and subjected to heat exchange with exhaust gas discharged from the boiler 7 in the gas heater 5. As a result, the boiler water supply system 1 can recover waste heat in the CO2 recovery apparatus 11 and waste heat in the boiler exhaust system.
Moreover, in the above-described boiler water supply system 1, the entire amount of the condensed water generated in the condenser 3 is subjected to heat exchange in the preheater 4 and the gas heater 5, not branched in a path from the condenser 3 to the boiler 7, and the condensed water is supplied to the boiler 7 as boiler supply water.
Conventionally, when condensed water generated in the condenser 3 is supplied as boiler supply water to the boiler 7, as shown in
Next, with reference to
The boiler exhaust system eliminates dust from exhaust gas discharged from the boiler 7 as well as executes desulfurization, and discharges exhaust gas to ambient air. The boiler exhaust system is constituted by, for example, an air preheater 8, the gas heater 5, a dry electric dust collector 9, a desulfurization equipment 10, a CO2 recovery apparatus 11 and a stack 12.
To the air preheater 8, ambient air is supplied from the outside. Moreover, to the air preheater 8, exhaust gas discharged from the boiler 7 is supplied. In the air preheater 8, heat exchange is performed between the ambient air to be introduced into the boiler 7 and the exhaust gas discharged from the boiler 7. The exhaust gas passing through the air preheater 8 is cooled and supplied to the gas heater 5. In addition, the ambient air passing through the air preheater 8 is heated and introduced into the boiler 7.
As described before, in the gas heater 5, heat exchange is performed between the condensed water heated by the preheater 4 and the exhaust gas discharged from the boiler 7. The exhaust gas passing through the gas heater 5 is cooled and supplied to the dry electric dust collector 9. Since the exhaust gas passes through the air preheater 8 and the gas heater 5, its temperature is lowered before it is introduced into the dry electric dust collector 9, which improves removing property of dust and SO3 in the dry electric dust collector 9.
The dry electric dust collector 9 removes dust from the cooled exhaust gas. The exhaust gas in which the dust is removed is supplied to the desulfurization equipment 10. The desulfurization equipment 10 mainly absorbs and removes sulfurous acid gas from the exhaust gas and removes dust. The exhaust gas passing through the desulfurization equipment 10 is introduced into the CO2 recovery apparatus 11.
Moreover, the CO2 recovery apparatus 11 removes CO2 from the exhaust gas. The exhaust gas in which CO2 is removed passes through the stack 12 to be discharged to ambient air. In addition, CO2 removed from the exhaust gas is compressed to be transmitted to a storage step.
As explained above, the condensed water generated in the condenser 3 is subjected to heat exchange with the exhaust gas discharged from the boiler 7 in the gas heater 5 of the boiler exhaust system. Additionally, while an arrangement is made in the order of the gas heater 5 and the dry electric dust collector 9 from the upstream side of the exhaust gas flow in the above-described boiler exhaust system, the present invention is not limited to this example, and for example, an arrangement may be made in the order of the dry electric dust collector 9 and the gas heater 5 from the upstream side of the exhaust gas flow.
Next, the CO2 recovery apparatus 11 according to this embodiment and an installation example of the preheater 4 in the CO2 recovery apparatus 11 will be explained with reference to
In the CO2 recovery apparatus 11, exhaust gas 20 including CO2 discharged from facilities such as the boiler 7 and a gas turbine (not shown) is supplied to cooling tower 22 by a not shown blower. The exhaust gas 20 supplied to the cooling tower 22 is cooled by cooling water 21 in the cooling tower 22.
The cooled exhaust gas 20 including CO2 is supplied from a lower portion of an absorbing tower 24 via an exhaust gas line 23. In the absorbing tower 24, for example, alkanolamine-based CO2 absorbing liquid 25 (amine solution) is countercurrently contacted to the exhaust gas 20. By doing this, CO2 in the exhaust gas 20 is absorbed in the CO2 absorbing liquid 25, and CO2 is removed from the exhaust gas 20 discharged from an industrial installation. Purged gas 26 in which CO2 is removed is discharged from a tower top portion 24a of the absorbing tower 24. The purged gas 26 is transmitted to ambient air from the above-described stack 12.
The CO2 absorbing liquid 25 that absorbs CO2 in the absorbing tower 24 is stored in a tower bottom portion 24b, and transmitted to the regeneration tower 27 by a pump 35.
The CO2 absorbing liquid 25 (rich solution) discharges CO2 by being heated by steam generated in a reboiler 28 in the regeneration tower 27 to be regenerated as CO2 absorbing liquid 25 (lean solution) that can absorb CO2. The regenerated CO2 absorbing liquid 25 is, after it is cooled via a heat exchanger 30 and a lean solution cooling apparatus 31 by a pump 29, supplied to the absorbing tower 24 again and reused.
The CO2 discharged from the CO2 absorbing liquid 25 in the regeneration tower 27 sequentially passes through the preheater 4, a cooler 32 and a gas-liquid separator 33, is delivered to a CO2 compression apparatus 34 to be compressed, and transmitted to the storage step.
In the regeneration tower 27 of the CO2 recovery apparatus 11, a multiple stages of (for example, two or three stages) regeneration portions are placed. Each regeneration portion includes a nozzle 36 that lowers the CO2 absorbing liquid 25 (rich solution or semi-lean solution), a packed layer 37 that countercurrently contacts the CO2 absorbing liquid which is lowered from the nozzle 36 with steam for heating and a tray portion 38 that stores the CO2 absorbing liquid 25 (semi-lean solution) in which CO2 is partially removed.
Additionally, the preheater 4 may be provided to a supply tube L1 placed on the regeneration tower 27. The supply tube L1 supplies the CO2 absorbing liquid 25 (semi-lean solution) stored in the tray portion 38 of the regeneration portion on the upper side of the preheater 4 to the packed layer 37 of the regeneration portion on the lower side of the preheater 4 via the nozzle 36. The CO2 absorbing liquid 25 (semi-lean solution) passes through the preheater 4 provided to the supply tube L1 to be cooled. At this time, in the preheater 4, heat exchange is performed between the semi-lean solution flowing in the supply tube L1 and the condensed water flowing in the boiler water supply system 1. The condensed water passing through the preheater 4 is heated.
The CO2 compression apparatus 34 includes a compressor (not shown) that compresses CO2, a cooler (not shown) that cools the compressed CO2 whose temperature is raised and a gas-liquid separator (not shown). In this embodiment, in the CO2 compression apparatus 34, the preheater 4 according to this embodiment may be placed in parallel with or instead of the cooler. At this time, in the preheater 4, heat exchange is performed between the compressed and high-temperature CO2 and the condensed water flowing in the boiler water supply system 1. The CO2 passing through the preheater 4 is cooled. On the other hand, the condensed water passing through the preheater 4 is heated.
As explained above, the condensed water generated in the condenser 3 is subjected to heat exchange with CO2 discharged from the CO2 absorbing liquid 25 in the regeneration tower 27 or CO2 compressed in the CO2 compression apparatus 34 and moreover, subjected to heat exchange with the semi-lean solution in the regeneration tower 27 of the CO2 recovery apparatus 11.
Next, a start-up method of the boiler water supply system 1 according to this embodiment will be explained.
In addition to the above configuration, as shown in
When the temperature of the condensed water supplied from the condenser 3 is low or an amount of heat capable of heat exchange in the preheater 4 is small at the time of start-up of the CO2 recovery apparatus 11, the temperature of the gas heater could be excessively lowered.
Accordingly, the temperature of the condensed water at the outlet of the preheater 4 is detected, and if the detected temperature is lower than a predetermined temperature, the degree of opening of the control valves 15 and 16 is adjusted to be throttled to supply the condensed water from the gas heater 5 to the auxiliary heater 14. Steam is supplied to the auxiliary heater 14, and heat exchange is performed between the supplied steam and the condensed water heated in the gas heater 5. By passing through the auxiliary heater 14, the condensed water is further heated, and thereafter, heated again by the gas heater 5.
Since the condensed water circulates between the gas heater 5 and the auxiliary heater 14, the temperature of the condensed water to be supplied to the gas heater 5 is raised in a short time. This prevents temperature lowering in a heat exchanger, for example, a fin tube, and corrosion due to sulfuric acid condensation on the surface of fin tube can be prevented.
After that, if the temperature of the condensed water at the outlet of the preheater 4 is higher than a predetermined temperature, the degree of opening of the control valves 15 and 16 is adjusted to be opened to reduce an amount of supply of the condensed water to the auxiliary heater 14. This moves into a normal operation, and the entire amount of the condensed water generated in the condenser 3 is, after it is subjected to heat exchange in the preheater 4 and the gas heater 5, supplied to the boiler 7 as boiler supply water.
As described above, in this embodiment, an explanation is made on the configuration that the entire amount of the condensed water generated in the condenser 3 is subjected to heat exchange in the preheater 4 and the gas heater 5 and supplied to the boiler 7 as boiler supply water. According to this configuration, as explained above, the preheater 4 and the gas heater 5 can heat the condensed water instead of the conventional low-pressure water supply heater 40 (see
Especially, in a case where a plant in which the CO2 recovery apparatus 11 and an electric power generation plant including a boiler are placed in parallel is newly installed, since a plant required for steam extraction the low-pressure steam turbine 2 for the low-pressure water supply heater 40 is unnecessary, a facility configuration of the plant can be simplified and initial cost can be reduced.
Additionally, the present invention is not limited to a case where the low-pressure water supply heater 40 is not placed. For example, as shown in
