JPH0765721B2 - Exhaust heat recovery heat exchange device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to a power generator using a gas turbine, a reciprocating engine, a fuel cell or the like as a power source, or an industrial waste such as a refuse incinerator. The present invention relates to an exhaust heat recovery heat exchange device that recovers heat from exhaust gas discharged from a material processing facility to generate steam.

(Prior Art) As a heat exchanger type of a conventional exhaust heat recovery heat exchange device, there are a water pipe boiler having a natural circulation type or forced circulation type steam-water separation drum, a forced circulation type once-through type boiler, or a full liquid type. The smoke tube type boiler of is used.

For example, as shown in FIG. 5, a conventional liquid-filled evaporator 1 is used.
Is composed of an evaporator main body 1A, a plurality of heat transfer tubes 2 arranged in the main body 1A, and an exhaust gas inlet 20 and an exhaust gas outlet 21 for sending exhaust gas to these heat transfer tubes 2. A liquid level control device 4 is attached to the body barrel 1. And
Water is supplied from a water supply inlet 25 provided at the bottom of the main body 1A to fill most of the inside of the evaporator 1 to perform heat exchange with the outer surface of the heat transfer tube 2, and take out generated steam from a steam outlet 21. It is designed to be supplied to a superheater, etc.

(Problems to be Solved by the Invention) However, among these heat exchanger types, an evaporator having a drum (body), for example, a water tube type boiler having a water / water separation drum, the above-described full-fill smoke tube In boilers, etc., the amount of water always held inside the drum is large. Therefore, it takes a long time from the start of the evaporator start up to reach a steady operating state, and until the steady state is reached, the generated steam cannot be supplied outside the heat exchange system or to the demand destination. .

On the other hand, in a once-through type boiler, since the amount of water contained therein is small, a steady state is reached in a short time after starting operation, but in order to maintain its performance, generally strict water quality control of water supply is required.

In addition, it is not a good idea to use this kind of once-through type boiler as an exhaust heat recovery boiler that does not handle high-temperature gas as much as a combustion boiler, because it has drawbacks such as a large pressure loss on the steam side.

Further, it is conceivable to use an extra-tube falling film evaporation type evaporator in which the startup time is short and the water quality control of the supply water is loose. However, the extra-pipe falling film evaporator cannot exhibit its predetermined performance unless the amount of water supplied is more than the amount of evaporation, and therefore it is necessary to constantly operate the feed water recirculation pump. Therefore, there is a drawback that power consumption is large.

The present invention has been made in view of the above problems, and shortens the time required from the start of startup to the completion of startup (steady state) as much as possible, eliminates the need for strict water quality control of water supply, and consumes less power. An object is to provide a heat recovery heat exchange device.

[Structure of Invention]

(Means for Solving the Problem) The present invention relates to an exhaust heat recovery heat exchange device that heats feed water by an evaporator that recovers heat from a gas introduced from an exhaust heat source to generate steam. The liquid level is switched between the liquid level below the lower end surface of the heat transfer tube group placed horizontally in the evaporator and the liquid level above the upper end surface of the heat transfer tube group by switching the falling film evaporator outside the tube or the full liquid type. It is characterized in that it functions as an evaporator.

(Operation) Since the present invention is configured as described above, when the liquid level of the water retained inside the evaporator is switched to the liquid level below the lower end surface of the heat transfer tube group, the exhaust heat recovery heat exchange device Functions as an extra-flowing film evaporator, and when it is switched to a liquid level above the upper end surface of the heat transfer tube group, it functions as a full liquid evaporator.

(Embodiment) An embodiment of an exhaust heat recovery heat exchanger of the present invention is shown in FIGS.
The figure will be described.

As shown in the partially broken side view of FIG. 1, in the evaporator 1 which constitutes the exhaust heat recovery heat exchange apparatus of the present invention, a large number of heat transfer tubes 2 are laterally arranged in a cylindrical evaporator main body 1A. Exhaust gas inlet 20 that receives the exhaust gas from the industrial waste treatment facility and the exhaust gas outlet that discharges the exhaust gas after exhaust heat recovery
21 are arranged at both ends of the main body 1A. Further, a pipe-shaped sprinkler 3 having a large number of sprinkler holes 3A is provided in the upper space of the main body 1A.
It is configured as a shell-and-tube type smoke tube type (extra-tube) falling film evaporator in which water is supplied from a water supply inlet 23 connected to the heat transfer tube 2 to uniformly spray the surface of the heat transfer tube 2. The steam generated by heat exchange with the outer surface of the heat transfer tube 2 is supplied from the steam outlet 24 to the superheater or the like from inside the main body 1A, and the recirculation outlet 22 is provided at the bottom of the main body 1A. Then, it is sucked by the water supply recirculation pump 14 (FIG. 3) and supplied to a predetermined location. A liquid level transmitter 4 for detecting the liquid level of the water contained inside the main body 1 is attached to the side surface of the main body 1A. Also, this evaporator 1
Then, the length and the number of the heat transfer tubes are set so that the heat transfer area is larger than the heat transfer area required to generate the steam flow rate required at the demand destination. Further, the evaporator 1 of this embodiment has a control device for controlling the liquid level of the water held therein.
30 (see second) is attached so that it can be set by switching between two normal liquid levels of the internal water of the evaporator 1 in response to a predetermined switching signal. As shown in FIG. 1, the first normal liquid level (NWL) of them is set lower than the lower end surface of the heat transfer tube group 2, and the second normal liquid level (NWL + ΔH)
Is set above the upper end surface of the heat transfer tube group 2 and is configured to function as the evaporator 1 that performs different operations by switching to any of them.

As shown in the configuration diagram of the heat exchange system in FIG. 3, the evaporator 1 is incorporated in the heat exchange system, and the superheater 6, the preheater 8 and the feed water heater 9 constitute a heat exchange device. Exhaust gas emitted from industrial waste treatment facilities, etc. passes through the switching damper 12 and the main flow path.
10 flows into the heat transfer tube 2 of the evaporator 1 through the superheater 6, and heat is exchanged between the water spray from the water spray device 3 and the outer surface of the heat transfer tube 2 to generate steam. The steam generated here is sent to the superheater 6 to be superheated, and is heated by the feed water heater 9 to be returned to the feed water tank 15 as condensed water. The exhaust gas that has undergone heat exchange in the evaporator 1 is returned to the main flow path 10 and is discharged to the outside of the system via the preheater 8. On the other hand, before entering the main flow path 10, a part of the exhaust gas flows into the bypass flow path 11 via the switching damper 13, bypasses the superheater 6 and the evaporator 1, and the exhaust gas discharged from the evaporator 1 and the main flow path. After rejoining at 10 and reaching the preheater 8, it is discharged to the outside of the system. Furthermore, the evaporator 1 has
A water supply recirculation pump 14 for sucking the internal retained water is attached, and the sucked retained water is supplied to the preheater 8 and the sprinkler device 3 of the evaporator 1. Further, the water supply and the condensate from the water supply heater 9 are once stored in the water supply tank 15, then sent to the preheater 8 via the water supply pump 16 and the water supply flow rate control valve 17 to be preheated, and then the evaporator. Water is supplied to 1.

In addition, as shown in FIG.
Is a deviation calculator 31 that receives the liquid level signal from the liquid level transmitter 4, and a PID calculator 3 that receives and amplifies the deviation calculation signal.
2. Further, an addition unit 33 for adding the feed water flow rate signal other than the liquid level signal and the steam flow rate signal, an electric / air signal conversion unit 34 for converting these electric signals into air signals and opening / closing the feed water flow rate control valve 17 It consists of and. Further, the liquid level control device 30 receives an input of a set value switching command signal such as a rated pressure reaching signal of the evaporator and evaporates into a first normal liquid level (NWL) and a second normal liquid level (NWL + ΔH). A set value switching unit 35 for switching the liquid level of the container 1 and a change rate limiting unit 36 are additionally provided. Further, a reference value of the liquid level is input to the deviation calculator 31. Further, the liquid level control device 30 monitors the fluctuation of the steam flow rate, the feed water flow rate, and the like of the heat exchange system, and the liquid level signal (single element) of the retained water inside the evaporator 1 and 3 A three-element / single-element switching section 37 for inputting a switching command signal for switching between elements (liquid level, feed water flow rate, steam flow rate), and the signal input to this switching section 37 is biased when this signal is below a threshold value. Further, a 0% bias unit 38 for applying a pressure, and a subtraction unit 39 for inputting and subtracting signals from the feed water flow rate and the steam flow rate and outputting to the switching unit 37 are additionally provided.

In the liquid level control device 30 configured in this way,
Normally, the liquid level of the water held inside the evaporator is detected by the liquid level transmitter 4, and the deviation from the set value is calculated by the deviation calculation unit 31,
When a deviation is detected, the valve operation signal is sent to the electric / air signal conversion unit 34 by skipping the addition unit 33 through the PID calculation unit 32 and adjusting the valve opening of the feed water flow rate control valve 17. Controls the liquid level of the internal retained water.

When the rated pressure of the heat exchange system reaches a specified value by the function of the falling film evaporator, for example, the minimum normal liquid level (NWL) of the evaporator to the maximum normal liquid level (NWL + Δ
In H), the set value switching command signal is received by the set value switching unit 35 to switch the set value. Then, the switching signal is corrected by the rate-of-change limiting unit 36 and then sent to the deviation calculating unit 31 to calculate the deviation from the actual liquid level, and the valve operation signal is sent to the electric / air signal converting unit 34 to supply water flow rate adjusting valve. The valve opening of 17 is adjusted to control the liquid level of the internally held water to the normal liquid level (NWL + ΔH).

Furthermore, when the liquid level control of the internal retained water is performed by using the feed water flow rate and the steam flow rate of the heat exchange system as control elements, the three-element / single-element switching unit receives the switching command signal from the single element to the three elements.
It is designed to switch between 37.

The operation of the exhaust heat recovery heat exchange device of the embodiment of the present invention thus configured will be described. First, the liquid level control device 30 attached to the evaporator 1 sets the normal liquid level of the water contained in the evaporator 1 to the minimum required height of the bottom of the evaporator 1.
Set the normal liquid level (NWL), supply water flow control valve 17 and the second
The first normal liquid level (NWL) is maintained at the set value by interlocking as shown in the figure. At this time, since the water supply recirculation pump 14 shown in FIG. 3 is operating, water circulates between the preheater 8 and the evaporator 1, and the water is sprayed from the water supply sprinkler 3 to the heat transfer tubes 2 groups. Then, heat is exchanged while flowing down the outer surface of the heat transfer tube 2, and the evaporator 1 functions as a falling film evaporator to generate steam and supply it to the superheater 6. Thus, before the start (cold start), inside the evaporator 1, there is a liquid level that functions as a falling film evaporator. Therefore, the liquid level control device 30 has the first normal liquid level.
NWL is set, and the liquid level is controlled by a single element control method in which only the liquid level signal from the liquid level transmitter 4 is used as a control element. Therefore, when the exhaust gas is supplied at a rated flow rate and temperature, the water side of the evaporator 1 reaches a predetermined pressure and temperature after a short time required for raising the temperature of the heat exchange device, the structural members of the piping, and the like. Then, steam supply is started.

By the way, the evaporator of the present invention is configured to recover a large amount of heat by further lowering the temperature from the normal exhaust gas discharge temperature (about 100 ° C to 120 ° C). Therefore, a portion of the exhaust gas is sent to the exhaust gas bypass flow passage 11 through the switching damper 13 with the vicinity of the saturated liquid state of the feed water as a boundary, and the superheater 6 and the evaporator 1 are connected.
By bypassing and bypassing the preheater 8 to the upstream side of the exhaust gas, the amount of heat exchanged in the preheater 8 is increased, and the heat exchange device is divided into the preheater 8 and the evaporator 1 without affecting the evaporation amount. , So that a large amount of water can be sent to the evaporator 1. That is, this exhaust gas bypass pipeline system
Since the heat transfer area of the evaporator 1 is too large to generate the required vapor flow rate, the exhaust gas flow rate flowing into the evaporator 1 is limited. With this, while adjusting the amount of evaporation to an appropriate amount,
High-temperature exhaust gas is directly applied to the preheater 8 to increase its heat load and preheat a feed water flow rate equal to or more than the evaporation amount to near its saturation point. As a result, it has an effect of cumulatively increasing the liquid content held in the evaporator 1.

The normal level of the liquid level control device 30 of the evaporator 1 functions as a full-fill type evaporator by the set value switching unit 35 in response to the arrival signal (setting value switching command signal) of the evaporator to reach the predetermined pressure. The second normal liquid level (NWL), which is the liquid level where the second heat transfer tube group is not exposed.
+ ΔH). Further, the liquid level control system of the liquid level control device 30 is switched by a steam flow rate signal (three elements, single element switching signal), and is a three-element control system having a feed water flow rate signal, a steam flow rate signal and a liquid level signal as elements. Has become. Under the control conditions as described above, the function described in FIG. 2 of the liquid level control device 30 gradually increases by opening the liquid level feed water flow rate adjusting valve 17 of the internal retained water in the evaporator 1, and finally reaches the full level. Rated liquid level as a liquid type evaporator (second normal liquid level,
NWL + ΔH), and the liquid level is constantly controlled by the liquid level control device 30. At the same time, the operation of the water supply recirculation pump 14 is stopped, the water spray is interrupted, heat is exchanged with the outer surface of the heat transfer tube 2, and steam is generated. Thereafter, the bypass flow rate of the exhaust gas is adjusted and sent to the evaporator 2, and excess steam is generated. The excess steam is sent to the feed water heater 9 and used for preheating the feed water.

〔The invention's effect〕

According to the exhaust heat recovery heat exchange device of the present invention, the liquid level control device provided in the evaporator can switch and control the liquid level of the water contained in the evaporator to two different normal liquid levels. for that reason,
When the evaporator is started up, it can function as an external pipe falling film evaporator, reducing the internal retained water amount to the minimum normal water level, and from the evaporator to the rated temperature, pressure and flow rate in an extremely short time. Will be able to generate steam.

In addition, after reaching the rated operation, the liquid level can be gradually increased by the control of the liquid level controller of the internal retained water to function as a full liquid evaporator. Is unnecessary, and as a result, power consumption can be saved.

[Brief description of drawings]

FIG. 1 is a partially cutaway side view of an embodiment of an evaporator constituting an exhaust heat recovery heat exchange device of the present invention, and FIG. 2 is a control block diagram of a liquid level control device for the evaporator shown in FIG. FIG. 3 is a block diagram of an embodiment of a heat exchange system to which the exhaust heat recovery heat exchange apparatus of the present invention is applied, and FIG. 4 shows another evaporator constituting the exhaust heat recovery heat exchange apparatus of the present invention. FIG. 5 is a partially cutaway side view of the embodiment, and FIG. 5 is a partially cutaway side view of a conventional liquid-filled evaporator constituting an exhaust heat recovery heat exchange device. 1 ... Evaporator, 1A ... Evaporator main body, 2 ... Heat transfer tube, 3
…… Sprinkler, 4 …… Liquid level transmitter, 20 …… Exhaust gas inlet, 21 …… Exhaust gas outlet, 22 …… Recirculating liquid outlet, 23…
… Water supply inlet, 24… Steam outlet.

Claims (3)

[Claims] 1. Exhaust heat in which feed water is heated by an evaporator that recovers heat from a gas introduced from an exhaust heat source to generate steam, and the resulting steam is heated by a superheater to generate superheated steam. In the recovery heat exchange device, the liquid level of the water retained inside the evaporator is lower than the liquid level below the lower end surface of the heat transfer tube group disposed laterally in the evaporator and above the upper end surface of the heat transfer tube group. An exhaust heat recovery heat exchanger characterized by being switched to a liquid level and functioning as a falling film evaporator or a full liquid evaporator. 2. A liquid level control device that operates as a falling film evaporator or a full-fill type evaporator is switched by a liquid level control device that operates by a set value switching command signal such as a rated pressure reaching signal of the evaporator. The exhaust heat recovery heat exchange device according to claim 1. 3. A main flow path for exhaust gas in an exhaust heat recovery heat exchange device,
A bypass passage for exhaust gas that joins the main passage upstream of the preheater by bypassing the superheater and the evaporator is provided, and a part of the exhaust gas is bypassed with the vicinity of the saturated liquid state of the feed water as a boundary. The exhaust heat recovery heat exchange device according to claim 1 or 2, wherein the exhaust heat recovery heat exchange device is sent to a path to activate the evaporator.