JPS6047481B2 - Internal combustion engine exhaust gas heat recovery method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for recovering heat from exhaust gas of an internal combustion engine.

2. Description of the Related Art Conventionally, as a device for recovering exhaust gas heat from a diesel engine in a ship or the like, a device that generates steam using an exhaust gas economizer as shown in FIG. 1 has been known.

The device system in FIG. 1 includes an exhaust gas economizer 1 that includes piping systems for a preheating section 11, a steam section 12, and a superheating section 13, and heats water supplied to the preheating section 11 and the steam section 12 of the exhaust gas economizer. a main steam separation drum 2 for separating steam from the anhydrous mixed fluid exiting the steam section 12, and a turbine 21 to which superheated steam from the superheating section 13 is supplied (this is a generator 22 It is mainly composed of (connected to). In the above configuration, the exhaust gas generated from the diesel engine is
As shown in , it is introduced into the economizer 1 to generate steam and recover its heat amount.

Water is supplied to the exhaust gas economizer 1 by the main water supply pump 7, heated by the surface type feed water heater 4, and then discharged to the main steam separation drum 2 which also serves as the steam drum of the auxiliary boiler. Collected water led from the evaporation section 12; mixed with mixed fluid and returned to the surface type feed water heater 4 by the feed water circulation pump 3 as boiler circulating water;
Furthermore, the preheating section 11 of the exhaust gas economizer is connected to the pipe 4A.
will be introduced in Furthermore, the steam section 12 of the exhaust gas economizer
After generating steam, it is discharged to the main steam separation drum 2 as a collected mixed fluid. The saturated steam separated in the main steam separation drum 2 is partially used as miscellaneous steam for heating fuel oil, etc., and its drain is led to the drain tank 26, but the other main steam is used in the superheating section 1 of the exhaust gas economizer.
3, which drives the turbo generator steam turbine 21 as superheated steam, and after condensing the exhaust gas in the condenser 23, it is discharged to the drain tank 26 by the condensation pump 24, and further by the main water supply pump 7. It is sucked and returned to the feed water heater 4.
The solid line in FIG. 2 shows temperature changes on the exhaust gas side and the circulating water supply side in the exhaust gas economizer 1 of the conventional device.

In the figure, T is the exhaust gas inlet temperature of the exhaust gas economizer, TO is the exhaust gas outlet temperature, T1 is the exhaust gas temperature between the preheating section 11 and the evaporation section 12 of the exhaust gas economizer, and T2 is the temperature between the evaporation section 12 and superheating. T is the temperature of the exhaust gas during the heating section 13, T is the circulating feed water inlet temperature of the preheating section 11, Ts is the saturation temperature of the circulating feed water of the steam section 12, and TO is the temperature of the circulating feed water of the steam section 12.
3, the superheated steam outlet temperature ΔTO is the circulating water supply inlet temperature Ti and the exhaust gas outlet temperature T of the preheating section 11. The terminal temperature difference Δt1 is the terminal temperature difference between the circulating water supply outlet temperature Ts of the steam section 12 and the exhaust gas inlet temperature L. By the way, in order to increase the exhaust gas heat recovery rate of a diesel engine, the exhaust gas outlet temperature T of the exhaust gas economizer must be adjusted.

It is preferable to lower it as much as possible. Furthermore, the circulating water supply temperature T at the inlet of the preheating section of the exhaust gas economizer, and the exhaust gas outlet temperature T. to increase the surface temperature of the exhaust gas economizer tube by maintaining the temperature above a certain temperature to prevent sulfuric acid corrosion caused by sulfuric acid contained in the exhaust gas, and to increase the saturation temperature Ts of the steam mixture steam in the steam section 12 of the exhaust gas economizer. In order to make the terminal temperature difference Δt1 between and the exhaust gas temperature T1 appropriate for the dimensions of the exhaust gas economizer,
It is usually important to keep the temperature at 15 to 20°C. but,
In the conventional device described above, the circulating water supply temperature T at the inlet of the preheating section of the exhaust gas economizer is kept at a constant temperature (usually 130°C ~
140℃), the steam section 1 of the exhaust gas economizer
2 terminal temperature difference Δ is a constant value (15 to 2
0℃), the exhaust gas outlet temperature T at the exhaust gas economizer outlet. Therefore, the heat recovery rate of the exhaust gas cannot be increased, and the exhaust gas outlet temperature T. If the exhaust gas heat recovery rate is increased by lowering T to an allowable value, there is a drawback that the feed water temperature T at the inlet of the preheating section of the exhaust gas economizer must fall to a range where sulfuric acid corrosion may occur. An object of the present invention is to provide a method and apparatus for recovering exhaust gas heat from an internal combustion engine, which can eliminate the drawbacks of the prior art described above and increase the heat recovery rate as much as possible while preventing sulfuric acid corrosion of heat exchanger tubes of an exhaust gas economizer. be. In order to achieve the above object, the method of the present invention sequentially supplies water heated by a feed water heater to each piping system of a preheating section, a steam section, and a superheating section of an exhaust gas economizer, and extracts superheated steam from the superheating section. In an exhaust gas heat recovery method for an internal combustion engine, the flow rate of circulating water to the feed water heater is adjusted so that the temperature difference between the exhaust gas and feed water at the inlet of the steam section and the temperature difference between the exhaust gas and feed water at the inlet of the preheating section are almost the same. and regulating temperature.

Further, an apparatus for carrying out the method of the present invention includes an exhaust gas economizer having piping systems for a preheating section, a steam section, and a superheating section;
a water heater for supplying water to the piping system of the exhaust gas economizer; a main steam separation drum for separating steam from the steam/water mixture exiting the exhaust gas economizer; and at least a portion of the steam separated by the main steam separation drum. A piping system that supplies the superheating part of the exhaust gas economizer and further sends it to the steam turbine, a piping system that condenses the steam from the steam turbine in a condenser and then circulates it to the feed water heater; In an exhaust gas heat recovery device for an internal combustion engine, which is equipped with a piping system that supplies the condensed water separated by the steam separation drum to the feedwater heater, the piping system that returns the condensed water separated by the main steam separation drum to the feedwater heater. , characterized in that the condensed water flow rate regulating means and heat exchange means are provided.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 3 is an apparatus system diagram showing an embodiment of the present invention.

The difference from the conventional device shown in FIG. 1 is that a mixing type feed water heater 6 is used instead of the surface type feed water heater 4, and the main steam separation drum
A low-pressure steam generator 5 is provided in the circulating water piping system from the main steam separation drum 2 to the feed water heater 6, and the steam generator 5 and pump 3 preheat the exhaust gas economizer 1. By changing the flow rate or temperature of the feed water supplied to the
This makes it possible to adjust the temperature to 0°C. In other words, the terminal temperature difference (T1 - Ts = Δt1) between the exhaust gas inlet side and the water supply outlet side of the exhaust gas economizer l preheating section 11 is a major factor determining the area of the exhaust gas economizer 1, and if the terminal temperature difference at the pinch point is kept small, ,
Although the amount of recovered heat increases, the heat transfer area increases exponentially, so the lower limit of the terminal temperature difference is usually set at about 15°C. Therefore, in the present invention, in order to increase the amount of recovered heat while maintaining this temperature difference, in FIG. 2, the temperature gradient (Ti→TO) on the exhaust gas side and the concentration gradient (Ti- Ts) to be as equal as possible, specifically, as shown by the dotted line in FIG. 2, the terminal temperature differences Δt1 and ΔTO of the exhaust gas and circulating supply water at the entrance and exit of the preheating section of the exhaust gas economizer are approximately equal. This makes it possible to set the amount of water circulating in the preheating section of the exhaust gas economizer. In FIG. 3, the water supply Q, which is supplied by the main water supply pump 7,
The circulating water Q, sucked from the main steam separation drum (or boiler steam drum) 2 by the feed water circulation pump 3 is sent to the low pressure steam generator 5, where it generates low pressure steam q1, and then is mixed. The mixed heat is exchanged by the type feed water heater 6,
Passes through the preheating section 11 and evaporation section 12 of the exhaust gas economizer,
After exchanging heat with the exhaust gas Qg of the internal combustion engine and generating steam, it is introduced into the main steam separation drum 2 as a steam/water mixed fluid.

A part of the saturated steam separated by the main steam separation drum 2 is used as miscellaneous steam Q, which requires relatively high pressure steam. The drain is led to the miscellaneous equipment 25 such as an engine fuel oil heater, and the drain is returned to the drain tank 26, but the other saturated steam is superheated in the superheating part 13 of the exhaust gas economizer and is sent to the steam turbine 21 for the generator. After being driven, the water is condensed in a condenser 23 and then introduced into a drain tank 26 by a condensate pump 24. Low-pressure steam q1 generated by the low-pressure steam generator 5 is supplied to fuel tank heating and other miscellaneous equipment 52, and its condensate is sent to the low-pressure steam generator 5 by a low-pressure water supply pump 51.

Note that, without providing the low-pressure steam generator 5, as shown in FIG. 4, the circulating water is directly guided from the feed water circulation pump 3 to the miscellaneous equipment 52A, and after being used for hot water heating, it is returned to the mixed feed water heater 6. is also possible. According to the above embodiment, the temperature gradient (T, -Ts) on the circulating water supply side in the preheating section 11 of the exhaust gas economizer is changed from the temperature gradient (T1→TO
) so that the flow rate q by the water circulation pump is approximately equal to
By determining , it is possible to make the temperature difference between each terminal of the exhaust gas and the circulating supply water at the entrance and exit of the preheating section of the exhaust gas economizer almost the same S゛. The inlet temperature of the feed water, T, is the lowest allowable temperature that can prevent sulfuric acid corrosion of the exhaust gas economizer tube (approximately 130 to 140
℃).

Therefore, the heat recovery rate of exhaust gas can be improved while taking prevention of sulfuric acid corrosion into consideration. That is, as shown in FIG. 5, the exhaust gas outlet temperature T in the preheating section 11 of the exhaust gas economizer 1. Or T. '' is determined by the amount of heat absorbed in the preheating section 11, but in the conventional case, the amount of heated water H,
However, the heat recovery rate could not be sufficiently increased. On the other hand, in this embodiment, in addition to the feed water heating amount Hf, the required heat amount H1 for low-pressure steam generation (or hot water heating) becomes the endothermic amount, so while the circulating feed water inlet temperature T remains the same, the exhaust gas outlet Temperature to T. From T. '' and improve the heat recovery rate.
As an example, when the system of the present invention is adopted for a two-stroke diesel engine with a normal output of 18,600 PS, the amount of heat recovered is approximately 12% compared to the conventional system shown in Figure 1.
, it is expected that the output of the turbo generator will increase by 100-100KW.

As described above, according to the present invention, it is possible to prevent sulfuric acid corrosion of the exhaust gas economizer by maintaining the circulating water supply inlet temperature of the exhaust gas economizer above a certain value, and the terminal temperature difference between the exhaust gas outlet temperature and the water supply inlet temperature. can be lowered to the minimum allowable value, thereby increasing the heat recovery rate compared to conventional exhaust gas heat recovery systems.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a conventional exhaust gas heat recovery equipment system, Fig. 2 is a diagram showing temperature changes in each part of an exhaust gas economizer, and Fig. 3 is a diagram showing an exhaust gas heat recovery equipment system of the present invention. , FIG. 4 is a diagram showing a modification of the heat exchange means in FIG. 3, and FIG. 5 is a diagram showing temperature changes in various parts of a conventional exhaust gas economizer and temperature changes in various parts of an exhaust gas economizer according to the present invention. 1...Exhaust gas economizer, 2...Main steam separation drum, 3...Water circulation pump, 4...
...Surface type feed water heater, 5...Low pressure steam generator, 6...Mixing type feed water heater, 7...
... Main water pump, 11 ... Preheating section of exhaust gas economizer, 13 ... Superheating section of exhaust gas economizer, 21 ... Steam turbine, 23 ...
Condenser, 24... Condensate pump, 25...
A type of miscellaneous machine that uses main steam.

Claims (1)

[Claims] 1. Exhaust gas of an internal combustion engine in which water heated by a feed water heater is sequentially supplied to each piping system of a preheating section, a steam section, and a superheating section of an exhaust gas economizer, and superheated steam is recovered from the superheating section. In the heat recovery method, the flow rate and temperature of circulating water to the feed water heater are adjusted so that the temperature difference between the exhaust gas and feed water at the inlet of the steam section and the temperature difference between the exhaust gas and feed water at the inlet of the preheating section are almost the same. A method for recovering exhaust gas heat from an internal combustion engine, characterized by: 2. An exhaust gas economizer that has piping systems for a preheating section, a steam section, and a superheating section, a water heater that supplies water to the piping system of the exhaust gas economizer, and a main steam that separates steam from the steam and water mixed fluid that exits the exhaust gas economizer. a separation drum; a piping system for supplying at least a portion of the steam separated by the main steam separation drum to a superheating section of an exhaust gas economizer and further sending this to a steam turbine; and a piping system for supplying the steam from the steam turbine to a condenser. In an exhaust gas heat recovery device for an internal combustion engine, comprising a piping system that circulates the condensed water to the feed water heater after condensing it, and a piping system that supplies the condensed water separated by the main steam separation drum to the feed water heater, An exhaust gas heat recovery device for an internal combustion engine, characterized in that a piping system for returning condensed water separated by a main steam separation drum to a feed water heater is provided with flow rate adjustment means and heat exchange means for the condensed water. 3. The exhaust gas heat recovery device for an internal combustion engine according to claim 2, wherein the feed water heater is a mixed feed water heater.