CN102777240A - Diesel engine exhaust gas waste heat recovery system of two-stage Rankine cycle - Google Patents

Abstract

The invention discloses a two-stage Rankine cycle diesel engine exhaust waste heat recovery system. The technical solution is: a first evaporator, a first steam turbine, a high temperature side of a high temperature preheater, a first condenser and a first working fluid The pumps are connected in sequence to form the first-stage Rankine cycle system; the second evaporator, the second steam turbine, the second condenser, the second working fluid pump, the low-temperature preheater and the low-temperature side of the high-temperature preheater are connected in sequence to form the second stage. Rankine cycle system. The two-stage Rankine cycle system is connected through a high-temperature preheater. The exhaust pipe of the engine is connected to the gas side of the first and second evaporators in turn, and the cooling water in the engine is connected to the working medium side in the low-temperature preheater, forming a closed cycle heat exchange of the cooling water in the engine. The steam turbines in the two stages are respectively connected with generators. The exhaust waste heat is recovered through the steam and organic two-stage Rankine cycle, so that the high-temperature exhaust waste heat of the engine can be fully utilized, and the purpose of energy saving and efficient thermal cycle of the system can be achieved.

Description

Two-stage Rankine Cycle Diesel Engine Exhaust Heat Recovery System

technical field

The invention belongs to the technology of energy saving and emission reduction of internal combustion engines, and in particular relates to a two-stage organic Rankine cycle system for recovering waste heat from high-temperature exhaust of diesel engines.

Background technique

With the increasing shortage of energy and the increasingly severe environmental problems, the energy saving and emission reduction of internal combustion engines has attracted worldwide attention. The use of organic Rankine cycle (ORC) technology to recover waste heat from diesel engines is a current research hotspot, with high thermal efficiency and safety and simple structure. At present, most of the waste heat recovery technologies of the Rankine cycle are concentrated in a single-stage cycle. Through the research, it is found that the recovery of medium and low temperature waste heat using single-stage ORC is more efficient than the traditional steam Rankine cycle. However, the condition for using ORC is that the temperature of the working fluid is generally not higher than 350°C, and the exhaust temperature of the engine is generally as high as 500-600°C. Such a high temperature may cause the decomposition of organic working fluid, which is the main defect restricting the recovery and utilization of high-temperature waste heat in ORC. In order to solve this problem, the University of Parma in Italy adopted heat transfer oil circulation between the exhaust gas and the working fluid, and conducted a simulation analysis of this scheme, and the results showed that the efficiency can be increased by 12%. However, the heat transfer oil circulation will reduce the grade of the heat source and reduce the recovered heat. In addition, the single-stage ORC does not fully utilize the exhaust waste heat. The exhaust gas of the engine still has a relatively high temperature after heat exchange, and the exhaust gas after the expansion of the working medium also has a relatively high temperature, including the cooling water also has a certain amount of waste heat. .

Therefore, in view of the above current situation, if the high-temperature waste heat of engine exhaust can be fully recovered and utilized, it will be of great significance to the improvement of energy-saving and emission-reduction technology of internal combustion engines.

Contents of the invention

The object of the present invention is to propose a diesel engine exhaust waste heat recovery system adopting two-stage Rankine cycle, which recovers the exhaust waste heat of the engine step by step, so that the high-temperature exhaust waste heat of the engine can be fully utilized.

The principle and system composition of the present invention will be described below in conjunction with the accompanying drawings. Two-stage Rankine cycle diesel engine exhaust waste heat recovery system, including evaporator, steam turbine, generator, condenser, working medium pump, high temperature preheater, low temperature preheater and engine, etc. The technical scheme adopted by the system is: the working fluid side of the first evaporator, the first steam turbine, the high temperature working fluid side of the high-temperature preheater, the working fluid side of the first condenser, and the first working fluid pump are sequentially connected to form the first stage Rankine cycle system; from the working medium side of the second evaporator, the second steam turbine, the working medium side of the second condenser, the second working medium pump, the working medium side of the low temperature preheater and the low temperature working medium side of the high temperature preheater in sequence The connection forms the second-stage Rankine cycle system. The first and second Rankine cycle systems are connected through a high temperature preheater. The exhaust pipe of the engine is connected to the gas side of the first evaporator and the second evaporator in turn, and the cooling water in the engine is connected to the working medium side of the low-temperature preheater to form a closed cycle heat exchange of the cooling water in the engine. The first steam turbine is shaft-connected to the first generator; the second steam turbine is shaft-connected to the second generator.

The principle of the system is: the first-stage Rankine cycle is a steam Rankine cycle, and the working medium used is water. The heat source of the first-stage Rankine cycle is the high-temperature waste heat of the engine exhaust, and the steam cycle system is used to drive the engine to generate electricity. The heat source of the second-stage Rankine cycle is mainly the high temperature exhaust gas from the engine after a heat exchange (with the first evaporator). The organic Rankine cycle suitable for medium and high temperature heat sources can be used, thereby realizing the full utilization of the exhaust waste heat of the diesel engine, and achieving the goals of energy saving and high-efficiency thermodynamic cycle of the system.

The characteristics and beneficial effects of the present invention are that the steam Rankine cycle and the organic Rankine cycle are used to make full use of the high-temperature exhaust waste heat of the engine. The exhaust waste heat of the engine can be recovered through the two-stage Rankine cycle step, which can relieve the limitation of ORC technology on the recovery of exhaust waste heat of the diesel engine, and achieve the purpose of energy saving and efficient thermal cycle of the system.

Description of drawings

Shown accompanying drawing is the principle of the invention and the composition structure diagram of the system. Thick lines in the figure indicate exhaust paths.

Detailed ways

The principle and system of the present invention will be further described below in conjunction with the accompanying drawings and through embodiments. It should be noted that this embodiment is illustrative rather than restrictive, and does not limit the protection scope of the present invention.

Two-stage Rankine cycle diesel engine exhaust heat recovery system, including evaporator, steam turbine, generator, condenser, working medium pump, high temperature preheater, low temperature preheater and engine, the system is composed of: the first evaporator The working medium side of the device 1, the first steam turbine 2, the high-temperature working medium side of the high-temperature preheater 3, the working medium side of the first condenser 4, and the first working medium pump 5 are sequentially connected to form a first-stage Rankine cycle system; The working medium side of the second evaporator 7, the second steam turbine 8, the working medium side of the second condenser 9, the second working medium pump 10, the working medium side of the low temperature preheater 11, and the low temperature working medium side of the high temperature preheater 3 in sequence The connection forms the second-stage Rankine cycle system. The first steam turbine is connected with the first generator 6 shafts; the second steam turbine is connected with the second generator 12 shafts. The first and second Rankine cycle systems are connected through the high-temperature preheater 3, and the exhaust pipe of the engine 13 is connected to the gas side of the first evaporator and the second evaporator in sequence. The cooling water in the engine is connected to the working fluid side in the low-temperature preheater to form a closed cycle heat exchange of the cooling water in the engine.

The working medium described in the first Rankine cycle is water. The working fluid described in the second Rankine cycle is R123 or R134a.

Its system cycle is: the high-temperature exhaust gas of the engine comes out from the exhaust pipe and enters the first evaporator, exchanges heat with the water in the evaporator, makes it evaporate into saturated (or superheated) high-temperature and high-pressure gas, and enters the first steam turbine to do work , to drive the first generator to generate electricity. The exhaust gas discharged from the first steam turbine enters the high-temperature preheater, and the organic working medium in the second-stage Rankine cycle performs (heating) heat exchange, and then enters the first condenser to exchange heat with external cooling water to become liquid. Liquid water enters the first evaporator through the first working fluid pump, and continues to the next (steam) Rankine cycle. The high-temperature exhaust gas discharged from the first evaporator enters the second evaporator, exchanges heat with the organic working fluid in the evaporator, and discharges the low-temperature exhaust gas into the surrounding environment after heat exchange.

In the second-stage Rankine cycle system, the working fluid passes through the second working fluid pump, and first preheats with the low-temperature preheater (with the cooling water circulating in the engine); then the high-temperature preheater (with the first steam turbine condenses ) for the second preheating; after the second preheating, the organic circulating working fluid enters the second evaporator (with the sub-high temperature engine exhaust on the flue gas side of the first evaporator) for heat exchange, making it saturated (or Superheated) high-temperature and high-pressure gas enters the second steam turbine to do work and drive the second-stage generator to generate electricity. The exhaust gas discharged from the second steam turbine enters the second condenser and is cooled to liquid by external cooling water. Then the liquid organic working medium enters the low-temperature preheater again through the second working medium pump to continue the next organic Rankine cycle. As an example, the working fluid used in the second Rankine cycle is R123.

Claims (3)

1. Two-stage Rankine cycle diesel engine exhaust waste heat recovery system, including evaporator, steam turbine, generator, condenser, working medium pump, high-temperature preheater, low-temperature preheater and engine, characterized by: the first The working medium side of the evaporator (1), the first steam turbine (2), the high temperature preheater (3) the high temperature working medium side, the first condenser (4) working medium side and the first working medium pump (5) are connected in sequence The first-stage Rankine cycle system; the first steam turbine is connected to the shaft of the first generator (6), and the working medium side of the second evaporator (7), the second steam turbine (8), and the second condenser (9) are used side, the second working fluid pump (10), the working fluid side of the low-temperature preheater (11), and the low-temperature working fluid side of the high-temperature preheater (3) are connected in sequence to form a second-stage Rankine cycle system. The second steam turbine and The shaft of the second generator (12) is connected, and the first and second Rankine cycle systems are connected through the high-temperature preheater (3), and the exhaust pipe of the engine (13) is connected to the first evaporator and the second evaporator in sequence On the gas side of the engine, the cooling water in the engine is connected to the working medium side in the low-temperature preheater to form a closed cycle heat exchange of the cooling water in the machine. 2. The diesel engine exhaust waste heat recovery system with two-stage Rankine cycle according to claim 1, characterized in that the working medium in the first-stage Rankine cycle is water. 3. The diesel engine exhaust waste heat recovery system with two-stage Rankine cycle according to claim 1, characterized in that the working fluid in the second-stage Rankine cycle is R123 or R134a.

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