CN111120980B - Cogeneration system and method for realizing efficient waste heat recovery and low nitrogen emission - Google Patents

Cogeneration system and method for realizing efficient waste heat recovery and low nitrogen emission Download PDF

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CN111120980B
CN111120980B CN202010007827.0A CN202010007827A CN111120980B CN 111120980 B CN111120980 B CN 111120980B CN 202010007827 A CN202010007827 A CN 202010007827A CN 111120980 B CN111120980 B CN 111120980B
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flue gas
combustion engine
internal combustion
steam boiler
water
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CN111120980A (en
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刘豪
徐顺塔
涂垚杰
黄璞
王泽安
谢逸豪
罗海华
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Huazhong University of Science and Technology
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Huazhong University of Science and Technology
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B1/00—Methods of steam generation characterised by form of heating method
    • F22B1/02—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers
    • F22B1/18—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers the heat carrier being a hot gas, e.g. waste gas such as exhaust gas of internal-combustion engines
    • F22B1/1807—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers the heat carrier being a hot gas, e.g. waste gas such as exhaust gas of internal-combustion engines using the exhaust gases of combustion engines
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B63/00—Adaptations of engines for driving pumps, hand-held tools or electric generators; Portable combinations of engines with engine-driven devices
    • F02B63/04—Adaptations of engines for driving pumps, hand-held tools or electric generators; Portable combinations of engines with engine-driven devices for electric generators
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02G—HOT GAS OR COMBUSTION-PRODUCT POSITIVE-DISPLACEMENT ENGINE PLANTS; USE OF WASTE HEAT OF COMBUSTION ENGINES; NOT OTHERWISE PROVIDED FOR
    • F02G5/00—Profiting from waste heat of combustion engines, not otherwise provided for
    • F02G5/02—Profiting from waste heat of exhaust gases
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B31/00—Modifications of boiler construction, or of tube systems, dependent on installation of combustion apparatus; Arrangements of dispositions of combustion apparatus
    • F22B31/08—Installation of heat-exchange apparatus or of means in boilers for heating air supplied for combustion
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
    • F23J15/00—Arrangements of devices for treating smoke or fumes
    • F23J15/02—Arrangements of devices for treating smoke or fumes of purifiers, e.g. for removing noxious material
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
    • F23L15/00—Heating of air supplied for combustion
    • F23L15/02—Arrangements of regenerators
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E20/00—Combustion technologies with mitigation potential
    • Y02E20/14—Combined heat and power generation [CHP]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E20/00—Combustion technologies with mitigation potential
    • Y02E20/34—Indirect CO2mitigation, i.e. by acting on non CO2directly related matters of the process, e.g. pre-heating or heat recovery
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Abstract

The invention discloses a cogeneration system and a cogeneration method for realizing high-efficiency waste heat recovery and low nitrogen emission, wherein the cogeneration system comprises a gas internal combustion engine, a denitration device, a steam boiler and a cylinder sleeve water heat exchanger, gas fuel in the gas internal combustion engine is combusted to convert heat energy into mechanical kinetic energy and drive a generator to generate electricity, and medium and low temperature flue gas discharged after the gas internal combustion engine is combusted enters the steam boiler through the denitration device; one end of the cylinder sleeve water heat exchanger is connected to the gas internal combustion engine, and the other end of the cylinder sleeve water heat exchanger is connected with a steam boiler flue gas cooler; the denitration device is positioned between the gas internal combustion engine and the steam boiler, the smoke outlet of the gas internal combustion engine is communicated with the smoke inlet of the denitration device, and the smoke outlet of the denitration device is respectively communicated with the combustion improver inlet and the middle-rear smoke inlet of the steam boiler. The invention aims to realize the full recovery of the waste heat generated by the internal combustion engine, improve the comprehensive utilization efficiency of energy and reduce NO simultaneouslyxAnd (4) discharging.

Description

Cogeneration system and method for realizing efficient waste heat recovery and low nitrogen emission
Technical Field
The invention relates to the field of cogeneration technology and energy cascade utilization, in particular to a cogeneration system and a method capable of realizing efficient waste heat recovery and low nitrogen emission.
Background
The distributed natural gas energy realizes cascade utilization of energy through cold, heat, electricity triple generation and other modes, and compared with a traditional centralized energy system, the distributed natural gas energy has the advantages of saving power transmission and distribution investment, improving energy utilization efficiency, flexibly starting and stopping equipment, improving reliability and safety of system energy supply, saving energy, protecting environment and the like. At present, the development of natural gas distributed energy in China is still in a commercial demonstration stage, and co-production and co-supply are mainly realized by adopting a gas turbine power generation coupling steam waste heat boiler combined cycle power generation or a gas turbine coupling waste heat recycling device (such as a waste heat boiler). However, the maturity of autonomous design, manufacture and commercial application of gas turbines in China is not high, and the equipment cost and the operation and maintenance overhaul cost of the gas turbines are high, wherein the equipment cost is about 6000 yuan/kW, and the maintenance cost is about 0.08 yuan/kWh per year; in addition, the cogeneration system of the gas turbine has the problems of relatively low heat and power surplus, insufficient steam, large configuration of the gas turbine, high construction cost, difficult consumption of electric quantity and the like.
Compared with a gas turbine, the natural gas internal combustion engine has the advantages of compact structure, high start-stop speed, various utilization and combination forms of waste heat (including heat sources such as high-temperature flue gas, cylinder jacket cooling water and lubricating oil cooling water), low air supply pressure grade, high power generation efficiency (above about 40 percent), and low initial investment, namely the market price (about 3000 yuan/kW) of the natural gas internal combustion engine is only half of that of the gas turbine, the overhaul period (about 80000h) of the natural gas internal combustion engine is longer than that of the gas turbine (about 50000h), and the overhaul cost of the natural gas internal combustion engine is only half of that of the gas turbine. At present, the main form of combined cold, heat and electricity generation and supply is that a gas internal combustion engine generates electricity to be coupled with a waste heat boiler or a waste heat direct-fired engine supplies heat and cools for users, wherein the heat released by combustion of the gas internal combustion engine mainly comprises output electric energy, tail middle-low temperature flue gas and high-low temperature cylinder sleeve water which carry away heat, and the heat accounts for 40-45%, 20-25% and 15-20% respectively.
The main technical problems existing in the prior art include:
for the existing coupling waste heat recovery system of the gas internal combustion engine, the following two main defects mainly exist:
firstly, the method comprises the following steps: the waste heat recovery and utilization efficiency of the internal combustion engine is low: the power generation efficiency of the gas internal combustion engine is about 40 percent generally, and simultaneously, middle-low grade flue gas (400-. The medium-low temperature flue gas enters a steam waste heat boiler or a lithium bromide absorption refrigerating unit to be recycled, so that heat and cold are supplied to users. It is worth noting that the cooling water of the cylinder sleeve accounts for 40-50% of the total amount of the available waste heat of the internal combustion engine, but the grade is low, the cylinder sleeve is only used for civil use, the value is not high, and finally the heat recovery rate of the water of the cylinder sleeve is low, even the cylinder sleeve is abandoned, so that a great amount of waste heat is wasted.
Secondly, the method comprises the following steps: nitrogen Oxides (NO)x) Emissions are difficult to control: for gas internal combustion engines, the high temperature and high pressure combustion process results in NOxThe emission of (2) is high, and two technical routes are usually adopted for controlling, such as lean burn technology + tail gas Selective Catalytic Reduction (SCR), Methane Oxidation Catalyst (MOC), and particle trap (DPF) technology for respectively controlling NOxMethane (CH)4) Carbon black (Soot), or stoichiometric combustion + flue gas recirculation (EGR) and three-way catalyst (TWC) technologies for NOxCarbon monoxide (CO), Hydrocarbons (HC). For a large-scale gas internal combustion engine power generation system, combustion is usually carried out under a high air-fuel ratio working condition, although the power generation system has advantages in aspects of engine heat load, heat efficiency and the like compared with a theoretical air-fuel ratio route, the tail part is excessively high in oxygen (5-10%) to cause NOxThe original discharge value is as high as 200-500mg/m3While under the condition of adding MOC, more NO is still available2Therefore, in order to strictly control the emission of the gas internal combustion engine, the SCR denitration technology is required, and urea and ammonia are used as reducing agents, so that the denitration efficiency of more than 70 percent is achieved in the range of 300-500 ℃. Although the SCR ammonia method is adopted for denitration treatment, NO in the smoke of the internal combustion engine can be greatly reducedxThe concentration of the ammonia is high, the ammonia leakage is safe, the system is complex, the operation cost is high, and the like, and particularly when the ammonia escape is controlled improperly, secondary pollution can be caused.
In conclusion, the existing gas turbine cogeneration system has the problems of high manufacturing cost, high operation and maintenance cost and incomplete consumption of key technology, and the internal combustion engine cogeneration system has the problems of difficult cylinder liner water waste heat recovery, unfriendly smoke nitrogen oxide control system environment and the like although the investment and operation cost is low; with the continuous development of social economy, the contradiction between energy demand and ecological environment protection is increasingly intensified, and the development of a high-efficiency, flexible and low-nitrogen-emission distributed cogeneration system has important practical significance and considerable social, environmental and economic benefits.
Disclosure of Invention
Aiming at the problems and defects in the prior art, the invention provides a cogeneration system and a cogeneration method for realizing high-efficiency waste heat recovery and low nitrogen emission, aiming at realizing the full recovery of the power generation waste heat of an internal combustion engine, improving the comprehensive utilization efficiency of energy and simultaneously reducing NOxAnd (4) discharging.
Therefore, the invention adopts the following technical scheme:
a cogeneration system for realizing high-efficiency waste heat recovery and low-nitrogen emission comprises a gas internal combustion engine, a denitration device, a steam boiler and a cylinder sleeve water heat exchanger, wherein gas fuel in the gas internal combustion engine is combusted to convert heat energy into mechanical kinetic energy and drive a generator to generate electricity, and medium-low temperature flue gas discharged after the gas internal combustion engine is combusted enters the steam boiler through the denitration device; one end of the cylinder sleeve water heat exchanger is connected to a gas internal combustion engine, and the other end of the cylinder sleeve water heat exchanger is connected with a steam boiler flue gas cooler; the denitration device is positioned between the gas internal combustion engine and the steam boiler, the smoke outlet of the gas internal combustion engine is communicated with the smoke inlet of the denitration device, and the smoke outlet of the denitration device is respectively communicated with the combustion improver inlet and the middle-rear smoke inlet of the steam boiler.
The system further comprises an air preheater, one end of the air preheater is connected to a smoke outlet of the steam boiler, and the other end of the air preheater is connected with the smoke cooler; wherein, the flue gas after the full heat exchange and cooling of air heater and flue gas cooler is introduced into the atmosphere by the chimney.
Further, the air preheater is a heat exchanger for air and flue gas, and the form of the air preheater comprises a shell-and-tube heat exchanger and a vacuum heat pipe type heat exchanger; the flue gas cooler is a heat exchanger for flue gas at the tail part of the boiler and water supply, the cylinder sleeve water heat exchanger is a heat exchanger for cooling water in the cylinder sleeve and water supply for the boiler, and the form of the heat exchanger comprises a shell-and-tube heat exchanger, a plate heat exchanger and a high-efficiency fin condensation type heat exchanger.
Preferably, the air preheater is a vacuum heat pipe type heat exchanger, and the flue gas cooler and the cylinder liner water heat exchanger are high-efficiency fin condensing type heat exchangers.
And the boiler water supply unit is formed by sequentially connecting a water storage tank, a pressurizing water pump and a three-way valve, wherein the three-way valve is a high-pressure three-way valve, and two outlets of the three-way valve are respectively connected with the cylinder sleeve water heat exchanger and the flue gas cooler.
Further, boiler feed water is adopted to absorb low-temperature waste heat of cooling water of the cylinder liner of the internal combustion engine in the cylinder liner water heat exchanger, so that preheating of the boiler feed water is realized; after passing through the denitration device, the flue gas is divided into two paths to enter a steam boiler, wherein one path enters a hearth from a furnace end, namely a burner area of the steam boiler, and the other path enters the hearth from the middle rear part of the steam boiler.
Further, the gas-fired internal combustion engine and the steam boiler adopt hydrocarbon fuels including methane, propane, natural gas, liquefied petroleum gas and alcohols as fuels, and preferably the fuels are natural gas; the combustion improver is air.
Further, the denitration device adopts hydrocarbon micromolecules including methane, ethylene, propane, carbon monoxide and hydrogen as a reducing agent, and simultaneously adopts a catalyst which has a catalytic effect on catalytic reduction of nitrogen oxides (CH-SCR), and active components of the catalyst comprise transition metals Cu, Mn, Fe, Ni and Co, rare earth Ce, La, Nd, In and Y, and noble metals Pd, Pt and Rh.
A combined heat and power generation method for realizing high-efficiency waste heat recovery and low-nitrogen emission utilizes the combined heat and power generation system for realizing high-efficiency waste heat recovery and low-nitrogen emission to realize high-efficiency waste heat recovery and low-nitrogen emission of combined heat and power generation; boiler feed water is adopted to recover heat of cylinder jacket cooling water in the power generation process of the gas internal combustion engine through a cylinder jacket water heat exchanger, a denitration device is adopted to purify flue gas discharged by power generation of the gas internal combustion engine, the flue gas is divided into two paths to be introduced into a hearth of a steam boiler, and nitrogen oxide generation in the steam boiler is reduced while the waste heat of the flue gas of the gas internal combustion engine is recovered.
Further, the method comprises the following steps:
firstly, when a gas internal combustion engine works, converting chemical energy generated during fuel combustion into mechanical energy, converting the mechanical energy into electric energy through a generator, and simultaneously discharging medium-low temperature flue gas and low-temperature cylinder liner water capable of circularly cooling a cylinder liner after combustion;
step two, the medium-low temperature flue gas discharged by the gas internal combustion engine is processed by the denitration device and then is divided into two air flows, one air flow enters the hearth from the burner area and forms weak reducing atmosphere combustion together with the fuel and the air entering the hearth of the steam boiler, the oxygen concentration of the combustion air is reduced, dilution combustion is formed, the generation of nitrogen oxides in the combustion process is effectively inhibited, and meanwhile, the residual NO in the original flue gas of the gas internal combustion engine is promotedxFurther reduction; the other strand is taken as over-fire air and is introduced from the middle rear part of a hearth of a steam boiler, so that the complete combustion of fuel in the boiler is ensured, the concentration of CO in the flue gas is reduced, and the aims of high-efficiency combustion and low-nitrogen emission are fulfilled;
introducing fuel and air into a hearth of a steam boiler, igniting and burning, and performing heat exchange between all the burned flue gas including the flue gas discharged by the gas internal combustion engine from the denitration device and the air and boiler feed water respectively through an air preheater and a flue gas cooler to further reduce the temperature of the discharged flue gas, maximally improving the waste heat recovery degree, and finally introducing the flue gas into the atmosphere through a chimney;
step four, the purified water at the outlet of the water storage tank is pressurized by a pressurizing water pump and then is divided by a three-way valve, one part of the purified water is directly subjected to heat exchange by a flue gas cooler and then is sent to a steam boiler, and the other part of the purified water is subjected to heat exchange by a cylinder sleeve water heat exchanger to recover the waste heat of the cylinder sleeve cooling water, is further subjected to heat absorption and temperature rise by the flue gas cooler and then is sent to the steam boiler to be heated and;
step five, when the heat load of the steam boiler rises or the heat load of the gas internal combustion engine falls, the heat exchange quantity of cooling water of a cylinder sleeve of the gas internal combustion engine falls at the moment, the boiler is adjusted to continuously feed water through a frequency converter, the boiler water feed quantity passing through a water heat exchanger of the cylinder sleeve is reduced, the boiler water feed quantity directly passing through a flue gas cooler is increased, and the sensible heat and the latent heat of the flue gas are fully absorbed as much as possible;
sixthly, 10-30% of flue gas volume coming out of the denitration device enters a hearth from a burner area of the steam boiler; the rest 70-90% of the flue gas enters the hearth from the middle rear part of the hearth of the steam boiler;
and seventhly, automatically detecting the temperature, the fuel, the air and the smoke components in the operation process of the whole system, and realizing the high-efficiency steady-state operation of the whole system through a dynamic automatic control technology.
Compared with the prior art, the invention has the beneficial effects that:
(1) the system organically combines the internal combustion engine power generation system and the steam boiler system to form a new internal combustion engine-steam boiler cogeneration system, simultaneously adopts boiler feed water to recover the waste heat of cylinder sleeve water, utilizes the heat exchange devices at the hearth and the tail part of the boiler to recover the waste heat of flue gas of the internal combustion engine, and has the advantage that the heat efficiency is obviously improved (10-30%) compared with a single internal combustion engine power generation system.
(2) The system adopts hydrocarbon fuel such as natural gas and the like as a reducing agent to reduce nitrogen oxides generated by combustion of the internal combustion engine, and the hydrocarbon fuel can be used as fuel of the internal combustion engine and a steam boiler, so that a field fuel gas source can be directly used as the reducing agent, related ammonia equipment does not need to be additionally arranged, and the problems of corrosion, leakage, escape, secondary combustion pollution and the like of ammonia storage, transportation and use in the ammonia process of SCR catalytic denitration can be effectively avoided. Even if the carbon-hydrogen reducing agent is excessively used in the denitration device, the carbon-hydrogen reducing agent can be combusted in the steam boiler, so that the problem of fuel waste is solved.
(3) When the engine is running at a low load or under non-ideal operating conditions, a portion of unburned CO, hydrocarbons (CH) may be producedi) Soot, etc., which unburned hydrocarbons in gaseous or solid form may likewise be used as reducing agent for NO in a denitration devicexReduction removal is carried out, and meanwhile, the residual part can enter a boiler hearth to be completely combusted, so that secondary pollution and energy waste can not be caused.
(4) The method uses a low-nitrogen combustion technology combining flue gas dilution combustion and air staged combustion in a steam boiler system, can reduce the air excess coefficient of a combustor area, simultaneously ensures that unburned fuel is further reacted completely at the middle rear part of a hearth, and realizes controllable oxygen content and concentration of the tail part of the integral boiler flue gasSimultaneously achieve CO and NOxLow emission effect. The specific explanation is as follows: the smoke generated by the power generation and combustion of the internal combustion engine contains 5-10% of oxygen and high-concentration CO2、H2O and N2Wherein, the oxygen in the flue gas can be used as an oxidant to replace part of the air of the steam boiler; CO in flue gas2、H2O and N2Can be used as a diluting medium to play a role of recycling flue gas outside the conventional boiler, so that the oxygen concentration in the reaction zone is reduced; thereby reducing NO in the boiler furnacexCreating conditions for the generation of the product. In further detail, a small part (10-30%) of combustion flue gas of the denitrated internal combustion engine enters a boiler hearth from a steam boiler combustor and a nearby area of the steam boiler combustor and participates in combustion of a front area of the hearth, and due to dilution of the flue gas, the oxygen concentration of a combustion reaction area is reduced, so that the flame temperature is reduced, and thermal NO is inhibitedxGeneration of (1); on the other hand, the (90-70%) denitration combustion flue gas of the internal combustion engine is injected from the middle rear part of the boiler furnace, oxygen in the flue gas is used as a supplementary combustion oxidant, so that the fuel in the boiler furnace is promoted to be burnt out, meanwhile, the air surplus coefficient of the front area of the boiler furnace is favorably reduced, the front area of the boiler furnace is kept in a weak reducing atmosphere, and NO is further inhibited during combustionxWhile favoring the generation of residual NOxIs reduced by hydrocarbon small molecules.
(5) The system relates to energy output and waste heat recovery and utilization in various forms, particularly integrates various combination modes such as flue gas waste heat and latent heat recovery of a boiler, waste heat recovery of cylinder sleeve water and the like, and is flexible and changeable. When the internal combustion engine is in high load and the boiler is in low load operation, the flow direction proportion of boiler feed water is adjusted through the three-way valve, the feed water flow flowing to the cylinder sleeve water heat exchanger is increased, meanwhile, the feed water flow directly entering the flue gas cooler is reduced, and the high-efficiency recovery of the waste heat of the cylinder sleeve water is ensured; on the contrary, when the internal combustion engine is in low load and the boiler is in high load operation, reverse regulation is carried out, and efficient recovery of the tail flue gas waste heat of the boiler is ensured.
(6) The invention realizes the power generation and the steam generation, realizes the recovery of the waste heat of the flue gas and the cylinder sleeve water and the gradient utilization of heat energy through the coupling of the internal combustion engine power generation system and the steam boiler system, realizes the low emission of nitrogen oxides through the carbon hydrogen catalytic denitration of the flue gas outside the boiler and the low nitrogen combustion technology in the boiler, realizes the effect of low oxygen dilution combustion by replacing the recirculated flue gas outside the boiler by the flue gas of the internal combustion engine in a series connection mode, and is a novel high-efficiency and low-emission combined heat and power system.
Drawings
Fig. 1 is a schematic structural composition diagram of a cogeneration system with high-efficiency waste heat recovery and low nitrogen emission provided by the invention.
Fig. 2 is a schematic structural composition diagram of a variation of the cogeneration system with high efficiency waste heat recovery and low nitrogen emissions provided by the present invention.
Description of reference numerals: 1. a gas internal combustion engine; 2. a denitration device; 3. a steam boiler; 4. an air preheater; 5. a flue gas cooler; 6. a chimney; 7. a cylinder liner water heat exchanger; 8. a three-way valve; 9. a pressurized water pump; 10. a water storage tank; 11. a generator; 12. an economizer.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings and specific embodiments, which are provided for illustration only and are not to be construed as limiting the invention.
In the following detailed description, unless otherwise specifically noted, terms used herein shall be understood as having the meaning as commonly used in the art. The various devices, materials, instruments, etc. used in the present invention may be commercially available or may be prepared by existing methods.
In the description of the present invention, it is to be particularly emphasized that the terms "one end", "the other end", and the like indicate positions or orientations based on the positional or orientation relationships shown in the drawings, and are only for convenience of describing the present invention, and do not particularly denote specific orientations.
Example one
As shown in fig. 1, a cogeneration system capable of realizing efficient waste heat recovery and low nitrogen emission mainly comprises a gas internal combustion engine 1, a denitration device 2 and a steam boiler 3, wherein the gas internal combustion engine 1 is provided with a fuel inlet, an air inlet and a flue gas outlet, the denitration device 2 is provided with a flue gas inlet and outlet, and the steam boiler 3 is provided with a fuel inlet, an air inlet, a feed water inlet, a middle and rear flue gas inlet, a steam outlet and a tail flue gas outlet;
the natural gas is used as fuel, and the gas internal combustion engine 1 is ignited and started to drive the generator 11 to operate and supply power to the outside. The temperature of flue gas generated after natural gas is combusted in the gas internal combustion engine 1 is 400 ℃, the oxygen content in the flue gas is 8%, the water inlet temperature of circulating water for cooling a cylinder sleeve in the power generation process of the internal combustion engine is 80 ℃, and the water outlet temperature is 90 ℃. The stable operation of the power generation system of the internal combustion engine is realized by online monitoring and control of various operation parameters such as online smoke temperature, water temperature, fuel flow, air flow, electric power and the like.
The method comprises the steps of feeding flue gas generated after natural gas is combusted in a gas internal combustion engine 1 into a denitration device 2 arranged between a flue gas outlet of the gas internal combustion engine 1 and an inlet of a combustor of a steam boiler 3, adopting a hydrocarbon SCR denitration catalyst taking iron-based metal/oxide as a main active substance, spraying the natural gas according to the amount of 1-10 times of NO concentration to realize reduction denitration, and feeding the flue gas discharged from the denitration device 2 into a steam boiler 3 system in two ways through a pipeline, wherein 20% of the flue gas is directly mixed with combustion-supporting air entering the steam boiler 3, and the rest 80% of the flue gas is directly fed into the tail part of a boiler hearth (about 1/3 of the whole length of.
The combustor of the steam boiler 3 is a staged combustion low-nitrogen combustor, natural gas is used as fuel, the natural gas is fed into a fuel channel of the low-nitrogen combustor by means of the pressure of a natural gas pipeline, an air feeder is used for feeding air into an air channel of the combustor through an air preheater 4, the denitration flue gas with the amount as described above is mixed before the air is fed into the combustor, the oxygen concentration in combustion air is reduced, and stable combustion is realized after ignition. The automatic combustion monitoring and controlling technology is adopted in the boiler system to measure the combustion temperature and the smoke component (O) in real time2CO and NO), fuel quantity, air temperature, total water supply quantity, water quantity flowing through cylinder liner water heat exchanger 7, water quantity directly entering flue gas cooler 5, and water of each pathTemperature, preheating air temperature, furnace outlet smoke temperature, air preheater 4 outlet smoke temperature, flue gas cooler 5 outlet smoke temperature, steam flow, steam pressure and steam temperature; the high-efficiency steady-state operation of the system is realized through automatic feedback control.
A water storage tank 10, a pressure water pump 9 and a three-way valve 8 are adopted to form a boiler water supply unit, the boiler water supply unit realizes a continuous water supply process through a frequency conversion regulator, wherein the three-way valve 8 is a high-pressure three-way valve, two outlets of the three-way valve are respectively connected with a cylinder sleeve water heat exchanger 7 and a flue gas cooler 5, the purpose of the continuous water supply is that one part of water is directly subjected to heat exchange through the flue gas cooler 5 and then is sent to a steam boiler 3, and the other part of water is firstly subjected to waste heat recovery of cylinder sleeve cooling water through the cylinder sleeve water heat exchanger 7 and then is sent to the steam boiler 3 for heating. One end of the cylinder sleeve water heat exchanger 7 is connected to the gas internal combustion engine 1, and the other end is connected with the flue gas cooler 5. The total amount of the boiler water supply and the water supply proportion of the water entering the cylinder sleeve water heat exchanger 7 and the flue gas cooler 5 are adjusted, so that the temperature of the cooling water entering and exiting the cylinder sleeve of the internal combustion engine is kept in a normal working range, and meanwhile, the normal operation working condition parameters of the steam boiler 3 are maintained.
The flue gas that discharges after boiler furnace burning preheats the air through air heater 4, and air heater 4 is the vacuum heat pipe form, and air heater 4 one end is connected to steam boiler 3's exhanst gas outlet, and the other end is connected with flue gas cooler 5, and afterwards, the flue gas that comes out from air heater 4 is further cooled in flue gas cooler 5, and flue gas cooler 5 is high-efficient fin condensation heat exchanger, transmits waste heat to boiler feed water simultaneously, and the low temperature flue gas (110-50 ℃) after abundant heat transfer cooling is introduced into the atmosphere by chimney 6.
When the heat load of the steam boiler 3 is increased or reduced, and the heat load or the electric load of the gas combustion engine 1 is increased or reduced, optimization is performed on the basis of a thermodynamic equilibrium model of the whole internal combustion engine power generation-steam boiler system and machine learning of operation big data according to the highest thermal efficiency and the minimum pollutant emission of the system, optimal operating condition parameters under new output targets (thermoelectric ratio, steam and electric quantity) are determined, and presetting-monitoring-feedback regulation is performed through subsystems of the internal combustion engine power generation and the steam boiler, so that efficient and stable operation of the whole system is guaranteed.
Example two
As a partial modification of the invention, as shown in fig. 2, the flue gas cooler 5 in fig. 1 is split into the flue gas cooler 5 and the economizer 12 in fig. 2, by changing 1 feedwater-flue gas heat exchanger into 2 feedwater-flue gas heat exchangers, essentially without change; for another example, it is within the scope of the present invention to interchange the positions of the air preheater 4 and the economizer 12 of FIG. 2 back and forth without any substantial change.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and scope of the present invention are intended to be covered thereby.

Claims (8)

1. A cogeneration method for realizing high-efficiency waste heat recovery and low-nitrogen emission utilizes a cogeneration system for realizing high-efficiency waste heat recovery and low-nitrogen emission to realize high-efficiency waste heat recovery and low-nitrogen emission of cogeneration, the cogeneration system for realizing high-efficiency waste heat recovery and low-nitrogen emission comprises a gas internal combustion engine (1), a denitration device (2), a steam boiler (3) and a cylinder sleeve water heat exchanger (7), and is characterized in that: gas fuel in the gas internal combustion engine (1) is combusted to convert heat energy into mechanical kinetic energy and drive the generator (11) to generate electricity, and medium-low temperature flue gas discharged after combustion of the gas internal combustion engine (1) enters the steam boiler (3) through the denitration device (2); one end of the cylinder sleeve water heat exchanger (7) is connected to the gas internal combustion engine (1), and the other end is connected with the steam boiler flue gas cooler (5); the denitration device (2) is positioned between the gas internal combustion engine (1) and the steam boiler (3), the smoke exhaust outlet of the gas internal combustion engine (1) is communicated with the smoke inlet of the denitration device (2), and the smoke outlet of the denitration device (2) is respectively communicated with the combustion improver inlet and the middle-rear smoke inlet of the steam boiler (3);
boiler feed water is adopted to recover heat of cylinder jacket cooling water in the power generation process of the gas internal combustion engine (1) through a cylinder jacket water heat exchanger (7), a denitration device (2) is adopted to purify flue gas discharged by power generation of the gas internal combustion engine (1), the flue gas is introduced into a hearth of a steam boiler (3) in two ways, and nitrogen oxide generation in the boiler of the steam boiler (3) is reduced while the flue gas waste heat of the gas internal combustion engine (1) is recovered;
the method comprises the following steps:
the method comprises the following steps that firstly, when a gas internal combustion engine (1) works, chemical energy generated when fuel is combusted is converted into mechanical energy, the mechanical energy is converted into electric energy through a generator (11), and meanwhile, medium-low temperature flue gas and low-temperature cylinder liner water capable of circularly cooling a cylinder liner are discharged after combustion;
step two, the medium-low temperature flue gas discharged by the gas internal combustion engine (1) is processed by the denitration device (2) and then is divided into two air flows, one air flow enters the hearth from the burner area and forms weak reducing atmosphere with the fuel and air entering the hearth of the steam boiler (3) for combustion, the oxygen concentration of combustion-supporting air is reduced, dilution combustion is formed, the generation of nitrogen oxides in the combustion process is effectively inhibited, and meanwhile, the further reduction of residual NOx in the original flue gas of the gas internal combustion engine (1) is promoted; the other strand is taken as over-fire air and is introduced from the middle rear part of a hearth of a steam boiler (3), so that the complete combustion of fuel in the boiler is ensured, the concentration of CO in the flue gas is reduced, and the aims of high-efficiency combustion and low-nitrogen emission are fulfilled;
introducing fuel and air into a hearth of a steam boiler (3), igniting and burning the fuel and the air, and performing heat exchange between all the burned flue gas including the flue gas discharged by a gas internal combustion engine (1) from a denitration device (2) and the air and boiler feed water respectively through an air preheater (4) and a flue gas cooler (5) to further reduce the temperature of the discharged flue gas, maximally improving the waste heat recovery degree, and finally introducing the flue gas into the atmosphere through a chimney (6);
step four, the purified water at the outlet of the water storage tank (10) is pressurized by a pressurizing water pump (9) and then is divided by a three-way valve (8), one part of the purified water is directly subjected to heat exchange by a flue gas cooler (5) and then is sent to a steam boiler (3), and the other part of the purified water is subjected to waste heat recovery of cylinder sleeve cooling water by a cylinder sleeve water heat exchanger (7), is further subjected to heat absorption and temperature rise by the flue gas cooler (5) and then is sent to the steam boiler (3) for heating to generate steam;
step five, when the heat load of the steam boiler (3) rises or the heat load of the gas combustion engine (1) falls, the heat exchange quantity of cooling water of a cylinder sleeve of the gas combustion engine (1) falls, continuous water supply of the boiler is adjusted through a frequency converter, the boiler water supply quantity passing through a cylinder sleeve water heat exchanger (7) is reduced, the boiler water supply quantity directly passing through a flue gas cooler (5) is increased, and the sensible heat and the latent heat of the flue gas are fully absorbed as much as possible;
step six, 10-30% of flue gas volume coming out of the denitration device (2) enters a hearth from a burner area of a steam boiler (3); the rest 70-90% of the flue gas enters the hearth from the middle rear part of the hearth of the steam boiler (3);
and seventhly, automatically detecting the temperature, the fuel, the air and the smoke components in the operation process of the whole system, and realizing the high-efficiency steady-state operation of the whole system through a dynamic automatic control technology.
2. The cogeneration method of claim 1, wherein said method comprises the steps of: the combined heat and power generation system for realizing high-efficiency waste heat recovery and low-nitrogen emission also comprises an air preheater (4), wherein one end of the air preheater (4) is connected to a flue gas outlet of the steam boiler (3), and the other end of the air preheater is connected with a flue gas cooler (5); wherein, the flue gas after the full heat exchange and temperature reduction of the air preheater (4) and the flue gas cooler (5) is introduced into the atmosphere through a chimney (6).
3. A cogeneration method with efficient waste heat recovery and low nitrogen emissions according to claim 2, characterized in that: the air preheater (4) is a heat exchanger for air and flue gas, and the form of the air preheater comprises a shell-and-tube heat exchanger and a vacuum heat pipe type heat exchanger; the flue gas cooler (5) is a heat exchanger for flue gas at the tail part of the boiler and water supply, the cylinder sleeve water heat exchanger (7) is a heat exchanger for cooling water in the cylinder sleeve and water supply for the boiler, and the form of the heat exchanger comprises a shell-and-tube heat exchanger, a plate heat exchanger and a high-efficiency fin condensation type heat exchanger.
4. A cogeneration method with high efficiency waste heat recovery and low nitrogen emissions according to claim 3, characterized in that: the air preheater (4) is a vacuum heat pipe type heat exchanger, and the flue gas cooler (5) and the cylinder sleeve water heat exchanger (7) are high-efficiency fin condensation type heat exchangers.
5. The cogeneration method of claim 1, wherein said method comprises the steps of: the combined heat and power generation system for realizing high-efficiency waste heat recovery and low-nitrogen emission further comprises a boiler water supply unit which is sequentially connected with a water storage tank (10), a pressurizing water pump (9) and a three-way valve (8), wherein the three-way valve (8) is a high-pressure three-way valve, and two outlets of the three-way valve are respectively connected with a cylinder sleeve water heat exchanger (7) and a flue gas cooler (5).
6. The cogeneration method of claim 5, wherein said method comprises the steps of: boiler feed water is adopted to absorb the low-temperature waste heat of cooling water of the cylinder liner of the internal combustion engine in the cylinder liner water heat exchanger (7), so that the preheating of the boiler feed water is realized; after passing through the denitration device (2), the flue gas is divided into two paths to enter the steam boiler (3), one path enters a hearth from a furnace end, namely a burner area, of the steam boiler (3), and the other path enters the hearth from the middle rear part of the steam boiler (3).
7. A cogeneration method with high efficiency waste heat recovery and low nitrogen emissions according to any one of claims 1-6, characterized in that: the gas internal combustion engine (1) and the steam boiler (3) adopt hydrocarbon fuels including methane, propane, natural gas, liquefied petroleum gas and alcohols as fuels, and the combustion improver is air.
8. A cogeneration method with high efficiency waste heat recovery and low nitrogen emissions according to any one of claims 1-6, characterized in that: the denitration device (2) adopts hydrocarbon micromolecules including methane, ethylene, propane, carbon monoxide and hydrogen as a reducing agent, and simultaneously adopts a catalyst which has a catalytic action on catalytic reduction of nitrogen oxides by hydrocarbon, and active components of the catalyst comprise transition metals Cu, Mn, Fe, Ni and Co, rare earth Ce, La, Nd, In and Y and noble metals Pd, Pt and Rh.
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