RU2607118C2 - Method and system for deep heat recovery of boiler combustion products of thermal power plants - Google Patents

Abstract

FIELD: energy.

SUBSTANCE: invention relates to station power, particularly, to energy saving during operation of boilers power stations, comprising steam-turbine plants (STP). Method for deep recovery comprises feeding STP condensate into water-gas heat exchanger (WGH) at boiler outlet and heating condensate using heat of combustion products (CP), combustion products (WGH) are cooled to temperature below dew point by (5–10) °C, obtained condensate (OC) is collected, purified according to a known technology and fed into a condensate line and then successively into condensate heater, deaerator and boiler. In order to implement method, deep recycling system (DR) includes arranged under water-gas heat exchanger (WGH) condensate drain tank (OC), condensate collection and storage tanks, drain and condensate pumps, as well as condensate treatment sections, connected to condensate line of station.

EFFECT: besides saving heat (fuel) present solution reduces emission of toxic oxides NO_x and CO₂ due to suppression with water vapour, reducing fuel consumption, obtaining additional water, which can be used for boiler makeup and other needs, eliminates or minimises condensation in gas path and stack, improving maintenance conditions, avoiding need for flue gas recirculation for preventing condensation.

2 cl, 4 dwg

Description

The invention relates to station power, and more particularly to technology for the deep utilization of heat of combustion products (PS) of gas boilers of steam turbine power plants.

Known methods and systems for the deep utilization, GU, heat of substation boilers, providing for deep cooling of substation in water-gas heat exchangers (VGT) to a temperature below the dew point Т _Р and condensation of water vapor generated in substation as a result of burning fuel (hydrogen, hydrocarbons) and contained in air [1, 2]. Cold water is used as a cooler - for example, tap water going to the hot water supply, boiler feed water, etc. (AA Kudinov. Energy conservation in heat generating installations. M., Mechanical Engineering, 2012) [1]. Such a water-gas heat exchanger is essentially a surface utilization condensing heat exchanger. The heat exchanger is installed at the outlet of the boiler - in the tail surfaces or in the duct, at the junction with the boiler. Described in [2] (E. Shadek, B. Marshak, I. Krykin, V. Gorshkov. Condensing heat exchanger-heat exchanger - modernization of boiler plants. “Industrial and heating boiler houses and mini-TPPs”, 5 (26) 2014) installation (with AHT in the boiler flue) can be considered as an analog.

GI systems based on heat pump technologies are known, namely absorption bromide lithium refrigerating machines (ABHM) or heat pumps, ABTN (E. Shadek, B. Marshak, A. Anokhin, V. Gorshkov. Deep heat recovery of waste gases from heat generators. 2 (23) 2014) [3]. In such systems, the heat exchanger is included in the closed refrigeration circuit of the ABHM or ABTN evaporator, in which cooling water circulates with a temperature below the dew point. Such systems do not have practical prospects in view of the large capex, the need for a cooling tower and large areas.

The dew point temperature for PS natural gas is 50-55 ° C. Reliable condensation requires cooling of the PS to a temperature of about 40 ° C.

The condensate temperature of a steam turbine is, as a rule, within the range of 20-35 ° C, which, when supplied to the high-temperature cylinder, allows the substrates to be cooled to the required 40 ° C, to provide condensation of the water vapor contained in them, i.e. deep disposal

As a prototype, a method has been adopted to utilize the heat of substation boilers of steam turbine power plants by heating the condensate due to the heat of combustion products, comprising supplying condensate from a steam turbine condenser to a water-gas heat exchanger (VGT) located at the boiler outlet, heating the condensate and cooling the combustion products in this heat exchanger, supply of heated condensate to the condensate line and then sequentially to the deaerator and boiler (PA Berezinets, GG Olkhovsky. Promising technologies and power plants for the production of heating and electric energy. Section six. 6.2 gas-turbine and combined-cycle plants. 6.2.2. Combined-cycle plants. VTI. Modern environmental technologies in the energy sector. Information collection edited by V. Ya. Putilov. MPEI Publishing House. 2007 (prototype) [4].

The water-gas heat exchanger (VGT) is located at the outlet of the station boiler, in the convective tail heating surfaces, this is the so-called gas condensate heater (GPC).

From the condensate collector of the turbine’s condenser, the condensate is sent (sometimes through a block desalting plant, BOW) to the water-gas heat exchanger, and from it to the condensate heaters and deaerator in series. With standard quality condensate, the BOW can be bypassed.

To prevent condensation of water vapor from the PS at the last pipes of the VGT, the temperature of the condensate in front of it is maintained at least 60 ° C by means of recirculation of heated condensate to the inlet,

In the known method, the temperature of the PS at the outlet of the heat exchanger is above the dew point, namely, when the condensate is heated to 60 ° C, the temperature of the PS behind the condensate heat exchanger is in the range not lower than 70-80 ° C.

Thus, in the solution prototype PS is cooled in a heat exchanger to a temperature above the dew point temperature in the range of 15-30 ° C.

To further reduce the PS temperature, a water-to-water heat exchanger (VVTO), cooled by make-up water of the heating system, is included in the condensate recirculation line. Mains water is heated in the gas-condensate condensate. Using VVTO allows more deep cooling of PS. With additional gas cooling of 10 ° C in each boiler, you can get about 3.5 Gacl / h of heating load.

The purpose of the invention is improving thermal efficiency (fuel economy, increasing efficiency), reducing toxic emissions from substations, obtaining excess water for recharge and other needs, improving the service conditions and durability of the gas path.

This goal is achieved by the fact that in the proposed method, the products of combustion (PS) in a water-gas heat exchanger (CGT) are cooled to a temperature below the dew point by (5-10) ° C, the condensate obtained from the products of combustion is collected, subjected to purification by known technology and sent sequentially condensate heater, deaerator and boiler.

To implement the proposed method, a system for deep heat recovery is proposed, comprising a condensate discharge tank under the gas-water heat exchanger, condensate collection and storage tanks, drainage and condensate pumps, as well as a condensate treatment section connected to the condensate line.

Possible options for placing the AHT behind the boiler, while maintaining the essence and claims:

- in the lining of the boiler itself - in the composition of the tail surfaces as the last section along the PS in the convection shaft, as a condensation economizer;

- in the flue, at the junction with the boiler.

The proposed solution is illustrated by the example of a system with the installation of a water-gas heat exchanger in the boiler flue.

In FIG. 1 is a flow diagram of a station based on a cogeneration turbine with steam extraction and a condensate regenerative heating system; in FIG. 2-4 - a deep utilization unit — a water-gas heat exchanger in a gas duct of a boiler with a bypass channel: FIG. 2 is a longitudinal section with a fragment of the boiler, FIG. 3 is a cross-sectional view of a chamber with AHT; FIG. 4 - section in plan.

In the drawings are indicated:

- in FIG. 1: 1 - a station steam boiler, 2 - a burner, 3 - a chamber for a heat exchanger, 4 - a water-gas heat exchanger, VGT, 5 - a droplet eliminator, 6 - a tray and a tank for draining condensate of combustion products, 7 - a gas path, 8 - a tank of contaminated condensate 9 - a drainage pump, 10 - a condensate reserve tank, 11 - a condensate pump, 12 - a condensate flow regulator, 13 - a condensate purification section of combustion products (chemical water treatment), 14 - a steam turbine with steam extraction, 15 - a reduction cooling unit, ROW, 16 - condenser, 17 - condensate collector, 18 - deaerator, 19 - itatelny pump, 20 - collecting condensate tank vapor 21 - manifold 22 - heater high pressure condensate LDPE, 23 - block demineralizer, BOU, 24 - heater Low pressure condensation of IPA, 25 - a drain pump, 26 - boiler pump.

In FIG. 2-4: 27 - the tail of the boiler, 28 - the overlap of the heat exchanger chamber, a removable cover, 29 - the safety valve, 30 - the shutoff valve, 31, 32 - the return and direct lines of the VGT, 33 - the check valve, 34 - the smoke exhaust, 35 - a chamber for placement of a deep utilization unit, 36 - an adjustment throttle valve (gate, damper) with an actuator, 37 - a bypass channel.

The bypass channel is separated from the working space of the chamber by a dividing wall, which makes the design as compact as possible.

Installation of a droplet eliminator is optional (according to the operating conditions of the unit).

As can be seen from the diagram of FIG. 1, steam condensate from the condensate collector 17 under the pressure of the condensate pump 11 is fed into the collection tank 20 and into the condensate collector 21. From there, the condensate is sent to the block desalination plant (BOW) 23. From the BOW, part of the incoming condensate is fed to the inlet of the high-pressure tank, and the other part the condensate line of the station, in this scheme - to the PND 24, and from there using the drain pump 25 to the deaerator 18. A mode is possible when all the condensate from the BOU 23 is sent to the VGT 4 and, after passing through the GU unit - 4, 6, 8, 13 - served on PND 24 and in the deaerator 18.

Heated condensate from VGT 4 is fed into the condensate line and sequentially to deaerator 18, from it to the boiler, through LDPE 22. The condensate of the combustion products obtained in VGT 4 is poured into the sump and reservoir 6, and from there into the contaminated condensate tank 8 and pumped by drainage pump 9 into the condensate storage tank 10, and from it the condensate pump 11 through the flow regulator 12 is fed to the condensate cleaning section 13, where the PS condensate is processed (cleaned) by a known technology. The purified condensate PS is fed to the PND 24 and then to the deaerator 18.

Condensate PS of natural gas is of high quality and needs simple and inexpensive processing - decarbonization (not always) and degassing. Condensate flow is regulated by regulator 12. From deaerator 18, pure condensate is fed by feed pump 19 to LDPE 22 and then to the boiler.

For neutralization (chemical treatment) of condensate in small volumes, it is recommended to use replaceable dolomite fillers (blocks with granulate), and for large ones, containers with dosing devices for caustic soda (liquid neutralization devices) (BOSCH Thermotechnics company)

AHT is installed in the chamber 35 at the junction of the boiler 27 with the gas duct (Fig. 2-4).

In order to prevent vapor condensation in the gas path and chimney, bypassing is used, i.e. the bypass of part of the hot gases in addition to the VGT through the bypass channel (37) with the control throttle valve (36). The temperature of the gas mixture behind the VGT during bypassing is usually maintained within the range of 70 (in summer) - 90 ° C (in winter). In summer, if there is no danger of condensation, they work without bypass.

Various types of heat exchangers are applicable as heat exchangers — shell and tube, straight pipe, with knurled fins, plate or the most efficient design with a new form of heat transfer surface with a small bending radius (RG-10 regenerator SPC “Anode”), etc. Other designs are considered: 1. heat-exchange block sections based on a bimetallic air heater of the VNV123-412-50ATZ brand (OJSC “Calorifer Plant”, Kostroma) 2. collapsible apparatus of the GEA Mashimpeks company or all-welded GEABloc type stainless steel plate heat exchangers characterized by high efficiency and compactness.

The material of the heat exchanger - corrosion-resistant steels and alloys, aluminum pipes, fins, polymer coatings, etc. The flue, chamber, gas path is made of corrosion-resistant materials, coatings, in particular stainless steels, plastics - this is a common practice.

The amount of condensate supplied from the collector 21 to the VGT, and accordingly its heat load is determined by technical, economic, design considerations, taking into account the operational parameters of the boiler, the capabilities and conditions of the technological scheme of the station.

The temperature of the flue gases of the boilers usually in the range of 110-130 ° C allows heating the condensate in the VGT before the deaerator to the required 90-100 ° C. Thus, the technology’s temperature requirements are satisfied: both condensate heating (about 90 ° C) and PS cooling to condensation (up to 40 ° C).

The increase in aerodynamic drag of the gas path is compensated by a decrease in PS volumes due to the removal of water vapor and condensate discharge, as well as a decrease in fuel consumption.

In GI, physical heat and heat of vaporization are utilized, the boiler efficiency in the condensation mode is about 105% in terms of lower heat of combustion, Q ^P _H [2, 3].

The effectiveness of this solution is revealed in comparison with the existing system with GPC as the closest analogue and competitor.

Taking for a calculation example a boiler with N _К = 10 MW / 8.6 Gcal / h the initial data: α = 1.25, temperature: behind the boiler, before the HPP T _УХ = 130 ° C, for the HPP T ₂ = 80 ° C, boiler efficiency η _K2 = 0,92, Q _P ^H = 8000 kcal / m ^3, the gas flow rate _C = 8,6 × ¹⁰ June / 8000 × 0,92 = 1,168 m ³ / h, the proportion W v and the total volume of PS : v = 13.1 m ³ / m ³ , W = V _Г × v = 1168 × 13.1 = 15300 m ³ / h. The amount of heat utilized in the CCP: q _CCP = C × W × ΔT, where C is the heat capacity of the PS, kcal / m ³ д deg. We get: q _HPA = 0.33 × 15300 × (130-80) = 0.252 Gcal / h / 294 kW. Next, assuming the numerous calculations and experimental data, the amount of heat to disposal at SU, ie a VGT, Q _GUT equal to 11% of N _K, Q obtain _VGT = 0.11 N _K = 0,11 × 8, 6 = 0.946 Gcal / h / 1100 kW.

The gain in heat savings from replacing the CCP on the proposed unit GU (0.946-0.252) = 0.694 Gcal / h / 807 kW. With a power utilization factor for a power plant boiler equal to KIM = 0.7, this will save 532,000 m ^{3 of} gas per year, or about 2.7 million rubles. at a price of 5 rubles / m ³ . Savings increase in proportion to the value of Q _GUT (and boiler capacity).

When condensate is heated by ΔТ = 90-30 = 60 ° С, its consumption in a heat exchanger with a thermal power of 4 MW will be about 57 t / h (for this calculation model).

In the proposed system, there is no need for VVTO to further reduce the temperature of the flue gases. Cooling at least 30 ° C will give an additional 3.5 Gcal / h × 3 = 10.5 Gcal / h of heating load (or save this amount of heat).

The operation of the GU system, replacing the CCP in the known scheme, does not reduce the share of electricity in the total combined generation of heat and electric energy at the CHPP and does not affect the overall efficiency of the station.

The solution provides multiple effects. In addition to energy conservation, with deep disposal:

- harmful emissions of oxides of CO _X and NO _{X are} reduced due to reduced fuel consumption, but mainly, suppression of toxicity in the presence of water, irrigation of PS with drop moisture;

- obtaining additional, excess water, which after treatment can be used to feed the boiler and other needs of the station;

- condensation is localized in one place - in the VGT. In addition to insignificant mudguard after the droplet eliminator, condensation in the gas path and the associated corrosive effects of moisture, the formation of ice in the duct and especially in the chimney are excluded;

- there is no need for recirculation - mixing part of the hot gases to the cooled or heated condensate to the cold in order to increase the temperature of the outgoing substations to prevent condensation in the gas path and chimney (saving energy, money).

Claims (2)

1. A method for the deep utilization of heat of products of combustion of boilers of power plants, comprising supplying condensate from a steam turbine condenser to a water-gas heat exchanger (VGT) located at the outlet of the boiler, heating the condensate and cooling the products of combustion in this heat exchanger, supplying heated condensate to the condensate line and sequentially to a deaerator and a boiler, characterized in that in order to increase the thermal efficiency of the technological scheme of the station and save fuel, increase efficiency, reduce the emission of toxic oxides NO _X and CO ₂ , obtaining additional water due to condensation of water vapor contained in the combustion products, improving the service conditions and durability of the gas path, the combustion products (PS) in a water-gas heat exchanger are cooled to a temperature below the dew point by (5-10) ° C, and the resulting in this heat exchanger condensate from the combustion products is collected, subjected to purification by known technology and sent sequentially to the condensate heater, deaerator and boiler. 2. The deep heat recovery system for implementing the method according to claim 1, characterized in that it contains a condensate discharge tank under the water-gas heat exchanger, condensate collection and storage tanks, drainage and condensate pumps, as well as a condensate treatment section connected to the condensate line.

Images