RU2747899C1 - Flue gas heat recovery unit - Google Patents

Abstract

FIELD: energy.

SUBSTANCE: invention relates to the field of energy. The waste heat exchanger of flue gases contains a water heat exchanger-waste-heat exchanger connected with a condensate collector and an inlet line of a steam boiler, equipped with a water treatment unit at the inlet. The inlet of the heat exchanger-utilizer, designed to heat the flow of untreated water to a temperature below the deposition of salts - calcium and magnesium carbonates, is communicated with the source of untreated water, and the outlet - with the inlet of the water treatment plant through an adjustable flow divider, which ensures the connection of a part of the water flow with condensate of flue gases in proportions of at least three to one. It also contains a heat pump that reduces the temperature of the heated water flow by 1-2°С. In this case, the heat pump heats the mixture of water and condensate, pumped by the water pump in the heat pump at a speed of at least 2 m / s, to the temperature of salt formation - calcium and magnesium carbonates, before entering the condensate trap. The outlet of the condensate collector is connected to the outlet of the water treatment plant and is equipped with water pH sensors and reagent dispensers to regulate it and exclude salt deposition in the boiler, and its bottom is with a salt collector. The condensate trap is equipped with a carbon dioxide outlet at the top.

EFFECT: invention allows reducing the deposition of salts - magnesium and calcium carbonates and energy consumption.

1 cl, 1 dwg

Description

The invention relates to recuperative installations and can be used in heat power engineering, oil refining, petrochemical, chemical and other industries for utilization of flue gas heat.

Known recuperator installation (patent for PM RU No. 175713, IPC F24H 8/00, publ. 12/15/2017 Bull. No. 35), containing a flare tube with burners and means for introducing waste gases and air located in the lower part of the flare tube, product heater with flue gases, and the flare tube is equipped with a pipeline installed in its upper part for removing flue gases, which is connected by means of a branch pipe with the annular space of the product heater, at the outlet of which a smoke exhauster is installed for pumping out flue gases from the flare tube, while on the pipeline for exhausting flue gases, a rotary damper is installed to regulate the temperature of the heated product.

The disadvantages of this installation are the need for additional heating of flue gases with subsequent cooling, which requires additional consumption of fuel and electricity to pump a much larger amount of liquid heated in the heat exchanger, and the lack of collection and disposal of condensate.

Also known is a pipe-in-pipe heat exchanger (patent for PM RU No. 181266, IPC F28D 07/10, F28D 07/06, publ. 09.07.2018 Bull. No. 19), consisting of several series-connected tubular elements formed by two concentrically located external and internal pipes, and rolls connecting the internal pipes, while the free ends of each inner pipe and roll are threaded and interconnected by a coupling with centering elastic plates evenly spaced on its lateral surface, and each roll is installed inside the knee, and the knee is made in the form of a corrugated pipe made of an elastic material, the corrugations of which form a helical line, and the inner diameter of the corrugations D ₁ and the outer diameter of the bead d obey the ratio:

D ₁ / d = 1.15 ÷ 1.25,

where D ₁ is the inner diameter of the corrugation D ₁ , m;

d is the outer diameter of the roll d, m.

The disadvantages of this installation are the need for large sections for sufficient cooling of flue gases, which leads to a high metal consumption and the removal of large production areas for implementation, and the lack of collection and disposal of condensate.

The closest is a combined cycle plant with deep utilization of waste gas heat (patent RU No. 2700843, IPC F01K 25/08, publ. 09/23/2019 Bull. No. 27), containing:

a gas turbine unit including a gas turbine, a multistage turbocharger, a combustion chamber and an electric generator;

a steam waste heat boiler with a gas path equipped with dampers and a chimney,

a steam turbine unit consisting of a steam turbine with a condenser equipped with a condensate collector, an electric generator, a cooling tower in the condenser circuit and pumps - feed, circulation and condensate;

condensing heat exchanger for waste heat recovery,

wherein the inlet of the heat exchanger is connected to the condensate collector of the steam turbine condenser, and the outlet is connected to the condensate supply line from the condensate collector of the steam turbine condenser to the waste heat boiler.

The disadvantages of this installation are the need for additional heating of the exhaust gases with subsequent cooling, which requires additional fuel and electricity costs to pump a much larger amount of liquid heated in the heat exchanger, and the lack of control over the condensate pH during collection and disposal of the condensate, which can lead to a premature exit from building installations in the interaction of acid with metal and / or precipitation of magnesium and / or calcium carbonates on the walls.

The technical task of the proposed technical solution is to create a design for a heat exchanger for boiler flue gases, which allows a heat pump to heat condensate, which is directed to the outlet of the water treatment system, which saves energy and fuel, while separating magnesium and calcium carbonates with subsequent control of water pH.

The technical problem is solved by a waste heat exchanger of flue gases, which includes a water heat exchanger-waste heat exchanger connected with a condensate collector and an inlet line of a steam boiler equipped with a water treatment unit at the inlet.

What is new is that the inlet of the heat exchanger-utilizer, designed to heat water to a temperature below the deposition of salts - calcium and magnesium carbonates, is communicated with the source of untreated water, and the outlet - with the inlet of the water treatment plant through an adjustable flow divider, which ensures the connection of a part of the flow with the condensate of the flue gas gases in a ratio of at least three to one. The heat exchanger contains a heat pump that reduces the temperature of the heated water flow by 1-2 ° C and heats the mixture of water and condensate pumped by the water pump in the heat pump at a speed of at least 2 m / s to the temperature of salt formation - calcium and magnesium carbonates before entering into the condensate collector, the outlet of which is connected to the outlet of the water treatment plant and is equipped with water pH sensors and reagent dispensers to regulate it and exclude salt deposition in the boiler, and the bottom with a salt collector, while the condensate collector is equipped with a carbon dioxide outlet on top.

Another novelty is that the condensate trap and its piping are covered with heat-insulating material.

The drawing shows a diagram of a heat exchanger.

The waste heat exchanger of flue gases passing through the chimney 1 includes a water heat exchanger-waste heat exchanger 2, communicated with the condensate collector 3 and the inlet line 4 of the steam boiler 5, equipped at the inlet with a water treatment unit 6. Inlet 7 of the heat exchanger-waste heat exchanger 2, intended for heating to a temperature below the sediment salts - calcium and magnesium carbonates (recommended not higher than 45 ° C), communicated with a source of untreated water (not shown), and outlet 8 - with the inlet of the water treatment plant 6 through an adjustable flow divider 9 (for example, a tee with an adjustable valve), providing a connection parts of the flow of water with flue gas condensate in a ratio of at least three to one (at least three parts of water to one part of condensate leaving heat exchanger-heat exchanger 2). The heat exchanger contains a heat pump 10, which reduces the temperature of the flow of heated water by 1-2 ° C, while heating the mixture of water and condensate, pumped by the water pump 11 in the heat pump 10 at a speed of at least 2 m / s, to the temperature of formation of insoluble in water salts - mostly calcium and magnesium carbonates (above 55 ° C), before entering the condensate trap 3.

The high flow rate of the mixture of water and condensate in the heat pump 10 provides a high value of the Reynolds number, determined by the formula:

, [1]

, [one]

where Re is the Reynolds number;

V - fluid flow rate, m | s;

L - characteristic linear size (for pipes - diameter d), m;

(- kinematic viscosity of the liquid, m ² / s.

At very large values of the Reynolds number, it is believed that the effect of viscosity manifests itself in the part of the flow that moves in the immediate vicinity of the surface and is called the boundary layer. With an increase in the Reynolds number, the turbulization of the boundary layer increases and its thickness decreases; therefore, at very high Reynolds numbers, it is possible to achieve a boundary layer thickness close to zero. In the absence of vaporization in the boundary layer, the intensity of the formation of primary scale is the release of insoluble substances (deposition of primary scale due to the decomposition of bicarbonates, a decrease in solubility when heating some salts (sulfates) and due to the formation of hardly soluble substances due to the concentration of salts during evaporation during the formation of microscopic particles of steam in the boundary layer. layer) also becomes close to zero. The formed and released insoluble particles in the heat pump 10 are carried away by the flow, since the boundary layer is practically absent. All this together significantly increases the turnaround period and the service life of the heat pump 10. The outlet 12 of the condensate collector 3 is connected to the outlet 13 of the water treatment plant 6 and is equipped with water pH sensors 14 and reagent dispensers 15 for its regulation and exclusion of scale deposits in the boiler 5, and the bottom with a pipeline 16 with a salt collector (not shown) for discharging salts formed in the heat pump 10 and washed away. The condensate collector 3 is equipped on top with an outlet 17 for carbon dioxide released during the formation of salts and decomposition of carbonic acid under the action of an elevated temperature in the heat pump 10. To reduce heat losses, the condensate collector 3 and its piping (not shown) are covered with heat insulating material (not shown).

The authors do not pretend to the design of the heat exchanger-utilizer 2, boiler 5, water treatment plant 6, flow divider 9 and heat pump 10, since they can be of any design known from open sources and satisfying the requirements for the operability of these elements.

Structural elements, process connections, valves and piping of elements that do not affect the performance of the heat exchanger are not shown in the drawing or are shown conditionally.

The heat exchanger of flue gases works as follows.

Untreated water of the volume required for the operation of the boiler 5 is pumped by the pump 18 to the inlet 7 of the heat exchanger-heat exchanger 2 and then through the heat exchanger-heat exchanger 2, the flow divider 9, the heat pump 10 and the inlet line 4 to the water treatment plant 6. In the water treatment plant 6, the water is purified and softened (freed from water-soluble hydrocarbons) and pumped 19 into the steam boiler 5, where it heats up during the combustion of fuel (associated or natural gas, fuel-air mixture, coal with an oxidizer, and / or the like) to a vaporous state. From the boiler 5, steam is supplied through the steam line 20 to consumers (for example, for heating layers during the production of a high-viscosity mixture, heating workshops, home and / or the like - not shown). When fuel is burned in boiler 5, smoke is formed (with a temperature of 120-240 ° C - it varies from the type of boiler and the fuel used), which is discharged through the chimney 1 through the heat exchanger-heat exchanger 2. Heat exchanger-heat exchanger 2 at the design stage is selected so that the flowing through it, untreated water was heated to a temperature that excludes salt deposits inside the heat exchanger-utilizer 2, thereby significantly increasing its overhaul period and service life. At the same time, the smoke in the heat exchanger-utilizer 2 is also cooled to a temperature below the "dew point" (practically the temperature of the smoke is reduced to the ambient temperature). As a result, condensate is formed containing water and carbonic acid, which is taken from the heat exchanger-utilizer 2 and, together with a part of the stream of untreated water from the flow divider 9, is fed to the pump inlet 11.

To ensure maximum efficiency without "flow disruptions" (capture of the evolved air due to the created vacuum by pump 11, which can lead to its failure), the following correspondence must be observed at the inlet of pump 11:

[2]

[2]

where Q _n - pump capacity, m ³ / s;

q _to - the volume of released condensate per unit of time, m ³ / s;

q _in - the volume of part of the water per unit time, directed from the flow divider 9, m ³ / s.

As practice has shown, to avoid "stalling" at the inlet of pump 11, the following inequality must be observed:

, [3]

, [3]

where q _to - the volume of released condensate per unit of time, m ³ / s;

q _in - the volume of part of the water per unit time, directed from the flow divider 9, m ³ / s.

To comply with the conditions [1] and [2], at the outlets of the heat exchanger-waste heat exchanger 2 and the flow divider 9, the corresponding flow meters 21 and 22 are installed, the signals from which are sent to the control unit 23. The control unit 23 regulates by means of the flow divider 9: which part of the flow direct untreated water together with condensate to the pump inlet 11.

The water heated in the heat exchanger-utilizer 2 from its outlet 8 through the divider 9 is supplied to the heat pump 10, where its temperature slightly decreases (by 1-2 ° C), after which in a warm form (usually with a temperature of 25-35 ° C) the inlet line 4 is supplied to the water treatment plant 6. As a result, the purification and softening of water in the water treatment plant 6 is facilitated, which significantly saves the energy spent on this.

Pump 11 at a speed of at least 2 m / s pumps a mixture of water and condensate in the heat pump 10, which in it, due to the extraction of heat from untreated water, is heated to the temperature of formation of water-insoluble salts (in practice, to a temperature of 80-95 ° C), together with which the mixture is sent to the condensate collector 3. In the condensate collector 3, the released salts are deposited at the bottom, from where it is periodically taken through the pipeline 16 to the salt collector and further for disposal, and the released carbon dioxide accumulates at the top, from where the 17 is taken for disposal. The mixture of water purified from salts and carbon dioxide from the condensate collector 3 enters outlet 12, in which its pH is measured by pH sensors of water 14, if the acidity parameter declared by the technologists does not correspond to the pH sensors of water 14, a signal is sent to the reagent dispensers 15, which adds the reagent (aqueous solution soda, acid, corrosion inhibitor and / or the like) into the mixture to adjust its pH accordingly. A hot mixture of water and condensate (usually with a temperature of 80 ± 5 ° C) from the condensate collector 3 through outlet 12 is connected to warm water (usually with a temperature of 30 ± 5 ° C) at outlet 13 from the water treatment plant 3, increasing the total temperature of the water supplied by the pump 19 to boiler 5. Thus, reducing the cost of heating water to the vapor state in the boiler 5.

As practice has shown, the costs of installations for heating water to a vaporous state without using heat recovery from flue gases is 10-15% higher than when using the proposed heat exchanger. Also, compared to installations using heat recovery to heat water to a vaporous state, but without using a heat pump, energy costs, including fuel, are 3-5% higher than when using the proposed heat exchanger.

The proposed heat exchanger for boiler flue gases allows a heat pump to heat condensate with water, which are sent to the outlet of the water treatment system, which saves energy and fuel, while separating magnesium and calcium carbonates with subsequent control of water pH.

Claims (2)

1. Utilizer of flue gas heat, including a water heat exchanger-utilizer, communicated with a condensate collector and an inlet line of a steam boiler, equipped at the inlet with a water treatment plant, characterized in that the inlet of a heat exchanger-utilizer designed to heat the stream of untreated water to a temperature below the deposition of salts - carbonates calcium and magnesium, communicated with the source of untreated water, and the outlet - with the inlet of the water treatment plant through an adjustable water flow divider, which ensures the connection of a part of the water flow with flue gas condensate in a ratio of at least three to one; water by 1–2 ° С and heating a mixture of water and condensate, pumped by a water pump in a heat pump at a speed of at least 2 m / s, to the temperature of salt formation - calcium and magnesium carbonates before entering the condensate collector, the outlet of which is connected to the outlet of the water treatment plant and is equipped with a sensor water pH gauges and reagent dispensers for its regulation and exclusion of salt deposition in the boiler, and its bottom - with a salt collector, while the condensate collector is equipped with a carbon dioxide outlet on top. 2. The waste heat exchanger of flue gases according to claim 1, characterized in that the condensate collector and its piping are covered with heat-insulating material.

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