GB2114727A

GB2114727A - Process and apparatus for drying flue gases and increasing the draught in furnaces

Info

Publication number: GB2114727A
Application number: GB08203984A
Authority: GB
Inventors: Vinzenz Siller
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-02-11
Filing date: 1982-02-11
Publication date: 1983-08-24
Also published as: GB2114727B

Abstract

The apparatus comprises two heat exchangers 3, 4 connected in series to the waste heat flue 12 through which the flue gas flows. For reducing the flue gas temperature in a furnace to the dew point, the process comprises cooling the flue gas to below the dew point and separating the steam and impurities contained in the flue gas in heat exchanger 3, and heating the purified flue gas in heat exchanger 4 to provide a natural draught in the chimney (not shown). A heat exchanger 10 is provided for e.g. preheating water for industrial uses. In use, a liquid flows in circuit 9 firstly through heat exchanger 4 and then through heat exchanger 3. <IMAGE>

Description

SPECIFICATION Process and apparatus for drying flue gases and increasing the draught in furnaces The invention relates to a process for drying flue gases and increasing draughts in furnaces and to an apparatus for performing this process.

For the purpose of increasing the efficiency of furnaces it is known to remove so much energy from the flue gases that the glue gas temperature is only slightly above the dew point. However, and particularly in preponderantly partial load operation, there is a risk of dropping below the dew point and as a result the water contained in the flue gas condenses and damages the chimney. There is also a risk of the upward pressure in the chimney no longer being sufficient for removing the flue gas through the chimney by natural draught, so that unless a boiler with an overpressure burner is used, additional measures such as the use of a chimney fan or a special induced draught are necessary.

The problem of the invention is to reduce the flue gas temperature in furnaces to the dew point by using a suitable flue gas drying process without flue gas condensate being produced in the chimney and/or draught aids being required for flue gas removal both under full load and partial load operating conditions. In addition, an apparatus is to be provided enabling the process to be performed.

According to the invention this problem is solved in that the flue gas leaving the furnace is cooled to below the dew point in a first heat exchanger and steam and impurities contained in the flue gas are separated and in a second heat exchanger the purified flue gas is heated again to such an extent that the flue gas leaving the second heat exchanger forms a natural draught in the chimney due to its own upward pressure, the heated cooling water leaving the first heat exchanger wholly or partly circulating through the second heat exchanger and optionally acts on a further heat exchanger for preheating the water for industrial uses or the like.

The problem of the application is also solved by an apparatus for performing the process, wherein there are provided two series-connected heat exchangers through which flow the flue gas, the outlet pipe connection of the heat exchanger battery of the first heat exchanger in the flue gas flow direction is connected to the inlet pipe connection of the heat exchanger battery of the second heat exchanger and its outlet pipe connection is connected to the inlet pipe connection of the heat exchanger battery of the first heat exchanger, a heat exchanger for preheating water for industrial uses or the like being arranged in the flow circuit formed by the connecting lines between the inlet pipe connection and the outlet pipe connection.

The invention is described in greater detail hereinafter relative to non-limitative embodiments and with reference to the attached drawings, wherein show: Fig. 1 a diagrammatic view of a flue gas cooling apparatus.

Fig. 2 a diagrammatic view of another embodiment of a flue gas cooling apparatus.

Apparatus 1 in Fig. 1 has two heat exchangers 3, 4, which are connected in series to the waste heat flue 12. The first heat exchanger 3 is used for cooling the flue gas from the furnace to below dew point, so that the steam and impurities contained in the flue gas 2 are separated here.

The condensate is discharged through a condensate discharge connection 26. In the following heat exchanger 4, the flue gas from which the seam and impurities have been removed is heated to such an extent that there is a natural draught in the following chimney due to the upward pressure of the flue gas. However, as a function of the boiler system used, this need not necessarily be sufficient to overcome the resistances on the flue gas side, because an overpressure burner or fan can optionally be used for this purpose.

Apparatus 1 is particularly suitable for flue gases, which enter heat exchanger 3 at high temperatures of 1 80 to 2500C and even higher.

A flow circuit 9 is provided for performing the process. The inlet pipe connected by means of a pipeline to the outlet pipe connection 8 of heat exchanger 4. Outlet pipe connection 5 of heat exchanger 3 is operatively connected by means of a pipeline to the inlet pipe connection 6 of heat exchanger 4. For this purpose a three-way valve 1 6 is provided in the pipeline connected to the outlet pipe connection 5, one outlet of said valve being connected as a bypass line 1 5 to the further three-way valve 1 7 joined to the pipeline connected to the inlet pipe connection 6. The free outlets of the three-way valves 1 6, 1 7 are connected by means of connections 1 3, 14 to a heat exchanger 10, which can e.g. be used for preheating water for industrial uses.To permit a liquid circulation in flow circuit 9, a circulating pump 23 is provided, which can be arranged between three-way valve 1 7 and inlet pipe connection 6. An after-heater 11 is provided in bypass line 1 5 for after-heating the heating water entering heat exchanger 4 via inlet pipe connection 6 for the purpose of heating the flue gas. This after-heater 11 can be constructed as an electrical radiator, a heat exchanger subject to the action of boiler water or a heat exchanger arranged in the waste heat flue 12 between the heat exchanger 3 and the furnace.

As the operating states in heat exchangers 3, 4 can be varied as a function of the flue gas inlet temperature and the flue gas steam content and the flue gas outlet temperature at heat exchanger 4 necessary for a natural draught, a regulating or control system is provided for optimizing operation. A regulator 20 is connected by means of control lines to the control elements 1 8, 1 9 of three-way valves 16, 17. Each heat exchanger 3, 4 contains on the outlet side a sensor 21,22 connected by a measured value transmission line 25 to the regulator. By measuring the operating states in heat exchangers 3, 4 the valve positions required on three-way valves 1 6, 1 7 are adjusted by means of the regulator.

Fig. 2 shows an apparatus 1 a, which is particularly suitable for flue gases 2 entering the first heat exchanger 3 at relatively low temperatures. In the flow circuit 9a of apparatus 1 a, three-way valve 1 6 is arranged in the supply line to the inlet pipe connection 7 and three-way valve 1 7 in the line connected to outlet pipe connection 8. A bypass 15 is once again provided between the two three-way valves 1 6, 1 7, while the other valve outlets are connected to a heat exchanger 10 via connections 13, 14.

After-heater 11 is located in line 28 connecting outlet pipe connection 5 of heat exchanger 3 to inlet pipe connection 6 of heat exchanger 4. It is possible to construct line 28 in such a way that after-heater 11 can be constructed as a heat exchanger for positioning in the waste heat flue 12. Line 28 also contains a throttle valve 11, which permits an adjustment of the flow quantity.

Preferably the throttle valve is constructed as a solenoid valve. The three-way valves 16, 1 7 may also be constructed as solenoid valves. The control means corresponds to those used in the case of apparatus 1.

Advantageously heat exchanger 3 is made from corrosion-resistant material, so that the acids produced during the separation of the condensate do not lead to premature damage to the heat exchanger 3 and consequently to apparatus 1, 1 a.

Heat exchangers 3, 4 of apparatus 1, 1 a can also be arranged horizontally in the chimney. Heat exchangers 3, 4 are then preferably positioned at the bottom of the chimney. Heat exchangers 3, 4 can also be integrated into a unit, preferably a base unit of a unit-type chimney comprising prefabricated parts. This reduces constructional expenditure when installing boiler plants.

Claims

1. A process for drying flue gases and increasing the draught in furnaces, wherein the flue gas leaving the furnace is cooled to below the dew point in a first heat exchanger and steam and impurities contained in the flue gas are separated and in a second heat exchanger the purified flue gas is heated again to such an extent that the flue gas leaving the second heat exchanger forms a natural draught in the chimney due to its own upward pressure, the heated cooling water leaving the first heat exchanger wholly or partly circulating through the second heat exchanger and optionally acts on a further heat exchanger for preheating the water for industrial uses or the like.

2. A process according to claim 1, wherein the heated cooling water leaving the first heat exchanger is heated to a higher temperature than the flue gas entering the second heat exchanger in an after-heater and prior to entering the second heat exchanger.

3. A process according to claims 1 and 2, wherein the heat exchanger for preheating the water for industrial uses or the like is subject to the action of the heating water from the first heat exchanger or the heating water from the second heat exchanger.

4. An apparatus for performing the process according to claim 1 to 3, wherein there are provided two series-connected heat exchangers through which flow the flue gas, the outlet pipe connection of the heat exchanger battery of the first heat exchanger in the flue gas flow direction is connected to the inlet pipe connection of the heat exchanger battery of the second heat exchanger and its outlet pipe connection is connected to the inlet pipe connection of the heat exchanger battery of the first heat exchanger, a heat exchanger for preheating water for industrial uses or the like being arranged in the flow circuit.

formed by the connecting lines between the inlet pipe connection and the outlet pipe connection.

5. An apparatus according to claim 4, wherein an after-heater is located between the outlet pipe connection of the first heat exchanger and the inlet pipe connection to the second heat exchanger.

6. An apparatus according to claim 5, wherein the after-heater is constructed as a heat exchanger exposed to the action of the heating water, water for industrial uses, etc.

7. An apparatus according to claim 5, wherein the after-heater is constructed as an electrical radiator.

8. An apparatus according to claim 5, wherein the after-heater is constructed as a heat pump.

9. An apparatus according to claim 5, wherein the after-heater is constructed as a heat exchanger located in the waste heat flue between the furnace and the first heat exchanger.

10. An apparatus according to any one of the claims 4 to 9, wherein a bypass line is positioned between the connections of the heat exchanger for preheating the water for industrial uses or the like and parallel to said heat exchanger, said bypass line being connected to the connections by three-way valves.

11. An apparatus according to claim 10, wherein the three-way valves have control elements connected to a regulator operatively connected to a sensor associated in each case with one heat exchanger.

12. An apparatus according to any one of the claims 4 to 11, wherein the flow circuit formed between the outlet pipe connection of the first heat exchanger and the inlet pipe connection of the second heat exchanger is constructed as a closed circuit in which is arranged a circulating pump.

1 3. An apparatus according to any one of the claims 4 to 12, wherein the heat exchangers are arranged horizontally in the chimney associated with the furnace.

1 4. An apparatus according to claim 13, wherein the heat exchangers are integrated into a unit of a unit-type chimney.

1 5. A process for drying flue gases as claimed in Claim 1 and substantially as herein described.

1 6. Apparatus for effecting the process of Claim 1 substantially as herein described with reference to the accompanying drawings.