GB2234689A

GB2234689A - Waste gas treatment

Info

Publication number: GB2234689A
Application number: GB8917524A
Authority: GB
Inventors: Robert Singleton; John Edward Andrews
Original assignee: ROSSENDALE ENGINEERING CO Ltd
Current assignee: ROSSENDALE ENGINEERING CO Ltd
Priority date: 1989-08-01
Filing date: 1989-08-01
Publication date: 1991-02-13
Also published as: GB8917524D0

Abstract

Heat recovery apparatus (10) comprises an incinerator (14) which receives contaminated waste gases from industrial process equipment (12). The waste gases are heated to a sufficient temperature and for a sufficiently long period of time to remove contaminants and the incinerated waste gases pass either to a waste heat boiler (16) or an air to air heat exchanger (60). The outlet from the waste heat boiler or the air to air heat exchanger flow to a fluidised bed heat exchange apparatus (18) in which is located a counterflow heat exchanger (20). and the cooled waste gases are exhausted to atmosphere. The heat recovery apparatus removes contaminants such as hydrocarbons and halogens from industrial process waste gases and provides a means of recovering the heat from those gases. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO HEAT RECOVERY APPARATUS This invention relates to heat recovery apparatus. The invention is particularly, though not exclusively, applicable to utilising the waste heat from industrial processes together with a fluidised bed heat exchanger, to provide for the removal of contaminants from the carriers of the industrial process waste heat.

Many industrial processes discharge combustion products and other gases containing contaminants to atmosphere, thereby wasting heat energy and polluting the atmosphere. For example, contaminants, such as hydro-carbons and halogens, which can only be destroyed at high temperatures, are produced in coating processes using all grades of plastics, or protective finishes, such as flame retardants, water proofing, or dyestuffs. Other processes releasing contaminants are paint stoving and food processing, such as bread baking.

The present invention seeks to provide a heat recovery apparatus in which a substantial proportion, if not all of the contaminants in the discharged waste gases from an industrial process are removed from the gases discharged to atmosphere, and which recovers at least some of the heat in the waste gases.

Preferably the waste products from an industrial process are incinerated at sufficient temperatures and for a sufficiently long period of time to substantially remove the volatile contaminants from the waste products, and the discharge from the incinerator is then passed through a fluidised bed in which is located a heat exchanger through which either a fluid is passed so as to recover a proportion of the heat from the discharge from the incinerator.

A recuperator can be provided in the exhaust from the fluidised bed so as to preheat the input of liquid or gas to the heat exchanger located in the fluidised bed, and the cooled waste gases are exhausted to atmosphere.

Also the discharge from the incinerator can be supplied to a waste heat boiler prior to entering the fluidised bed, the waste heat boiler being arranged to receive water and to discharge steam and/ or condensate.

Alternatively, an air to air heat exchanger can replace the waste heat boiler, to heat air for use in the industrial process producing contaminated waste gases.

Accordingly the present invention provides a heat recovery apparatus comprising in flow series, an incinerator, a first heat ecxhange apparatus and a fluidised bed heat exchange apparatus, the fluidised bed heat exchanger including fluid bed material; a counterflow heat exchanger and a fluidising fan, the incinerator receiving hot contaminated gases from process equipment and discharging heated gases to the fluid bed material via the first heat exchange apparatus, a fluid to be heated passing through the heat exchanger located in the fluidised bed.

A recuperator may be located in the exhaust from the fluidised bed in order to pre-heat the fluid passing to the heat exchanger located in the fluidised bed.

The waste gases to be burned in the incinerator may comprise the discharge from textile processing apparatus, such as a stenter.

The first heat exchange apparatus can comprise a waste heat boiler, or an air to air heat exchanger.

The heat exchanger in the fluidised bed heat exchange apparatus is preferably of the counterflow type in which the fluid eg water, to be heated follows a circuitous path backwards and forwards across the direction of flow of heated gas through the fluid bed.

The present invention further resides in the provision of a counterflow heat exchanger in a fluidised bed heat exchange apparatus.

The present invention will now be more particularly described with reference to the accompanying drawings in which: Figure 1 shows a diagramatic layout of one form of heat recovery apparatus according to the present invention, Figure 2 shows a further form of heat recovery apparatus according to the present invention, Figure 3 shows one form of heat exchanger for use with the heat recovery apparatus illustrated in Figures 1 and 2, and Fig. 4 shows a diagramatic layout of another form of heat recovery apparatus according to the present invention.

Referring to Figure 1 a heat recovery apparatus (10) is arranged to receive the discharge and waste gases from a stenter (12).

The heat recovery apparatus comprises in flow series, an incinerator (14), a waste heat boiler (16), and a fluidised bed heat exchange apparatus (18).

The discharge waste gases usually comprising air at approximately 17500 and containing contaminants, is burned in the incinerator (14) using a gas burner. The temperature of the exhaust air is elevated to approximately 7500C and this heated air is used in the waste heat boiler (16) to make steam and/or condensate. The heated air which is now cooled to approximately 2600C is then passed to the apparatus (18) in which is located a heat exchanger (20). The heat exchanger receives water to be heated from a recuperator (22) and discharges the water heated to approximately 95"C. The fluidising air is drawn through the bed by a fan (24) and the air which has now been cooled to approximately 800C is discharged to atmosphere via the recuperator substantially free of contaminants.

It will be appreciated that a heat recovery apparatus as described with reference to Figure 1 enables contaminated, relatively hot air to be cleansed and also enables heat to be recovered in the form of steam and/or condensate and relatively hot water. An air to air heat exchanger can be used instead of the waste heat boiler so that heat can be recovered in the form of relatively hot air as will be described below with reference to Fig. 4.

Referring to Figure 2 which shows a heat recovery apparatus according to the present invention in more detail, there is shown an incinerator (26) having a gas burner (28). The apparatus has two intakes (28,30) both provided with filters, the inlet (28) enabling gases for example exhaust air from a stenter to be burned in the incinerator (26) and the inlet (30) enabling waste heat gases from an industrial process source to enter the apparatus directly.

The discharge from the incinerator (26), or from the intake (28) flows to a fluidised bed heat exchange apparatus (32) which comprises a casing (34) and distribution pipes (36) to distribute the discharge from the incinerator or the inlet (30) evenly throughout the bed. The fluid bed material comprises silica sand which is suitable for high temperature operation and tends not to degrade into "fines". The fluidised bed has sufficient freeboard to prevent any substantial quantity of fluid bed material flowing out of the casing (34) and a filter (38) is provided to remove any of the fluid bed material from the air discharged to atmosphere. The fluidised bed includes a counter flow heat exchanger (40) illustrated in more detail in Figure 3.

The output of air from the fluidised bed is discharged through a recuperator (42), by a fan (44) and then discharged in a cooled state to atmosphere. The air is also drawn through the fluidised bed by the fan (44). The air should be discharged to atmosphere at about 800C, otherwise if this temperature is lower, the low point will be reached, resulting in undesirable condensation.

The recuperator has a cold water inlet (46) and an outlet (48), the outlet (48) being connected to the input (50) to the heat exchanger (40) in the fluidised bed.

In use relatively hot contaminated waste gases are supplied to the incinerator (26) via the inlet (28) where the temperature of the waste gases is raised to a sufficient level and for a sufficient period of time to remove undesirable contaminants, particularly to meet any prevailing environmental regulations. The heated waste gases are passed through the distribution pipes (36) of the fluidised bed under the suction effect of the fan (44) in order to fluidise the bed material and cold water is passed through the inlet (46) of the recuperator (42) so as to preheat the supply of water to the heat exchanger (40) in the fluidised bed.There is a high rate of heat exchange between the fluidising air in the fluidising bed and the water flowing through the heat exchanger in the fluidised bed and the cooled air flows from the fluidised bed through the filter (38) and out through the recuperator (42) drawn by the fluidising fan (44).

It will be appreciated that the output from the heat exchanger in the fluidised bed can either be high temperature hot water or steam, depending upon the input temperature of the fluidising air and the rate of heat exchange. Also it will be appreciated that heat recovery apparatus as shown and described with reference to Figure 2 provides a means of removing contaminants from waste gases and also saving energy by recovering a substantial proportion of the heat in these waste gases.

Referring to Figure 3 the counter flow heat exchanger (40) in the fluidised bed comprises a number of separate elements, each of which is connected to an inlet manifold (54) and an outlet manifold (56). In each element a circuitous path is defined by seams (58) so that the water flows in a counterflow direction as illustrated by the arrows A. The direction of flow of waste gases through the apparatus (18) is in the direction of arrows B. It will be appreciated that the flow of water being heated is backwards and forwards across the flow of waste gases, and in a descending direction through a rising temperature gradient in the fluidised bed. The temperature in the fluidised bed decreases from the lower to the upper part of the bed.Therefore the water to be heated flows through the heat exchanger (40) against a rising temperature gradient, and it has been found that the combination of a circuitous flow path and rising temperature gradient results in an improved heat exchange efficiency.

An air to air heat exchanger can be provided externally of the fluidised bed so as to provide hot air instead of or as well as either hot water or steam, as shown in Fig. 4.

Referring to Fig. 4, instead of a waste heat boiler located in line between an incinerator and a fluidised bed heat exchange apparatus, an air to air heat exchanger (60) is provided. The heat exchanger (60) receives the incinerated stenter waste gases through an inlet (62) and air to be heated is drawn in from atmosphere by a fan (64) through an inlet (66). The heated air is discharged from an outlet (68) back to the stenter (12), whilst the incinerated waste gases pass through an outlet (70) into a fluidised bed heat exchange apparatus (18). The apparatus (18) is of the same type as has been described with reference to the previous Figs.

The heat exchanger (60) has a bypass (72) connecting the inlet (62) and the outlet (70), and is provided with a valve (74). The bypass and associated valve provide a means of controlling the rate of heat exchange in the heat exchanger (60)

Claims

CLAIMS 1. A heat recovery apparatus comprising in flow series an incinerator, a first heat exchange apparatus and a fluidised bed heat exchange apparatus, the fluidised bed heat exchange apparatus including fluid bed material, a counter flow heat exchanger and a fluidising fan, the incinerator receiving hot contaminated gases from processing equipment and discharging heated gases to the fluid bed material via the first heat exchange apparatus, a fluid to be heated passing through the heat exchanger located in the fluidised bed heat exchange apparatus, the cooled waste gases being exhausted to atmosphere.
A heat recovery apparatus as claimed in claim 1 in which the apparatus includes a recuperator arranged to receive the gases discharged from the fluidised bed and to discharge those cooled gases to atmosphere and to receive a fluid to be heated and to discharge heated fluid to the heat exchanger in the fluidised bed heat exchange apparatus.
3. A heat recovery apparatus as claimed in claim 1 or claim 2 in which the heat exchanger in the fluidised bed heat exchange apparatus comprises a counterflow heat exchanger in which the fluid to be heated flows through the counterflow heat exchanger backwards and forwards across the flow of gases through the fluidised bed.
4. A heat recovery apparatus as claimed in claim 3 in which the intake of fluid to be heated in the counterflow heat exchanger enters the heat exchanger at the upper end of the fluid bed and is discharged from the heat exchanger at the lower end of the fluid bed.
5. A heat recovery apparatus as claimed in claim any one of the preceeding claims in which the first heat exchange apparatus comprises a waste heat boiler arranged to receive water to be heated and to discharge either steam or steam and condensate and to receive hot waste gases from the incinerator and to discharge waste gases to the fluidised bed exchange apparatus.
6. Heat recovery apparatus as claimed in any one of the preceeding claims 1-4 in which the first heat exchange apparatus comprises an air to air heat exchanger arranged to receive air from atmosphere to be heated and to discharge heated air to industrial process equipment and to receive heated waste gases from the incinerator and to discharge waste gases to the fluidised bed heat exchange apparatus.
7. Heat recovery apparatus as claimed in claim 6 in which the air to air heat exchanger includes a bypass connecting the discharge from the incinerator to the inlet to the fluidised bed heat exchange apparatus, the bypass including valve means to control the flow of gases through the bypass.
8. Heat recovery apparatus as claimed in any one of the preceeding claims in which the input to the incinerator comprises discharge waste gases from an industrial process.
9. Heat recovery apparatus as claimed in claim 8 in which the industrial process apparatus comprises a stenter.
10. Heat recovery apparatus as claimed in any one of the preceeding claims in which the fluidised bed heat exchange apparatus includes an inlet arranged to receive waste gases from in industrial process directly.
11. Heat recovery apparatus constructed and arranged for use in operations substantially as herein described and with reference to the accompanying drawings.