GB2357138A

GB2357138A - An air heating system for a furnace

Info

Publication number: GB2357138A
Application number: GB0024508A
Authority: GB
Inventors: Clive Hall
Original assignee: THERMAL TECH CONSULTANCY Ltd
Current assignee: THERMAL TECH CONSULTANCY Ltd
Priority date: 1999-10-21
Filing date: 2000-10-06
Publication date: 2001-06-13
Also published as: GB9924811D0; GB0024508D0

Abstract

A furnace (2), for burning waste cut-offs of wood, cardboard, paper and the like is provided with an oil or gas fired after burner (26) for re-combustion of spent gasses from a combustion chamber (4) in order to ensure that emission standards for the flue gasses are met. The furnace comprises a fan (30) connected to ducting which partially surrounds the combustion chamber, which ducting, when the furnace is in use, facilitates the delivery of air to be heated to an upstream end of a heat exchanger (10) at a temperature T1. Thereafter, re-combustion gasses from the after burner pass through the heat exchanger to heat the air from a temperature T1 to a temperature T2. The heated air may be utilised for heating a work area of a factory.

Description

2357138 IMPROVEMENTS IN A HEATING SYSTEM AND A FURNACE This invention is

concerned with improvements in or relating to a heating system and a furnace for use in a heating system.

Furnaces and heating systems incorporating furnaces are designed to be efficient in their use of fuel; however, at this time, when government directives and environmental requirements dictate the criteria for meeting emission targets for spent flue gases and the disposal of waste, it is more and more the responsibility of the manufacturers of new furnaces and heating systems incorporating such furnaces to ensure that their products are environmentally friendly.

In overcoming the problems of disposing of waste off-cuts of wood, cardboard, paper and the like material together with the ever present requirement to cut down on the emission of harmful flue gases from furnaces, the applicant has devised a novel heating system incorporating a novel furnace typically, but not exclusively, of 0.4 to 3MW rating for burning wood, cardboard or paper waste at up to 625 kg/hr.

Thus, the invention conveniently provides a heating system comprising:

a) fluid delivery means for a fluid to be heated; b) a combustion chamber; c) a heat exchanger; d) a flue for exhausting spent gases; e) a re-combustion means in the form of an after-burner, provided between the combustion chamber and the heat exchanger, for re-combusting the spent gases from the combustion chamber, characterised in that the fluid delivery means comprises a fan connected to ducting adjacent to peripheral walls of the combustion chamber, a downstream end of the ducting being connected to an upstream end of the heat exchanger, for effecting, when the heating system is in use, the delivery of fluid to be heated through the ducting to the upstream side of the heat exchanger at a temperature T1.

2 Conveniently, when the system is in use, the after burner re-combusts spent gases from the combustion chamber prior to the gases being directed through the heat exchanger to the flue, the re-combusted gases being effective to raise the temperature of the fluid passing through the heat exchanger from a temperature T1 to a temperature T2.

The fluid heated by the system is conveniently ducted to warm air blowers and/or radiators and/or hot water boilers.

Preferably, the fluid to be heated is ambient air and the after burner is preferably an oil or gas burner.

The present invention also conveniently provides a furnace comprising:

a) a combustion chamber; and, b) a flue for exhausting spent gases; c) a re-combustion chamber in the form of an after burner provided between the combustion chamber and the flue; d) a heat exchanger downstream of the re-combustion chamber; characterised in that the furnace comprises delivery means for a fluid whereby, when the furnace is in use, the fluid is heated by the combustion chamber to a temperature T1 and by the heat exchanger to a higher temperature T2.

Conveniently, the present invention also provides a method of reducing harmful emissions of flue gases from a furnace, according to the last preceding paragraph, by passing the spent gases from a combustion chamber of the furnace through an after burner downstream of the combustion chamber but upstream of a flue for exhausting the spent gases from the furnace.

There now follows by way of example of the heating system and the furnace provided by the invention a detailed description, which is to be read with reference to the accompanying drawings in which:

Figure 1 is a front elevation of the furnace provided by the invention; and, Figure 2 is a section view along the line 11-11 of Figure 1.

3 In order to provide an efficient and environmentally friendly heating system and furnace, the invention provides a furnace 2 which generally comprises a combustion chamber 4, a delivery means 6 for ambient air to be heated in the furnace, an after burner 8 located downstream of the combustion chamber 4, a heat exchanger 10 downstream of the after burner 8, ducting 12 for air heated in the furnace and a flue 14 for exhausting the spent gases from the furnace 2, see Figures 1 and 2.

Specifically, the combustion chamber 4 is of conventional design and is provided with an access door 16 incorporating an air regulating port 18 through which access door 16 combustible material is loaded manually or by an automatic feed device, not shown, into the combustion chamber 4.

The chamber 4 is connected by a chimney 20 at its rearmost end 22 to a combustion chamber 24 of the after burner 8.

The after burner 8 also comprises an oil or gas burner 26 operation of which, when the furnace 2 is in use, is controlled by means not shown to re-combust the spent gases from the combustion chamber 4.

The combustion chamber 24 is provided with an access door 28 for inspection purposes, see Figure 2.

The air delivery means 6 is provided by a fan 30 connected to ducting 32 and 34 formed in the peripheral side walls 36 and 38 respectively of the combustion chamber 4, see Figure 1.

At a downstream end thereof, the ducting 32 and 34 is connected to an upstream side 35 of the heat exchanger 10, the ducting 12 being connected to a downstream side of the heat exchanger 10 to receive and dissipate,when the furnace 2 is in use, the ambient air fed by the delivery means 6 and heated in the heat exchanger 10 of the furnace 2.

The heat exchanger 10 is also of conventional design and is provided with sixteen heat exchanger tubes 42 extending between a wall 44 of the after burner combustion chamber 24 and a wall 46 of the flue 14, see especially Figure 2. The wall 44 also includes a refractory baffle 48 for the protection of the tubes 42 when the furnace is in use.

When the furnace 2 is in use for the purposes of; a) combusting waste with the emission of harmful gases reduced to a minimum commensurate with complying with government directives andlor environmental 4 requirements, and b) complying with such regulations relating to recycling of waste, the combustion chamber 4 is loaded with off-cuts of wood, cardboard, waste paper and the like materials and ignited.

Spent gases from the combustion chamber 4 pass through the chimney 20 to the combustion chamber 24 of the after burner 8 where they are re-combusted to reduce the amount of harmful gases exhausted to the flue 14 through the tubes 42 of the heat exchanger 10, see Figure 2.

At the same time ambient air and/or preheated air, or a mixture thereof, is fed by the fan 30 through the ducting 32 and 34, where it is heated to a temperature T1 by the heat from the combustion chamber 4, the air passing through the ducting 32 and 34 to the downstream side 35 of the heat exchanger 10.

Thereafter, the air heated to a temperature TI is fed over and around the tubes 42 of the heat exchanger 10 where it is heated to a higher temperature T2 by the heat from the after burner gases which are passing through the tubes 42 of the heat exchanger 10.

The heated air may be utilised for many purposes, for example, it can be directed by the ducting 12 to hot air radiators for heating a work area of a factory, to hot water boilers and steam generators and the like.

It will be readily appreciated that there is a significant reduction in the harmful emissions from a furnace incorporating the after burner as taught by the present invention.

The combustion chamber 4 has been specifically designed for burning waste wood, cardboard, chipboard, wood chips,sawdust and certain carbonaceous skip debris not including PVC or any toxic waste materials.

The after burner 8 is designed to operate at temperatures of 800 to 1000 degrees centigrade, the temperature being controlled by a high/low oil or gas burner from a 2-set point temperature controller with a thermocouple within the after burner 8. These conditions facilitate the reduction of particulate levels below the 50 mg/m3 as set by the Environmental Protection Act for wood burning processes.

It will be evident that, in addition to the temperature requirement for the after burner, it is also necessary to ensure that the dwell-time, of the spent gases from the combustion chamber 4, in the combustion chamber 24 is sufficient for purpose. Also the supply of oxygen to the combustion chamber 24 must be sufficient to achieve the desired result.

6

Claims

1. A heating system comprising:

2. A heating system according to Claim 1 characterised in that, when the system is in use, the after burner re-combusts spent gases from the combustion chamber prior to the gases being directed through the heat exchanger to the flue, the re-combusted gases being effective to raise the temperature of the fluid passing through the heat exchanger from a temperature T1 to a temperature T2.

3. A heating system according to either one of Claims 1 and 2 characterised in that fluid heated by the system is ducted to warm air blowers and/or radiators and/or hot water boilers.

4. A heating system according to any one of the preceding Claims characterised in that the fluid to be heated is ambient air.

5. A heating system according to any one of the preceding Claims characterised in that the after burner is an oil or gas burner.

6. A furnace comprising:

a) a combustion chamber; and, b) a flue for exhausting spent gases; c) a re-combustion chamber in the form of an after-burner provided between the combustion chamber and the flue; 7 d) a heat exchanger downstream of the re-combustion chamber; characterised in that the furnace comprises delivery means for a fluid whereby, when the furnace is in use, the fluid is heated by the combustion chamber to a temperature T1 and by the heat exchanger to a higher temperature T2.

7. A method of reducing harmful emissions of flue gases from a furnace according to Claim 6 by passing the spent gases from a combustion chamber of the furnace through an after burner downstream of the combustion chamber but upstream of a flue for exhausting the spent gases from the furnace.