US3516370A - Furnaces - Google Patents

Description

June 23, 1970 J. B. STRIBLING FURNACES 5 Sheets-Sheet 1 Filed April 18, 1968 m/QMTOQ:

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FURNGES Filed April 18, 1968 5 Sheds-Sheet 5 lux/mu@ TOHM /lmd STRlBLMlG bq k \U ACK/MT United States Patent O 3,516,370 F URNACES John Brian Stribling, Sutton Coldfield, England, assignor to Caval Developments Limited, Wedneshury, England,

a British company Filed Apr. 18, 1968, Ser. No. 722,324 Int. Cl. F23g 7/00 U.S. Cl. 110-7 1 Claim ABSTRACT F THE DISCLOSURE The invention provides a furnace for burning waste material and arranged to be fed from two separate sources with different kinds of material.

This invention relates to furnaces.

Considerable difculty is often experienced in the disposal of finely divided particulate of materials, such as wood waste, since such materials cannot readily be disposed of by tipping or otherwise dumping on open ground, and the alternative of burning is unsatisfactory in that the material either will not burn readily in conventional boilers and furnaces, resulting in incomplete combustion and subsequent atmospheric pollution, or alternatively may be explosive when mixed with air in the correct proportions so that combustion is a hazardous operation.

It is an object of the present invention to provide a furnace for burning finely divided particulate materials which gives an efciency of combustion greater than that of conventional types of boiler or furnace, which minimizes the explosion hazard, and which also enables other types of material to be burnt.

According to the present invention a furnace comprises a first generally cylindrical combustion zone having an inlet for combustible material arranged tangentially at its periphery and a further combustion zone communicating with the said rst zone and having a separate inlet, and furnace temperature responsive ow control means whereby the rate of flow of material to said first zone may be controlled in accordance with a predetermined furnace temperature range. The two combustion zones may be more or less coextensive within the furnace.

Preferably the inlet to said second zone is in the form of a refractory lined sloping chute and is normally closed by a furnace door. Advantageously the door is disposed in a compartment which is adapted to be pressurized in those instances where the furnace itself is operated at a positive pressure.4

Various embodiments of the invention are now more particularly described with reference to the accompanying drawings wherein:

FIG. 1 is an elevation of one embodiment and FIG. 2 is a plan thereof,

PIG. 3 is an elevation of a second embodiment and FIG. 4 is a plan thereof, and

FIG. 5 is an elevation of a third embodiment.

Referring now to FIGS. l and 2, the furnace comprises a vertical generally cylindrical chamber having an inlet 11 for tine combustible material arranged tangentially at its periphery near the top of the chamber.

Combustible material in finely divided form may be fed via the tangential inlet together with combustion air from fan 12 at a high velocity so that a spiral ow pattern within the chamber extends downwardly from the inlet. When the combustible material/ air mixture is ignited the flame pattern also conforms with the spiral flow and the products of combustion are therefore generated at a position below the inlet in the zone 15.

The combustion chamber 10 is located in a pit 32 so as to be partly below ground level, so that the feed pipe ice extending between the fan 12 and inlet 11 extends substantially at ground level.

The products of combustion escape from the chamber via the central vortex, defined by the flow pattern, and a stack 16 is disposed above the cylindrical combustion chamber to vent them to atmosphere. By virtue of the fact that the products of combustion are compelled to traverse a region of extremely high temperature the effluent from the stack contains very little, if any, unburnt material.

The lower end of said cylindrical combustion chamber is provided with a sloping side chute 21 whereby solid particles of combustible material too large or too heavy for admission through the tangential inlet 11 may be admitted by periodic manual operation. This chute is closed with a furnace door 20 horizontally located at the top of the chute and contained within a compartment 21a which is adapted to be maintained at pressure greater than that in the body of the furnace by means of a high pressure fan and motor 39. Access to the compartment 21a is given through a further door 38, the closing of which door controls the pressurizing of the compartment. In addition, to prevent undesirable abnormal build up of pressure in the furnace, which by communicating with the compartment 21a through the side chute 21 might lift door 20 and burst open door 38 to the subsequent harm of the operator, a further top outlet to the compartment 21a is closed by a pressure sensitive bursting panel 33 contained in an extension duct 22 to guide such outbursting gases away from the zone of the operator.

Whilst these features prevent danger from burning material in the area of the furnace operator it is also desirable to provide means of preventing excessive pressures of combustion gas from passing back from the furnace 10 through the inlet 11 and possibly causing damage elsewhere. Such means comprises a pneumatic gate which serves as a control valve, being located between the inlet 11 and the position of entry of fine dust from the storage hopper 27 which is generally in a position adjacent to the fan 12 providing combustion air and conveying air for the material. The gate 40 is operable automatically by a pneumatic or electrical failure in the pneumatic feed system, or by a sudden change in pressure in that system which might be caused by abnormal rise in pressure in the furnace chamber preceding a blowback of hot gas through the inlet 11. Thus the gate may be controlled by a device which responds to the current being used by the fan, and in addition a device which responds to the velocity of the combustible material/ air mixture in the inlet duct, and in addition a device which responds to changes in the pressure of the air mixture in the inlet duct. The pneumatic gate prevents the back ignition of dust into the pneumatic feed due to the flame travel rate exceeding the rate of flow of the combustible material/air mixture. Additionally, a restrictive orifice device at the inlet 11 normally maintains the speed of the combustible material/ air mixture at a rate above that of the normally expected speed of back propagation of flame, and additionally again, means are provided by a rotary metering and sealing valve 26 to prevent any such back propagation of llame as may conceivably escape both the restrictive device 11 and the pneumatic gate 40 from communicating with the wood waste stored in the main hopper storage system 27. Additionally again, a duct extension is fitted to the inlet of fan 12 whereby `means are taken to ensure that any flame passing through all the above mentioned points in the system is deflected to atmosphere at a point where no danger either to the operator or to the equipment can occur.

Flow of combustible material to the tangential inlet 11 is effected by means of the fan 12 arranged on the inlet side of the chamber so that the furnace operates at a positive pressure. The feed of material is effected through a rotary metering valve 26 from a main storage hopper 27 by means of a mechanical arch breaking and rotatory discharging device 26a, both this device and the rotary metering valve 26 being capable of adjustment in speed to give variation of rate of feed of combustible material either manually or automatically according to furnace temperature (sensed by probe 26b and operatively coupled to said valve 26) as indicated by the dash- 1ine26c.

The main storage hopper 27 would normally be filled by means extraneous to the system presently described, such as a pneumatic extraction system from the machines forming the waste, having a main cyclone discharge unit mounted immediately above the said hopper. The arrangement is particularly suitable for use to burn waste from joinery work and the like, and wood dust from e.g. sanding machines which may be fed through pipe 30 to the cyclone for separation therein of the entraining In operation, when fine combustible material is to be burnt from the storage hopper 27, the furnace door 20 is closed and the pressure compartment door 38 is also closed. A fire having previously been lighted in the furnace chamber wood dust from the storage hopper 27 would be fed automatically by means of the discharge equipment 26a through the rotary metering valve 26 into the pneumatic line powered by fan 12. When larger material was to be added manually, the control valve 40 `would be closed, which closure would automatically stop feed of material through valve 2,6, and would additionally by operation of an electrical lock enable the furnace door to be raised and the pressure compartment door 38 to be opened. The furnace would then no longer be under positive pressure and material could safely be admitted manually. Means are provided by limit switches and electrical interlocks to prevent accidental opening of the furnace door while the furnace is under positive pressure, and alternatively to prevent the pressurising of the furnace by opening valve if the furnace door 20 is already open.

One or more thermocouples (not shown) are mounted within the furnace chamber and arranged so as to operate the rotary metering valve 26 and discharger 26a and thereby control the admission of particulate combustible material to the furnace. In particular this control would prevent admission of any particulate material unless the furnace temperature was sufficiently high to prevent delayed ignition of dust with attendant risk of explosion, and alternatively would prevent feed of particulate material if the furnace temperature was already at a maximum, such minimum and maximum temperatures being by way of example 600 C. and 1000 C. Additionally the feed devices 26 and 26a which are preferably or possibly manually adjustable can also be arranged with mechanical and electrical control to vary the rate of feed according to the conditions existing in the furnace at that time.

By virtue of this control it is impossible for a build up of combustible material to occur within the combustion chamber and therefore the possibility of an explosion occuring is minimized.

It will be seen that the furnace can be used for combustion of manually fed waste through side chute 21 wherein the temperature is not Within the required range for the particulate waste feed to be brought into operation. When the temperature has been brought to the required minimum temperature however the feed of particulate waste will cut in and combustion thereof will take place concurrently with the combustion of the waste admitted manually through the side chute.

In addition to the temperature control it is desirable that the control of waste be effected in response to the presence of a flame in the furnace. This may be effected by the inclusion of a photoelectric device (not shown) which will control the feed of particulate waste to the furnace.

Depending upon the anticipated amount of waste for any particular installation a faciilty for burning an auxiliary fuel may also be provided as in the case of the embodiment of FIGS. 3 and 4.

Referring now to FIGS. 3-4, this includes furnace 10 with inlet 11, chute 21 and other parts all identical to those in FIGS. 1-2 except that the chimney or flue 16 is connected to a waste-heat boiler so as to utilise the heat of the exhaust gases for water heating or steam raising. In this event then, an oil burner 52 is mounted to discharge combustion products into the exhaust gas passages on occasions when furnace 10 is not operating. Particularly in such cases, a suction fan 55 at the tail end of the boiler may be operated to induce flow through the boiler, although this also makes it possible to run fan 12 at lower operating speed and air ow rate or even in some cases dispense with fan 12. The used gas passage 57 communicates with fan 55 which communicates with cyclones 58 for grit and ash separation before discharge of combustion products into the final ue or chimney 60. If the boiler is used for space-heating purposes, water may be circulated via tlow and return pipes 62.

In the modification shown in the embodiment of FIG. 5, the furnace 10 has the inlet 11 and a simple access door for feeding large pieces, and this essentially uses the suction fan 55 as shown in FIGS. 3-4 so that the furnace is at negative pressure when operating. This may be desirable in cases where the supply of waste is not available continuously so that when the waste feed is exhausted the auxiliary fuel may be burned. This is particularly convenient when the furnace is coupled to heat exchange means as referred to or alternatively as a steam raising boiler where it is desired that the production of steam should not be dependent upon the production of waste material.

In addition to the temperature control it is desirable that further controls be included in order to minimise the possibility of explosion. Electrical interlocks may be provided to prevent the opening of the furnace 10 door whilst the furnace is under a positive pressure or whilst the auxiliary fuel burner is in operation. Similarly the interlock may be arranged such that the pressurising of the furnace or the ignition of the auxiliary fuel burner is prevented whilst the door is open whereby the possi-bility of blow-backs is minimised.

One further contingency which is guarded against in all embodiments is the possibility that the ratio of combustible material/air in the feed will be excessive whereby the com-bustion of the material will not be complete. As a result of this, unburned material may escape from the stack or there may be a build up thereof with the resulting danger of explosion. Velocity and pressure switches (not shown) are, therefore, provided to control the admission of combustible material in relation to the quantity of air being fed.

Conversely an excess of combustion air is undesirable in that it reduces the eciency of the Vfurnace when the heat produced thereby is to be utilised. In order to regulate the air flow a control such as an iris diaphragm may be included (in all embodiments) in the inlet duct. If desired, two inlet ducts may be provided in each embodiment, one duct having an air flow control.

It will be appreciated that the furnaces of this invention provide an extremely convenient way of disposing of finely divided particulate materials such as wood waste. The waste, for example from a sanding machine, can be drawn into the system from a position immediately adjacent the machine and fed to the furnace via a pneumatic conveyor possibly via a fuel storage arrangement. By this means the escape of wood dust into the atmosphere is considerably reduced and, furthermore, the

disposal of the dust is effected in a neat, simple and economic manner.

I claim:

1. A furnace comprising a rst generally cylindrical combustion zone having an inlet for combustible material arranged tangentially at its periphery, said tangential inlet being connected to a pneumatic feed pipe for supplying combustible material and said feed pipe being connected to a fan for supplying combustion air so as to set up a spiral ow pattern in said zone and ensure complete combustion in said Zone, and a further combustion zone communicating with said rst zione but located on the opposite side of said rst zone to an outlet therefrom so that material burnt in said further zone -must pass through the rst said zone before reaching said outlet, said further zone having aseparate material inlet, and flow control means responsive to furnace temperature whereby the rate of flow of material into said first zone may be controlled in accordance with a predetermined furnace temperature range.

References Cited UNITED STATES PATENTS 1,893,913 l/l933 Saint-Jacques 110-28 X 2,925,055 2/1960 Miller et al. 11G-105 l0 3,218,997 11/1965 Berghout et al. 11G- 18 EDWARD G. FAVORS, Primary Examiner U.S. Cl. X.R.

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