GB2071357A - A method and apparatus for controlling a solid fuel furnace - Google Patents

Abstract

A solid fuel furnace 6 has a fuel supply and discharge mechanism. Fuel supply means comprises a fuel supply fire grate 8 (Fig. 5) to supply fuel to the furnace 6. The discharge mechanism comprises an ash discharge fire grate 10. The ash discharge fire grate 10 is oscillated to remove clinker and ash from the furnace 6 into an ash chamber 15. The fuel supply and discharge mechanism is responsive to a signal indicative of room temperature, and thereby the combustion in the furnace is controlled. To prevent discharge of unburnt fuel, this signal is ignored if it arises within less than a minimum time T1 after an operation of the fuel supply and discharge mechanism. The mechanism is operated after a maximum time T2, corresponding to exhaustion of fuel, even if the said signal is not present, thus preventing the furnace from going out. <IMAGE>

Description

SPECIFICATION A method and apparatus for controlling a solid fuel furnace This invention relates to a method and apparatus for controlling a solid fuel furnace.

Conventionally, in this type of furnace, for example, a small coal-burning boiler, only the water temperature in the boiler is detected with a temperature sensor, and operations such as operating the fire grate are manually conducted by measuring the temperature with a thermometer or sensing it with the skin. To maintain the desired heat, personal vigilance is required. Because of difficulties in knowing the appropriate combustion conditions, such problems occur in that unburnt fuel is discharged if the timing of the operation in the fire grate is too early or if the grate its operated too often to meet a rapid change in a room temperature as at the time of opening and shutting of a room door or window, or if the timing is too late, the combustion is extinguished.

It is an object of this invention to provide a method and apparatus for controlling a solid fuel furnace, which ensures stable combustion, while avoiding personal vigilance and labour necessary for the operation of the fire grate and preventing a discharge of unburnt fuel and extinguishing of the combustion source.

It has been found that time elements T1 and T2 are important factors to solve these problems. T, is defined as the time during which a fire force can be maintained without a reduction after the completion of one operation of the fuel supply and discharge mechanism and T2 is defined as the time during which the combustion can continue after the completion of one operation of the fuel supply and discharge mechanism.

This invention is a method of controlling the combustion in a solid fuel furnace having a fuel supply and discharge mechanism comprising a fuel supply means to supply the fuel to the furnace and an ash discharge means to remove ash from the furnace, in which the fuel supply and discharge mechanism is operated to control the combustion in the furnace.

This invention is also a method of and apparatus for controlling a solid fuel furnace characterised in that the fuel supply and discharge mechanism is not operated during the time T1 counted from the start of the operation of the fuel and discharge mechanism without accepting the operation signal if received, the fuel supply and discharge mechanism being operated in a predetermined pattern of movements when the operation signal is received after the lapse of the time T1, and the fuel supply and discharge mechanism being operated even in the absence of the operation signal after the lapse of the time T2.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a plan view of a boiler according to the invention; Figure 2 shows a vertical section of the boiler shown in Figure 1; Figure 3 shows a section of the boiler taken along Ill-Ill in Figure 2; Figure 4 shows a vertical section of the boiler taken along IV--IV in Figure 2; Figure 5 shows a section of the furnace used in the boiler of Figure 2; Figure 6 shows a partly broken away, plan view of the fuel supply and discharge mechanism; Figure 7A is a flow sheet (the left-hand portion) of means for automatic control according to the invention; Figure 7B is a flow sheet (the right-hand portion) of means for automatic control according to the invention; and Figure 8 is a diagram of operation signals used in the means for automatic control.

Figures 1 to 6 show an embodiment of the invention with a small coal burning boiler. An outer case 1 has within it a cylindrical water tank 2, the outside of which is almost wholly surrounded by a smoke flue 3. An upper part of the inside of the water tank 2 forms a coal storage chamber 4, which is designed to store about 60 kg (two to three days supply) of powdered coal (including lumps). The coal includes primarily smokeless coal. The lower end of the coal storage chamber 4 has a hopper 5 leading to a furnace 6.

The furnace 6 has a fuel supply fire grate 8 as a fuel supply means, a clinker breaking fire grate 9 and an ash discharge fire grate 10 as an ash discharging means, all rotatably supported on a beam 7.

Figure 2 also shows a heat-resisting liner 11 made of such material as heat-resisting cast iron.

The furnace 6 is connected to the smoke flue 3 through a communicating hole 12 (Figure 4).

Inspection windows 13 and 4 permit inspection of the interior of the furnace 6.

Below the lower end of the furnace 6, there is an ash chamber 1 5 which receives cinders.

Under the lower portion of the smoke flue 3, there is a secondary air duct 16, which is linked with the smoke flue 3 through an air conduit hole 17.

A motor 18 drives a fan 19 for circulating a secondary flow of air to the secondary air duct 1 6 and a fan 20 for blasting a primary flow of air to the furnace 6 from its lower portion through the ash chamber 1 5.

Figures 2 and 4 show a coal supply opening 21, a gas discharge opening 22, a water supply opening 23 and a heated water outlet opening 24.

The temperature of the heated water in the water tank 2 is measured by a thermometer 25 in the outer wall of the water tank 2. The temperature of the discharge gas inside the smoke flue 3 is measured by a thermometer 26 in the outer wall of the smoke flue 3.

The structure around the furnace 6 will now be explained in detail with reference to Figures 5 and 6.

The ash discharge fire gate 10 rotatably mounted on a projecting shaft 32 of the beam 7 has a pin 27 projecting from its lower surface, which is connected by a joint rod 31 to a pin 30 on a rotary disc 29 of the driving means 28. As the disc 29 rotates, the driving means 28 oscillates the ash discharge fire grate.

An arm 33 rotatably mounted on the projecting shaft 32 and its boss 34 serves as a jaw clutch to engage with a boss of the clinker breaking fire grate 9. At an end of the arm 33, a pin 35 is connected by a joint rod 39 to a pin 38 on a rotary disc 37 of a driving means 36 located outside the furnace 6. The driving means 36 drives the clinker breaking fire grate 9 and the fuel supply fire grate 8. The fuel supply fire grate 8 is fixed to and rotates jointly with the clinker breaking fire grate 9. Therefore, when the disc 37 rotates, both the clinker breaking fire grate 9 and the fuel supply fire grate 8 are oscillated.

When the ash discharge fire grate 10 is oscillated, ash accumulated thereon drops into the ash chamber 1 5 through.gaps 40. When the fuel supply fire grate 8 and the clinker breaking fire grate 9 are oscillated, part of the coal in the coal storage chamber 4 drops through the supply hopper 5 and the clinker produced during the combustion is broken up to pass through the gaps 40 at the same time.

Since the relationship between the amount of a coal supply and ash discharge and oscillating reciprocative movements of the fuel supply fire grate 8, the clinker breaking fire grate 9, the ash discharge fire grate 10, the driving means 28 and 36 and other parts connecting them varies, depending on kinds and characteristics of coal, it is desirable to find out through prior experiments the most appropriate amounts of movement of each part, an oscillating speed, a time gap and an oscillating angle. In the case of this embodiment of the invention, this can not be changed, but, if a cylinder is employed, it can be changed by adjusting its stroke. This is in accordance with the desired amount of supply and discharge and other factors such as kinds and characteristics of coal and input their movement patterns into the memory means.

An embodiment of this invention for automatic operation of a small boiler with a structure as mentioned above is shown in Figures 7A and 7B.

Figure7A is a flow sheet which shows the start of the automatic operation as a push button or a touch switch 41. A decision 42 is implemented by the thermometer 25 measuring a water temperature in the water tank 2 and serving as a safety sensor and involves a safety circuit, which judges a temperature exceeding 950C as dangerous and leads to the stop routine.

The lighting operation 43 can be done manually because this requires little labour. This is necessary only once at the start of its operation (lit once at the beginning of winter in the case of a stove), if the automatic operation is ensured perfectly. A decision 44 involves a circuit to confirm the lighting and is designed to be implemented by the thermometer 26 for a discharge gas temperature. The thermometer 26 is not required to be highly sensitive and it is possible to use a bimetallic thermometer with a sensing range from 500C to 1000C. The operation 45 is included as a reference in the case of a stove and is not required for a boiler.

In the decisions 46 and 47, GM, is an oscillation of the ash discharge fire grate 10 and GM2 is an oscillation of the fuel supply fire grate 8 and the clinker breaking fire grate 9. A cycle of oscillations is the pre-determined number of oscillating reciprocations of GM, and GM2.

The decision 48 involves a circuit to conduct its decision by the thermometer 25 and checks whether a temperature reaches a pre-set level (200C to ....... continuously adjusted by an operation panel or 200C, 400C, 600C and 800C by a digital, for instance). If the level is satisfactory, the decision maintains the slow operation of the secondary fans 1 9 and 20, and, if not, the decision strengthens the operation of the fans 1 9 and 20 to raise a fire force.

The operation 49 involves a counter to measure time, starting almost immediately after GM, and GM2 are implemented by the decision 46 and the operation 47. A circuit starts counting the time if it has not started and continues to count if it has already started. In this embodiment of the invention, the time T1 is set at 1 5 minutes and the time T2 at 30 minutes, and the 30 minutes for the operation 49 corresponds to the time T2.

The decision 50 involves a circuit to determine whether the 1 5 minutes corresponding to the time T, has passed. If the 1 5 minutes does not pass, the decision prevents a progress to the next process and returns to the return point 51, ensuring the safety check by the decision 42, the confirmation of the lighting by the decision 44, the confirmation of the operation of the fuel supply and discharge mechanism by the decision 46, a check by the decision 48 of the amount of air for the combustion and a check by the decision 50 of passage of the time T, and repeating these checks and confirmations until the 1 5 minutes passes. If any abnormality occurs in this process, countermeasures are automatically taken as described hereinafter.For instance, if the water temperature exceeds 950C i.e. to a dangerous level, the operation is stopped as instructed by the decision 42, the re-lighting is done after the counting is cleared by the decision 44. If the movements of GM, and GM2 are not implemented despite the start of the counting, a cycle of their oscillations is effected by the decision 45. When the water temperature falls, the strength of the fans 1 9 and 20 for the combustion is raised to supply the most appropriate amount of air and to strengthen a fire force. With these and other counter-measures, the continuation of a stable combustion is ensured.

In this embodiment of the invention, if the thermometer 25 detects a drop in temperature of the water tank 2, e.g. when a water temperature is lower than a pre-set level (200C to 800 C), an operating signal instructing the operation of the fuel supply and discharge mechanism requiring an increase in the fuel supply. However, before the 1 5 minutes of the time T, passes, this signal only works to operate the secondary fans 1 9 and 20 at their most appropriate condition but the signal is not accepted as the operation signal for the fuel supply and discharge mechanism. Namely, the gate for the operation signal is closed until the 1 5 minutes of the time T, passes.

Since the fuel supply and discharge mechanism are not operated with the operation signal not accepted even if received when the water temperature temporarily falls below a pre-set level, it can prevent the unlit and unburnt fuel from being discharged and the still burning fuel from being made wasted as caused by too quick a reaction to a temporary temperature fall.

The passage of the 1 5 minutes leads to the next process, that is the decision 52. The decision 52 is implemented by the thermometer 25 for the water temperature in the water tank 2. A pre-set water temperature is the same as the decision 48 which is set at 200C to 800 C. Since the already mentioned confirmation operations are repeated before the decision 52, the combustion is supposed to be kept in the most appropriate state for the boiler. Therefore, the issue of the signal despite this is judged to indicate a shortage of fuel after the passage of the time T1, so that it is accepted as an operation signal to supply the fuel by actuating the fuel supply and discharge mechanism.

When a water temperature reaches a pre-set level and thus no operation signal is issued at the decision 52, the decision 53 is implemented. The decision 53 is to determine whether the 30 minutes corresponding to the time T2 from the start of the time counting has passed. If not, the decision 53 returns to the return point 51 without proceeding to the next process, effecting a process of the said confirmation operations. Thus, when a water temperature does not reach a preset level (no operation signal is issued) and the time does not pass 30 minutes, a process between the return point 51 and the decision 53 is repeated, effecting the above-mentioned checks, confirmations and counter-measures.

If the water temperature is judged at the decision 52 to be lower than a pre-set level during this process, it is accepted as an operation signal, leading to the next process. By the operation 55, the most appropriate operational pattern for the fire grate is selected in accordance with its operational conditions and kinds and characteristics of fuel (the operational pattern already selected manually with such a means as a push button is taken in or an operational pattern is automatically selected by finding out such factors as kinds and characteristics of fuel). GM, and GM2 are oscillated in the pre-determined number of reciprocations according to this operational pattern, supplying the pre-set amount of fuel and returning the process to the return point 56.

Namely, after the lapse of the 1 5 minutes of the time T1, the gate returns to the open position for the operation signal.

Then the process progresses and, upon reaching the operation 49, the time measuring means already cleared is re-set, resuming its counting. Accordingly, the time at the decision 50 is judged as not exceeding the 1 5 minutes and the said process is repeated from the return point 51.

When the operation signal (indicating the water temperature below a pre-set level) is not received while the gate is open after the 30 minutes of time T2 passes after the elapsed 1 5 minutes, the process is progressed by the operation 55 to actuate, as in the case of the operation signal being received, the operation 47 for the operation of the fuel supply and discharge mechanism through the operation 55 for the counting clear and operation pattern selection, thereby supplying the pre-set amount of fuel and preventing the combustion source from being extinguished.

As mentioned above, a sequence control can be employed but the use of microcomputer control enables a high performance with its system made compact.

Figure 8 is a diagram showing the operation of each part when an automatic control is implemented as mentioned above. An embodiment of the invention with a stove is shown in Figure 8. A room temperature signal (pulse) is employed as the operation signal, generated when a temperature of the indoor air or load which is being measured falls below a pre-set level.

Time lengths t, and t2 of the operation signals for GM, (an oscillation of the ash discharge fire grate 10) and GM2 (an oscillation of the supply fire grate 8 and the clinker breaking fire grate 9) are set to correspond with those of driving time of the driving means 28 and 36. But, in the case of the driving means being implemented by a solenoid, the signal can be given in the number of pulses corresponding to the pre-set number of reciprocations. Oscillations set by t1 and t2 constitute one cycle of operation of the fuel supply and discharge mechanism.

Each cycle ranges between the start of the GM, operation signal and the start of the next GM, operation signal. The gate is closed during the initial time T, of each cycle and opened after the lapse of the time T2. It remains open until it receives an earlier one of either the temperature signal pulse or the signal for the lapse of the time T2.

If the operation signal corresponding to the room temperature is not received in the first cycle until after the start, the gate remains closed until the time T, has lapsed and then open until being closed upon the lapse of the time T2, upon which the second cycle begins with the next GM, and GM2 operation implemented. In the second cycle, the room temperature signal is received and accepted in the time Ta set as T1, Ta, T2, actuating the next operation of GM, and GM2. The third cycle, during which the temperature signal is not received, progresses the same as the first cycle. In the fourth cycle, the room temperature signal is received during a period of the time T, (in this case the room temperature falls temporarily as at the time of opening and shutting a room door and window).In this case, however, the fuel supply and discharge mechanism is not operated because the gate is closed. With the room temperature signal coming in the time Tb set as T,, Tb, T2 and accepted, the next operation of GM1, GM2 is implemented and the fifth cycle begins with the gate closing, so that an automatic control is smoothly maintained to ensure stable and fail-free combustion.

It is desirable to determine, through prior experiments or according to experience, the most suitable lengths of the time T, and T2 in accordance with characteristics of fuel and other conditions for its use and apply them in the most suitable way for conditions at each occasion.

A time from the completion of a cycle of operation of the fuel supply and discharge mechanism to the consumption of unlit part of the fuel in the furnace can be used as the time T,. This can prevent a discharge of the unlit fuel, which can occur when the operation is implemented too early. In this case or another to maintain a fire force without a fall in force, it is desirable to set the time T, based on the assumption that it ensures the most appropriate or nearly so combustion state under certain operational conditions.

Similarly, it is desirable to set the time T2 based on the assumption that it ensures the most appropriate or nearly so combustion state under certain operational conditions.

This invention presents a method and apparatus for controlling a solid furnace which prevents discharge of unburnt fuel caused by too early an operation of the fuel supply and discharge mechanism, prevents extinguishing of the combustion source caused by too late an operation of the fuel supply and discharge mechanism, and ensures stable and secure automatic operation, so that it can avoid personal vigilance and operation labour and has great practical effects. The furnace is automatically kept alight, using such solid fuel as coal, powdered coal and coke. The invention is applicable to stoves to warm up the room air with a direct load, and to boilers to heat water with a direct load for room heating and supply of hot water.

Claims (12)

1. A method of controlling a furnace using solid fuel, the furnace having a fuel supply and discharge mechanism comprising a fuel supply means to supply the fuel to the furnace and ash discharge means to remove ash from the furnace, the combustion inside the furnace being controlled by the fuel supply and discharge mechanism, wherein if an operation signal for the fuel supply and discharge mechanism is received during the time T, (as herein defined) counted from the start of the operation of the fuel supply and discharge mechanism, the signal is not accepted and the fuel supply and discharge mechanism is not operated; the fuel supply and discharge mechanism is operated by acceptance of the operation signal when received after the lapse of the time T,; and the fuel supply and discharge mechanism is operated even in the absence of the operation signal after the lapse of the time T2 (as herein defined) from the said start.

2. A method as claimed in Claim 1, wherein the operation signal is a signal showing a load temperature.

3. A method as claimed in Claim 1 or 2, wherein the fuel supply means is a fuel supply fire grate, the ash discharge means is an ash discharge fire grate, a single operation of the fuel supply and discharge mechanism oscillating the ash discharge fire grate in the pre-determined number and the fuel supply fire grate in the pre determined number.

4. A method of controlling a furnace using a solid fuel, the furnace having a fuel supply and discharge mechanism comprising a fuel supply means to supply the fuel to the furnace and ash discharge means to remove ash from the furnace, the combustion inside the furnace being controlled by the fuel supply and discharge mechanism, wherein a load temperature is checked to be within a safety range, lighting is confirmed, the completion of a single operation of the fuel supply and discharge mechanism is confirmed, an operation signal is not accepted if received before the lapse of the time T1 (as herein defined) counted from the start of the operation of the fuel supply and discharge mechanism, the safety check is repeatedly implemented, a gate for the operation signal is opened after the lapse of the time T1, the safety check and the lighting confirmation are repeatedly implemented until the operation signal is received, the fuel supply and discharge mechanism is operated in a certain operational pattern with the operation signal accepted when received, and the fuel supply and discharge mechanism is operated even in the absence of the operation signal after the lapse of the time T2 (as herein defined) from the start.

5. A method as claimed in Claim 4, wherein the certain operational pattern is a certain operational pattern selected from a memory circuit for operational patterns of the fuel supply and discharge mechanism in accordance with its operational conditions.

6. A method of controlling 2 solid fuel burner substantially as herein described with reference to the accompanying drawings.

7. An apparatus for burning a solid fuel comprising a furnace for the fuel and a fuel supply and discharge mechanism comprising a fuel supply means to supply the fuel to the furnace, the apparatus having means for controlling combustion inside the furnace, the control means controlling the fuel supply and discharge mechanism and comprising a time measuring means to count a time from the start of the operation of the fuel supply and discharge mechanism, a gate circuit to reject an operation signal until the time T, (as herein defined) is counted by the time measuring means and to accept an operation signal between the elapse of time T, and the time T2 (as herein defined) an operation circuit to accept an operation signal and to operate the fuel supply and discharge mechanism in a certain operational pattern, a regularly working operation circuit to operate the fuel supply and discharge mechanism even in the absence of the operation signal after the time T2 is counted from the start, and a re-set circuit to reset the counting time of the time measuring means when the fuel supply and discharge mechanism is operated.

8. An apparatus as claimed in Claim 6, wherein the operation signal is a signal which is generated by a thermometer measuring the temperature of the furnace.

9. An apparatus as claimed in Claim 6 or 7, wherein the fuel supply means is a fuel supply fire grate, the ash discharge means is an ash discharge fire grate, and a driving means is provided to oscillate the fuel supply fire grate and the ash discharge fire grate separately.

1 0. An apparatus as claimed in Claim 6, 7 or 8, wherein the certain operational pattern is a certain operational pattern to be selected from a memory circuit for operational patterns of the fuel supply and discharge mechanism in accordance with its operational conditions.

11. An apparatus as claimed in any one of Claims 6 to 9, wherein a circuit is provided for repeating the safety check to ensure a load temperature to be within a safety range and the lighting confirmation between the start and acceptance of the operation signal.

12. An apparatus for burning a solid fuel in a solid fuel burner substantially as herein described with reference to the accompanying drawings.