GB2120366A - Electrode steam boiler - Google Patents

Abstract

An electrode steam boiler is provided with an electrode 22 capable of sensing a predetermined upper water level and emitting an actuating signal when this is reached and an electrode 24 capable of sensing a predetermined lower water level and emitting an actuating signal when this is reached. The signal from the upper sensing electrode may be used to actuate, for example, a relay causing the pump to be switched off thereby preventing overfilling of the boiler. The chemical dosing pump may also be actuated by the latter electrode which will, while the water remains at the upper sensor level, inject a controlled amount of salt into the water thereby increasing its conductivity. <IMAGE>

Description

SPECIFICATION Electrode steam boiler This invention relates to an improved electrode steam boiler and in particular relates to an improved control system for use therewith.

Electrode steam boilers are employed for the industrial production of steam by the passage of electricity directly through water from electrodes immersed therein. The rate of steam production is governed by controlling the water level within the boiler: the higher the water level, and therefore the greater depth of electrode immersed, the greater the power input and thus steam production.

The conventional control system for such boiler often comprises a system of relays actuated by sensing the electrical power consumption to cause water to be expelled from the boiler when the power consumption rises above a pre-set limit, and more water to be introduced into the boiler when the power consumption drops below a preset limit.

Since pure water is a poor conductor of electricity, in areas where the water is soft, that is contains few dissolved salts, it is usually necessary to add salts to the water in order for the electrode steam boiler to operate satisfactorily. As time goes on, and steam is produced, salts dissolved in the water are concentrated leading to excessive power consumption at low water levels within the boiler and, possibly, electrode damage.

To prevent this the operator must periodically shut down the boiler temporarily and discharge the concentrated liquor within it to waste.

Where insufficient salt is present or added to the water the pre-set power consumption limit will not be reached and the pump will therefore continue to fill the boiler until it is overfilled. Again the operative must watch for this condition and take appropriate remedial action.

The invention seeks to provide a control system for use with electrode steam boilers which reduces or overcomes the above disadvantages.

According to a first aspect of the present invention an electrode steam boiler is provided with an electrode capable of sensing a pre-determined upper water level and emitting an actuating signal when such pre-determined upper water level is reached.

According to a second aspect of the present invention an electrode steam boiler is provided with an electrode capable of sensing a predetermined lower water level and is capable of emitting an actuating signal when said predetermined lower level is reached. Preferably, both sensing electrodes are employed in the same electrode steam boiler.

The signal from the upper sensing electrode may be used to actuate various control circuits.

For example it may actuate a relay causing the pump to be switched off thereby preventing overfilling of the boiler. The signal from the upper electrode may also be used to actuate a dosing pump which will, while the water remains at the upper sensor level, inject a controlled amount of salt into the water within the boiler thereby increasing its conductivity. Once the conductivity is increased to a level at which steam generation is sufficient, the water will boil off and the level drop below the preset upper level thereby discontinuing the actuating signal and switching off the dosing pump.

The lower electrode may also be used to actuate the various control circuits. For example, if the liquor within the electrode is becoming too concentrated through build-up of salts by evaporation the water level will drop below the optimum value until it reaches the pre-determined limits at which the low electrode is actuated. The actuating signal can then be used to control an auxiliary solenoid blow-down valve causing a controlled amount of the concentrated liquor to be discharged to waste, thereby lowering the power consumption causing the normal cdntrol circuit of the boiler to actuate the pump and supply fresh water to the boiler thereby reducing the concentration of salts to acceptable levels.

Thus, using both aspects of the present invention, it is possible for the operation of an electrode steam boiler to be self-regulating in most of the conditions normally met, and not require the constant attention of an operator.

The electrodes may be positioned in any suitable manner. For example, one convenient way of mounting the electrode is to connect an external cylinder to the boiler with upper and lower water connections to the boiler so that the level of water within the external cylinder will be the same as that within the boiler. The electrodes may then be mounted within the external cylinder which facilitates access to them for adjustment and electrical connections.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an elevational view of an electrode steam boiler modified in accordance with the invention; and Figure 2 is a circuit diagram of a suitable control circuit for use with the boiler of Figure 1.

Referring to the drawings, Figure 1 illustrates an electrode steam boiler 10 and its control panel 12. The boiler is modified by the addition of an external cylinder 14 communicating with the interior of the boiler at points 16 and 18 above the highest and, respectively, below the lowest operating water levels of the boiler. The water level 20 within the cylinder 14 will be the same as that within the interior of the boiler 10. Two probe electrodes 22 and 24 are provided with the electrode 22 being set at a height corresponding to the desired upper limit of the water level and the electrode 24 being set at a level which corresponds with the desired lower limit of the water level.

Figure 2 illustrates the control circuitry which has the conventional high and low level relays operated in accordance with the sensed power consumption, LCR1 to LCR4. The upper limit electrode 22 is connected to a water level control relay 26 which has its normally closed contacts in the pump circuit. Thus, the pump 28 operates according to its conventional control circuit only while the electrode 22 is not actuated by the water level reaching its preset upper limit. Should this occur, the relay 26 operates to disconnect the pump circuit and close its normally open contact which is connected to a relay 30 which actuates a chemical dosing pump 32. The latter injects a small controlled quantity of salt into the liquid within the boiler, by increasing its conductivity, while the water level is at or above its preset limit.

Thus the effect of the upper sensing electrode 22 is to prevent automatically overfilling of the boiler when water that is too soft for adequate conduction is employed, and additionally take steps to remedy the situation by dosing the water with salt until conductivity rises to a level allowing the boiler to operate normally. Once this occurs, steam will be generated and the water level will drop until the chemical dosing metre is deactivated and the pump circuit restored once again to the control of the conventional relays LCR1 to LCR4.

The lower electrode 24 is connected to a second water level control relay 34 whose normally closed contact is connected via a contact ammeter 36 to a time delay relay 38 controlling the solenoid blow down valve 40. The blow down valve 40 is auxiliary to the main boiler blow down valve 42 and may have an adjustable needle valve 46 in circuit with it for manual adjustment, to suit particular boiler conditions, of the blow down rate achieved by the valve 40.

In operation, should the liquid within the boiler become too concentrated with impurities and its conductivity rise above acceptable limits, maintaining the sensed power within its preset limits will cause the water level progressively to drop as the more concentrated solution becomes capable of sustaining the load at lower and lower liquid levels. Once the preset lower limit determined by the height of the electrode 24 is reached the signal from the electrode 24 is discontinued and the relay 34 assumes its normally closed position (as illustrated in Figure 2). If, at the same time the current consumption of the electrodes of the boiler is at or above a preset limit as set by the contact ammeter 36, the relay 38 is energised. The latter is a time delay relay and, provided the signal persists longer than the time delay period of the relay, the solenoid blow down valve 40 opens. This causes a quantity of the concentrated liquor within the boiler to be discharged to drain immediately iowering the power consumption of the boiler and causing the normal control circuitry to activate the pump and inject fresh water within to the boiler thereby diluting the concentrated liquor and restoring normal operating conditions.

As can be seen from the above, the control circuitry according to the invention enables an electrode steam boiler to be largely self-regulating and avoid the problems of insufficiently conductive or over conductive water which have hitherto required over-seeing and manual correction.

Claims (8)

1. An electrode steam boiler which includes an electrode capable of sensing a predetermined upper or lower water level and emitting an actuating signal when such predetermined water level is reached.

2. A boiler as claimed in claim 1 having electrodes for sensing both an upper and a lower predetermined water level.

3. A boiler as claimed in claim 1 or 2 in which the signal from the upper sensing electrode is used to actuate a relay causing a water filling pump to be switched off thereby preventing over filling of the boiler.

4. A boiler as claimed in any one of claims 1 to 3 in which the signal from the upper electrode is used to actuate a dosing pump such that while the water remains at the upper sensor level a controlled amount of salt is injected into the water thereby increasing its conductivl-ty.

5. A boiler as claimed in any one of claims 1 to 4 in which the lower level actuating signal controls an auxiliary solenoid blow down valve causing a controlled amount of concentrated liquor to be discharged to waste thereby lowering the power consumption and in turn leading to a fresh supply of water to be pumped into the boiler.

6. A boiler as claimed in any one of claims 1 to 5 in which the electrodes are mounted on an -external cylinder connected to the main boiler with both upper and lower water connections so that the level of water within the external cylinder is the same as that within the boiler.

7. A boiler as claimed in any one of claims 1 to 6 in which the electrodes are probe electrodes producing an electrical signal.

8. An electrode steam boiler substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.