GB2342431A

GB2342431A - Fume purification system for a furnace

Info

Publication number: GB2342431A
Application number: GB9817990A
Authority: GB
Inventors: Mark Riyahd Sale
Original assignee: J Mcintyre
Current assignee: J Mcintyre
Priority date: 1998-08-19
Filing date: 1998-08-19
Publication date: 2000-04-12
Also published as: GB9817990D0

Abstract

A fume purification plant (FPP) 16 for a furnace (F) 10 comprises a plurality of ceramic candle filters 18 and a monitoring system (FPPMS) to monitor the condition of each candle 18 or series of candles 18 to detect when a candle 18 or a series of candles 18 is faulty. The monitoring system (FPPMS) comprises means for generating a first continuous waveform of differential pressure across the candle 18, or series of candles 18 and generating a second waveform at predetermined intervals when a burst of air pressure is applied to the inside of each candle 18 to blow of all the dust and powder clinging to the outside wall of each candle 18. By comparing the first and second waveforms the faulty candle 18 or series of candles 18 can be identified.

Description

IMPROVEMENTS IN OR RELATING TO FUME PURIFICATION SYSTEMS The present invention relates to fume purification systems and more particularly to a method and apparatus for monitoring the efficiency of a fume purification apparatus.

In a known fume purification apparatus exhaust gases from, for example, a furnace are fed to the apparatus which gases are usually extremely hot.

The apparatus may include means for cooling said gases and also means for extracting particles from the gases.

One said means for extracting particles from the exhaust gases is a ceramic filter. This comprises a large number of filter elements or candles. The filter elements will be referred to hereafter as candles.

Each candle comprises an elongated closed tube structure through which exhaust gases are drawn. The principle of operation is that the candles, which are made from pervious ceramic material, trap the small particles on their outside surfaces allowing clean air to be extracted from the inside of the candles.

To maintain efficiency of the fume purification plant, all of the candles must be in good condition. If one candle becomes faulty, or if another fault occurs in the plant, then contaminated air will be exhausted from the fume purification plant and vented to atmosphere. This will require the plant to be shut down until the fault can be identified.

In a typical fume purification plant there may be, for example, 2,400 candles and identifying a faulty candle or any other fault can be an extremely lengthy exerc. e.

Whilst the fault is being rectified the furnace, or incinerator, may not be able to be run and may have to be placed in a standby mode with no new scrap material being introduced into the furnace.

Although this may only occur occasionally, when it does occur the cost of shutting down the furnace, or incinerator, can be substantial.

It is an object of the present invention to provide a method and apparatus for monitoring the performance of a fume purification plant, to identify faulty parts and to enable rectification of faults whilst the fume purification plant is still functioning.

The present invention, therefore, provides a fume purification plant for a furnace said fume purification plant comprising a plurality of candles and including monitoring means for continuously monitoring the condition of each candle, or series of candles, said monitoring means including means for detecting when a candle, or series of candles, is faulty.

Preferably, said monitoring means comprises means for detecting differential pressure across a candle, or series of candles, to produce a first continuous output in waveform and means for analysing said continuous output waveform to indicate a fault condition.

Preferably, a further second waveform is generated comprising waveform showing air pressure connected to each candle, or series of candles, during a blow down operation, said waveform being analysed in conjunction with said first waveform, said second waveform, indicating the candle, or series of candles, being subjected to said blow down pressure at a specified time period.

By analysis of the two waveforms, the first differential pressure waveform can be analysed only at the time period during which the blow down pressure is applied. The other peaks which may occur in the system due, for example, to increases or decreases in operational fan speed, or sudden increases in pressure from the furnace, can be eliminated from the analysis.

Preferably, said series of candles comprises a row of candles, all of which are subjected to a blow down pressure at the same time.

The present invention also provides a method of monitoring the condition of a candle, or a series of candles, in a fume purification plant, said method comprising generating a first continuous output waveform of differential pressure across the candle, or series of candles, generating a second further output waveform comprising a graph of flow down pressure provided to each respective candle, or series of candles, and including the step of comparing both first and second output waveforms and identifying by said comparison a faulty candle, or series of candles.

This also provides a check that the blow down air valves are working correctly.

Embodiments of the present invention will now be described, by way of example with reference to the accompanying drawings in which: Figure 1 shows diagnostically a furnace system incorporating a fume purification system in accordance with the present invention, Figure 2 shows diagnostically an arrangement of pods within the fume purification system of figure 1, illustrating the fume paths through the pods and also the dust conveyor removal system, Figure 3 illustrates the acid neutralising system associated with the fume purification system of figure 2, Figure 4 shows a pod of figure 2 in greater detail, Figure 5 shows diagnostically a control system illustrating control of the flows down sequences and generation of the output diagnostic data and alarm system in accordance with the present invention; and Figures 6 and 7 show waveforms illustrating the operation of the control circuitry of the present invention in detecting faulty candles.

The present invention provides a smelting furnace and ceramic filter control and management system which incorporates a computer program, attaining the requirement to automatically alter the volume of flue gas extracted through a ceramic filter plant, maintaining the correct volumes of gas extraction during the charging, melting and holding cycles of the furnace. The program requirements to monitor the ceramic filter plant performance and provide continuous diagnostic information on the element condition, cleaning cycle and the continuous correct dosage of additives into the ceramic filter plant, as pertaining to effect legal airborne emissions to atmosphere.

The system is able to automatically compensate for changes in temperature and pressure both from within the furnace and the ceramic filter during operation by means of pressure sensors being fitted to the furnace chambers. The data from the pressure sensors is compared to the required set point within the computer program and by means of an electronic inverter coupled to the flue gas extraction fan, situated after the ceramic filter plant, may be automatically speeded up or slowed down. The speed of the flue gas extraction fan is monitored, as is the rate at which additives are injected into the filter plant. Additive injection is also controlled via an electronic inverter, therefore a ratio between gas extracted and chemical additive required is inserted into the computer program, allowing the automatic dosing of the filter plant to the correct level at all times.

The ceramic filter plant has distinct filter element banks or"Pods". Each individual pod is monitored for gas inlet temperature, differential pressure across the ceramic filter elements and for element cleaning manifold pressure. This data is scaled and presented against time in a line graph form and can be either real time or collated and is stored in files for a performance history to be achieved within the computer program. The computer program monitors the cleaning cycle of each filter pod one at a time and in series. The ceramic filter elements within each pod are arranged in column with pipework leading from a solenoid valve to each individual ceramic filter element. The ceramic element cleaning is by means of activating the solenoid valve, allowing a pulse of compressed air to enter the inside of a column of ceramic elements, therefore changing the air pressure within the elements, blowing off the matter which has been collected on the outer skin of the elements. As each individual solenoid valve is opened, compressed air pressure within the manifold drops, showing that the operation has been completed. The line graph for compressed air manifold pressure will show a series of troughs as each solenoid valve opens during the cleaning cycle, should there be an irregular gap between the troughs then this would indicate a solenoid failure. By counting the number of troughs from the cycle start until the gap appears, the individual solenoid can be identified on the filter plant. During this filter element cleaning cycle, particulate levels, after the filter elements, are monitored and recorded against time as described for the cleaning air manifold pressure. The resultant data can be presented against the graph showing the air pressure pulses. During the normal cleaning cycle, particulate levels at the pod exit should be relatively stable, should a rise in particulate occur, then this would indicate element failure.

It is possible to identify in which row the problems element (s) are located by observing the peak particulate emission level and comparing this to the manifold cleaning pulses, therefore giving a column number.

With reference now to the drawings, figure 1 shows a furnace 10 which may, for example, be a smelting furnace of known design.

Dirty exhaust gas is fed via exhaust outlet 12, assisted by fan 14 to a fume purification plant 16.

Therefore, purification plant 16 includes a ceramic filter 18 the exhaust output of which is fed to a chimney 20 via a further exhaust fan 22. A further outlet 24 is provided for dust and powder which is then bagged in bagging apparatus 26.

A fume plant purification monitoring system (FPPMS) 40 is connected to monitor the operation of the fume purification plant 16 as described in greater detail hereafter. The ceramic filter 18 is shown in greater detail in Figure 2 and comprises a plurality of pods (1 to 6) 182 each pod being substantially identical.

Exhaust gas fumes from furnace 10's input via inlets 184,196. The fumes, which include particulates from the furnace 10 and also powder (see figure 3), pass via respective tubes 188, 190 to the pods 182.

Each pod 182 comprises a ceramic filter complex 1820, a dust valve arrangement 1822, an exhaust duct 1824 and a preferably funnel shaped arrangement 1826 for collection of the dust and powder.

Additionally, associated with each funnel 1826 is a conveyor 1830. In the arrangement shown, two conveyors 1830 are provided, each serving three pods.

The conveyors are driven by motors 1840,1842,1844. Each conveyor 1830 is connected to the out put flue 24 (see figure 1), to convey the dust and powder to the bagging system 26.

The dust valve arrangement 1822 comprises an inlet 18221 for supply of compressed air, two being provided for this particular pod arrangement.

The dust valve arrangement allows via control valves and a timing arrangement (see figure 5), for each candle, or series of candles (see figure 4), to be blown in a required sequence.

Typical figures for fan speed, fan motor current, differential pressure, powder blow, furnace smelt pressure, furnace load pressure and filter inlet temperature are given in the drawing. The powder feed arrangement is shown in figure 3. Powder 30 typically sodium bicarbonate is stored in a silo 300 and fed via screw conveyor 302 driven by motor 304 to a mixing arrangement 306 where the powder 30 is mixed with air by a powder fan 308.

The air/powder mixture is then fed into the main exhaust outlet 12 from the furnace and serves to preserve the neutrality of the exhaust gases by neutralising the acidity.

A monitoring system on the exhaust gases is used to ensure that the powder flow rate is correct for neutralisation and figures for current powder screw feed powder, flow rate and total powder usage over a defined period are given for a typical arrangement.

With reference now to figure 4, a pod 182 is shown in greater detail.

The pod comprises an inlet 186 through which fumes and the air/powder mixture pass as indicated by arrow 1862. The dust valve arrangement 1822 comprises a plurality of dust valve blow tubes 18220. Each blow tube 18220 may be connected to blow air through a plurality of candles 18222 shown in dotted outline. Each candle 18222 comprises an elongated, hollow tube of ceramic material, closed at one end 18224 and open at the other end 18226.

The exhaust gases and powder 1862 pass through the ceramic filter 18222 from the outside 18228 to the hollow inside 18230 and in so doing the dust and powder is finely filtered and remains on the outside surface of the candle, the now clean exhaust gas passing via outlet 1824 to the chimney.

At predetermined intervals a blow down air pressure pulse burst is applied to each drive line 18220 in turn in a known order. The burst of air pressure is applied to the inside of each of the plurality of candles 18222 in the line of candles and serves to blow off all the dust and powder clinging to the outside wall 18228 of each candle.

The dust and powder falls down to conveyor 1830 which conveys it to the dust bag apparatus.

The ceramic filter arrangement 18 is provided with a respective sensor P1, P2 (see figure 5), which measures the differential pressure across the inlet side 186 and the outlet side 1824 as each blow down is performed. These measurement are processed in a processor 50, which also provides the timing sequences by means of timer 51.

With reference to figures 5,6 and 7, these waveforms show at a) the differential pressure and at b) the blow down pressure burst.

Figure 6 show a normal waveform pattern in which the differential pressure waveform is substantially uniform in value. The lines 60,62 indicate that there are a substantial number of blow down periods, these being numbered 1---M---N. N could be, for example 108, to provide 108 drive lines each, for example, having 12 ceramic candles giving a total of approximately 1300 candles. In a larger pod the numbers could be greater giving a total of 2600 candles.

In figure 7, however, at the Mth occurrence of the blow down a pulse (c) appears on waveform a) and this indicates that a candle in the Mth row is faulty.

This pulse (c) may appear as indicated, or if the candle is progressively becoming faulty, the pulse could grow in size. By suitable monitoring, as in differential pressure monitor 52, the pulse (c) can be detected and the row of candles can be pinpointed.

If, for example, the row is the fourth in succession on the pod in figure 4 which, for example, is pod 5 in figure 2, then the candle can be changed as follows. The pod 5 can be isolated by closure of values (not shown) to prevent passage of fumes and powder into pod No. 5, whilst allowing the other pods 1-4 and 6 to operate normally.

The pod can be opened and all of the candles in row 18220 inspected.

Since there are only, for example, 12 in the row it is relatively easy to inspect each candle and to ascertain which candle is faulty.

This is to be compared to the alternative which is to monitor the quality of the output fumes entering chimney 20 and to shut down the fume purification plant to identify, by inspecting all candles, any faulty candle.

Using the system of the present invention the operation of the furnace system does not have to be affected and the candles can be replaced only when faulty. Since inspection of candles by removal from their mountings can be responsible for damaging the candles then the removal and replacement of, for example, 2000 candles to inspect them will undoubtedly result in the damaging of one or more candles. Also defects may not always be apparent and therefore candles may be replaced which are perfectly functionable. By ensuring that only a limited number require to be inspected there is a much greater certainty of identifying a faulty candle before any undue exhaust contamination occurs.

The system of the present invention, therefore, has a substantial commercial and environmental value.

Claims

CLAIMS 1. A fume purification plant for a furnace said fume purification plant comprising a plurality of candles and including monitoring means for continuously monitoring the condition of each candle, or series of candles, said monitoring means including means for detecting when a candle, or series of candles, is faulty.
2. A fume purification plant as claimed in Claim 1 said monitoring means comprises means for detecting differential pressure across a candle, or series of candles, to produce a first continuous output in waveform and means for analysing said continuous output waveform to indicate a fault condition.
3. A fume purification plant as claimed in Claim 2 in which a further second waveform is generated comprising waveform showing air pressure connected to each candle, or series of candles, during a blow down operation, said waveform being analysed in conjunction with said first waveform, said second waveform, indicating the candle, or series of candles, being subjected to said blow down pressure at a specified time period.
4. A fume purification plant as claimed in Claim 3 in which said series of candles comprises a row of candles, all of which are subjected to a blow down pressure at the same time.
5. A method of monitoring the condition of a candle, or a series of candles, in a fume purification plant, said method comprising generating a first continuous output waveform of differential pressure across the candle, or series of candles, generating a second further output waveform comprising a graph of flow down pressure provided to each respective candle, or series of candles, and including the step of comparing both first and second output waveforms and identifying by said comparison a faulty candle, or series of candles.