GB1594139A

GB1594139A - Plant for aspiranting air containing harmful substances from large buildings more particularly secondary dust extraction plant in steelworks

Info

Publication number: GB1594139A
Application number: GB5181377A
Authority: GB
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1976-12-14
Filing date: 1977-12-13
Publication date: 1981-07-30
Also published as: DE2657067A1; JPS5375106A; FR2374099A1; DE2657067C3; FR2374099B1; DE2657067B2

Description

(54) PLANT FOR ASPIRATING AIR CONTAINING HARMFUL SUBSTANCES FROM LARGE BUILDINGS, MORE PARTICULARLY SECONDARY DUST EXTRACTION PLANT IN STEELWORKS (71) We, MANNESMANN AKTIENGESEL LSCHAFT, a joint stock company organised under the laws of Germany, of Mannesmannufer 2, 4 Dusseldorf 1, Germany, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following state ment This invention relates to a plant for aspirating air containing harmful substances from large buildings and similar structures and in particular to a plant of the type comprising a fan provided with a regulating arrangement, and a collecting duct with a plurality of hoods each fitted with a throttle valve.Such a plant may be used for secondary dust extraction in a working shed or bay of a steel-works or a blast furnace casting bay.

In a one plant of this kind which has been proposed, in addition to plant for the primary dust extraction from converter exhaust gases, a central secondary dust extraction for a working bay is provided wherein the hoods, connected to the collecting duct, are arranged above the various sources of dust in the working bay. The valves are so controlled that only those throttle valves whose hoods at that instant are in the region of a "cloud of dust" are in the fully open position. The central fan which is designed for the most disadvantageous operational situation in which all the hoods of the plant are open, runs at part load with some hoods closed by the throttle valves. The saving in energy at the fan drive obtained by the "open and shut" control of the throttle valves in accordance with this process is however, only very modest.One reason is that the throttle valves are only always fully open or fully closed, in other words continuous adjustment is not used, and a second reason is that there is more aspiration than previously at the extraction points which are opened.

The invention has as its object to provide a plant of the tyre specified with which it is possible to save a substantial amount of energy.

Accordingly,the present invention provides a plant for aspirating air containing harmful substances from large buildings, the plant comprising a fan provided with a regulating device and a collecting duct provided with a plurality of aspirating hoods each fitted with a throttle valve, each throttle valve is bridged by a continuously open test flow duct which is provided with a continuously functioning unit for measuring the harmful substances content of the aspirated air, each harmful substances measuring unit is connected to the regulating drive of the associated throttle valve. A pressure meter for a controller influencing the regulating arrangement of the fan may be provided, associated with an aspirating hood for example in one of the test flow ducts.

Thus with the plant according to the present invention it is possible to operate under the simultaneous influence of two controllers. One controller ensures that basically only as much carrier air is aspirated at each hood as the instantaneous content of harmful substances in the air requires, (for example the specific CO content or dust content of the working bay air may be measured). The other controller, additionally ensures that the complete plant can be operated in an energy-saving fashion with a minimum of carrier air.

The particularly large difference in the throughput quantities of carrier air to be expected with the plant according to the present invention on the one hand and on the other hand the fact that the invention is concerned above all with fans of relatively large driving power, show that it is advantageous to use variable-speed fans so that the aforesaid regulating arrangement of the fan preferably acts to vary the rotational speed of the fan.

But it is also possible to save substantial quantities of energy according to the present invention when using fans with characteristic stabilisation and variable-setting valve regulation, although the efficiency is lower in the case of part-load operation.

Rapid measurement of the content of harmful substances and rapid opening of the throttle valves is essential for operating the plant according to the invention. In order to ensure that aspiration is carried out from the begin ning, in the case of a plant where harmful substances is produced suddenly, it is advantageous for the operation of such a plant, to bring the mouthpieces of the test flow ducts as close as possible to the source of harmful substances, and possibly to distribute a plurality of mouthpieces over the source area, and also to open the throttle valves completely at a high speed by a processilependent anticipa tory control.Only the indication of harmful substances in the working bay air, which is continually tested by the assoicated harmful substances measuring unit, would then initiate the automatic control operation so that the throttle valve closes as far as is required by the intended fine adjustment of this valve.

The invention will now be further described by way of example with reference to the accompanying drawings, in which Figure 1 is a diagram of a dust extraction plant with three aspirating hoods, a central filter and a central fan with rotational speed adjustment, Figure 2 shows the characteristic chart of a fan with characteristic stabilisation and variable-angle valve control with the plant characteristics plotted.

The plant comprises a collecting duct 2 of a dust extraction plant (Figure 1) through which air flows in the direction indicated by arrow 1 and which leads to a dust filter 3 and from there by way of a fan 4 to an outgoing air duct 5. Between the fan 4 and its drive motor 6 there is arranged a gear unit 7 with a variable transmission ratio, and which is adjusted by signals to vary the drive to the fan or, when using fans with variable-angle control, to adjust such fans.

At the suction side, three aspirating hoods 8,9 and 10 open into the collecting duct 2 and these are arranged, for example in a steciworks working bay above a pig iron mixer, a refilling pit and surroundings of the converter.

Each of the three aspirating hoods is provided with a throttle valve 11 which is adapted to be steplessly adjusted by a regulating drive 12. The throttle valves 11 are each bridge by a continuously open test flow duct 13 which is narrow in relation to the crosssection of the associated hood. The mouthpiece 14 of the test flow duct 13 is situated upstream of edge 15 of the hood 8,9 or 10. In this example a photometric dust measuring unit 16 which indicates dust valves without any delay is a component part of the test flow duct 13. In other examples, a CO measuring unit could be used in place of this dust measuring unit for indicating the harmful substances content of the air being examined. From the unit 16, a measuring line leads to a controller 17 which is connected with the regulating drive 12 of the throttle valve 11 to form a control circuit 18.

A pressure meter 19 is arranged at the test flow duct of the hood 10. From this suction pressure meter a measuring line leads to a controller 20 which contacts the regulating arrangement 7 of the fan 4.

The filter 3 and the fan 4 of the plant shown in Figure 1 are designed so that in the fully open position of all the throttle valves 11, each hood 8,9 or 10 has a sufficent air throughput V. In the fan characteristic chart illustrated in Figure 2 plant characteristic line 21 for the aforesaid state of the fully open situation of all the throttle valves 11 , has an operating point A which is obtained in the case of this first assumption. This point usually corresponds to the design point of the fan, and in the case considered is H = 5 and V= 100%.Contrary to the first assumption, there is shown as the second assumption in Figure 1 the example that the throttle valve 11 of the hood 8 is fully closed and the throttle valve of the hood 9 is half closed, so that the throughpout quantity in the collecting duct 2 and in the fan 4 need amount to only 50% of the maximum quantity.

The assumption of operation with 50% throughput quantity requires that the dust produced is completely aspirated with the hoods 9 and 10, so that with a larger air throughput through the relevent hoods too much carrier air would be aspirated, which costs unnecessary energy.

The adjustment of the throttle valves according to the second assumption in Figure 1 is initiated by the measurement signal of the dust measuring unit 16 and effected by the control circuit 18. As a result there is another, steeper plant characteristic line 22, so that the point A migrates towards the point A'. Then if the pressure were kept constant as in the state of the art, the throttle valve control would regulate towards point B. In carrying out this measure, more carrier air is aspirated at the hood 10 than in the open position of all the valves. According to the invention this increased aspiration is prevented in that the pressure in the test flow duct of the hood 10 is kept constant by the control circuit 22. As a result, the operating point C is on the plant characteristic 22.The saving is obtained from the product AV . All, allowing for the respective efficiency in each case.

WHAT WE CLAIM IS: 1. A plant for aspirating air containing harmful substances from large buildings, the plant comprising a fan provided with a regulating device and a collecting duct provided with a plurality of aspirating hoods each fitted with a throttle valve, each throttle valve is bridged by a continuously open test flow duct which is provided with a continuously functioning unit for measuring the harmful substances content of the aspirated air, each harmful substances measuring unit is connected to the regulating drive of the associated throttle valve.

2. A plant as claimed in Claiml , wherein a pressure meter for a controller which controls the regulation of the fan is associated with an aspirating hood.

3. A plant as claimed in Claim 1, wherein the regulation of the fan comprising a device for varying the rotational speed.

4. A plant as claimed in Claim 2 or 3, wherein the pressure meter is connected in a test flow duct.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. close as possible to the source of harmful substances, and possibly to distribute a plurality of mouthpieces over the source area, and also to open the throttle valves completely at a high speed by a processilependent anticipa tory control. Only the indication of harmful substances in the working bay air, which is continually tested by the assoicated harmful substances measuring unit, would then initiate the automatic control operation so that the throttle valve closes as far as is required by the intended fine adjustment of this valve. The invention will now be further described by way of example with reference to the accompanying drawings, in which Figure 1 is a diagram of a dust extraction plant with three aspirating hoods, a central filter and a central fan with rotational speed adjustment, Figure 2 shows the characteristic chart of a fan with characteristic stabilisation and variable-angle valve control with the plant characteristics plotted. The plant comprises a collecting duct 2 of a dust extraction plant (Figure 1) through which air flows in the direction indicated by arrow 1 and which leads to a dust filter 3 and from there by way of a fan 4 to an outgoing air duct 5. Between the fan 4 and its drive motor 6 there is arranged a gear unit 7 with a variable transmission ratio, and which is adjusted by signals to vary the drive to the fan or, when using fans with variable-angle control, to adjust such fans. At the suction side, three aspirating hoods 8,9 and 10 open into the collecting duct 2 and these are arranged, for example in a steciworks working bay above a pig iron mixer, a refilling pit and surroundings of the converter. Each of the three aspirating hoods is provided with a throttle valve 11 which is adapted to be steplessly adjusted by a regulating drive 12. The throttle valves 11 are each bridge by a continuously open test flow duct 13 which is narrow in relation to the crosssection of the associated hood. The mouthpiece 14 of the test flow duct 13 is situated upstream of edge 15 of the hood 8,9 or 10. In this example a photometric dust measuring unit 16 which indicates dust valves without any delay is a component part of the test flow duct 13. In other examples, a CO measuring unit could be used in place of this dust measuring unit for indicating the harmful substances content of the air being examined. From the unit 16, a measuring line leads to a controller 17 which is connected with the regulating drive 12 of the throttle valve 11 to form a control circuit 18. A pressure meter 19 is arranged at the test flow duct of the hood 10. From this suction pressure meter a measuring line leads to a controller 20 which contacts the regulating arrangement 7 of the fan 4. The filter 3 and the fan 4 of the plant shown in Figure 1 are designed so that in the fully open position of all the throttle valves 11, each hood 8,9 or 10 has a sufficent air throughput V. In the fan characteristic chart illustrated in Figure 2 plant characteristic line 21 for the aforesaid state of the fully open situation of all the throttle valves 11 , has an operating point A which is obtained in the case of this first assumption. This point usually corresponds to the design point of the fan, and in the case considered is H = 5 and V= 100%.Contrary to the first assumption, there is shown as the second assumption in Figure 1 the example that the throttle valve 11 of the hood 8 is fully closed and the throttle valve of the hood 9 is half closed, so that the throughpout quantity in the collecting duct 2 and in the fan 4 need amount to only 50% of the maximum quantity. The assumption of operation with 50% throughput quantity requires that the dust produced is completely aspirated with the hoods 9 and 10, so that with a larger air throughput through the relevent hoods too much carrier air would be aspirated, which costs unnecessary energy. The adjustment of the throttle valves according to the second assumption in Figure 1 is initiated by the measurement signal of the dust measuring unit 16 and effected by the control circuit 18. As a result there is another, steeper plant characteristic line 22, so that the point A migrates towards the point A'. Then if the pressure were kept constant as in the state of the art, the throttle valve control would regulate towards point B. In carrying out this measure, more carrier air is aspirated at the hood 10 than in the open position of all the valves. According to the invention this increased aspiration is prevented in that the pressure in the test flow duct of the hood 10 is kept constant by the control circuit 22. As a result, the operating point C is on the plant characteristic 22.The saving is obtained from the product AV . All, allowing for the respective efficiency in each case. WHAT WE CLAIM IS:

1. A plant for aspirating air containing harmful substances from large buildings, the plant comprising a fan provided with a regulating device and a collecting duct provided with a plurality of aspirating hoods each fitted with a throttle valve, each throttle valve is bridged by a continuously open test flow duct which is provided with a continuously functioning unit for measuring the harmful substances content of the aspirated air, each harmful substances measuring unit is connected to the regulating drive of the associated throttle valve.

5. A plant as claimed in any of the preced

ing claims, wherein the mouthpiece of the test flow duct is arranged upstream of the edge of the hood.

6. A plant as claimed in Claim 5, wherein the test flow duct is provided with a plurality of mouthpieces which are distributed over the hood cross-section.

7. A method of operating a plant according to any one of Claims 1 to 6, wherein the throttle valves are fully opened from the closed position by rapid action adjustment, and subsequently the precise movement to the desired position is carried out.

8. A plant substantially as hereinbefore described with reference to the accompanying drawings.