Gas separation: processes – With control responsive to sensed condition – Electric or electrostatic field
Patent
1995-10-12
1998-01-13
Chiesa, Richard L.
Gas separation: processes
With control responsive to sensed condition
Electric or electrostatic field
95 7, 95 58, 95 71, 95 81, 96 22, 96 23, 96 52, 96 74, B03C 3013
Patent
active
057074224
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for use in an electrostatic precipitator unit comprising discharge electrodes and collecting electrodes between which a varying high voltage is maintained by means of a pulsating direct current supplied thereto, of controlling, with a view to cleaning an incoming dust-laden gas, the supply of conditioning agent to the incoming dust-laden gas.
The method is especially well suited when the pulsating direct current has the form of a pulse train which is synchronised with the frequency of the mains voltage (e.g., a commercially available power supply) and in which the pulses are generated by supplying a part of a half wave of the mains voltage by means of a phase-angle-controlled rectifier (thyristor) after step-up transformation, to the electrodes of the precipitator, whereupon a plurality of periods of the mains voltage are allowed to pass without any current being supplied to the electrodes. A part of a half wave is thereafter again supplied, followed by a plurality of periods without any current, and so forth.
The method can be used both for optimizing the amount of conditioning agent and for tactical decisions of whether conditioning agent should be supplied at all.
TECHNICAL BACKGROUND
Electrostatic precipitators are often the most preferred dust separator option, especially for flue gas cleaning. They have a robust design and are highly reliable in operation. Moreover, they are very efficient, not seldom having a separation efficiency of above 99.9%. Since, as compared with textile barrier filters, electrostatic precipitators involve low costs of operation as well as a low risk of breakdown and stoppage owing to malfunction, they are the natural choice in many contexts.
When dust of high resistivity is to be separated, the comparison with textile barrier filters sometimes turns out different. In such cases of operation, it is often necessary, when using electrostatic precipitators, to operate with extremely unfavourable process parameters because of the risk of breakdowns in the dust layer building up on the collecting electrodes. This results in the emission of charges and dust from the collecting electrodes, what is generally known as back corona.
As early as the beginning of this century it was noted that additives could favourably affect The separation, e.g. by reducing the resistivity of the dust. The addition of water or sulphur trioxide is an example of this, and is discussed e.g. in U.S. Pat. No. 1,909,825 and U.S. Pat. No. 3,689,213.
To optimize operation and reduce energy consumption while improving the separation, several methods have been suggested for feeding current pulses to the filter. Examples of this are given in U.S. Pat. No. 4,052,177 and U.S. Pat. No. 4,410,849. The former publication suggests feeding pulses which are in the order of microseconds, which means that the rectifiers become very expensive. The latter publication suggests using pulses in the order of milliseconds, which can be achieved fairly easily by selectively controlling common thyristor rectifiers fed with alternating current of mains frequency.
The need to control the amount of conditioning agent is already disclosed in U.S. Pat. No. 1,909,825, proposing that an increasing current in the precipitator shall lead to reduced supply of water and, conversely, that a decreasing current shall lead to increased supply of water. Alternative embodiments consist of supplying liquid or superheated steam, optionally in combination with cold air. In special cases, heating or cooling, combined with the addition of conditioning agent, may prove suitable.
More recent control principles are based on a number of measuring parameters. U.S. Pat. No. 4,779,207 suggests adding conditioning agent so as to maintain the power fed to the precipitator constant. In U.S. Pat. No. 3,665,676, the amount of conditioning agent is directly related to the gas flow. U.S. Pat. No. 3,993,429 suggests making the amount of conditioning agent supplied dependent on the amount of fuel, coal, that
REFERENCES:
patent: 1909825 (1933-05-01), Hahn et al.
patent: 3665676 (1972-05-01), McKewen
patent: 3689213 (1972-09-01), Guerrieri
patent: 3993429 (1976-11-01), Archer
patent: 4052177 (1977-10-01), Kide
patent: 4267502 (1981-05-01), Reese et al.
patent: 4311491 (1982-01-01), Bibbo et al.
patent: 4410849 (1983-10-01), Ando
patent: 4626261 (1986-12-01), Jorgensen
patent: 4770674 (1988-09-01), Tellini et al.
patent: 4779207 (1988-10-01), Woracek et al.
patent: 4987839 (1991-01-01), Krigmont et al.
patent: 5217504 (1993-06-01), Johansson
patent: 5288303 (1994-02-01), Woracek et al.
patent: 5311420 (1994-05-01), Zarfoss et al.
patent: 5477464 (1995-12-01), Jacobsson
Jacobsson Hans
Porle Kjell
ABB Flakt AB
Chiesa Richard L.
LandOfFree
Method of controlling the supply of conditioning agent to an ele does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of controlling the supply of conditioning agent to an ele, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of controlling the supply of conditioning agent to an ele will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-322733