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STUDY AND DEVELOPMEMT OF AN ELECTROSTATIC PRECIPITATOR FOR HOT GAS CLEAN-UP

Objective

THE AIM OF THIS RESEARCH IS TO STUDY THE FEASIBILITY OF A NEW TYPE OF DUST SEPARATOR COMBINING A CONVENTIONAL DUST SEPARATOR AND A PRECHARGER USING THE INJECTION OF A VAPORIZABLE AEROSOL;THIS CLEAN-UP METHOD WILL BE TESTED FOR SEVERAL TYPES OF SEPARATORS.

THE PROJECT WILL APPLY AT A REAL SCALE A NEW CONCEPT OF PRECHARGING INVENTED AT ONERA (FRANCE) AND STUDIED AT A REDUCED SCALE BY ECOPOL FROM 1982 TO 1985.THIS TECHNIQUE CONSISTS OF CHARGING THE PARTICULATES IN THE RAW GAS WITH IONS COMING FROM THE VAPORIZATION OF AN ELECTRICALLLY CHARGED WATER AEROSOL INTRODUCED INTO THE FLOW BY TINY SUPERSONIC NOZZLE INJECTORS FITTED WITH A CORONA POINT AND INJECTING AIR WITH A LOW HUMIDITY CONTENT.THE COLLECTION OF THE CHARGED PARTICULATES IS THEN PERFORMED BY A DUST SEPARATOR OF A TYPE BUILT BY LURGI GMBW AND MODIFIED,WITH THE ESSENTIAL SUPPORT OF THE UNIVERSITY OF PADERBORN,IN ORDER TO COLLECT THE CHARGED PARTICULATES.
A new technique for injecting electric charges into raw gas flows was used to precharge dust in various types of dust separator. The precharging unit consisted of a small supersonic nozzle with an orifice 3 mm in diameter at the end of a pipe fed with compressed air. Inside this device, an axial ionising high voltage needle produces a corona discharge between its point and the nozzle. The charge carriers are ejected into the raw gas flow by the drag force of the jet. The dust particles acquire an electric charge when crossing the ionic space charge formed when the jet mixes with the raw gas. A significant increase in collection efficiency was obtained in a polarised granular bed filter, with the raw gas at temperatures up to approximately 300 C. The most interesting result was obtained in a fabric filter, where the pressure drop for a given dust loading on the fabric was drastically reduced by precharging. An industrial scale test was then performed where it was shown that a precharging current as low as 10 uA was sufficient to decrease the cleaning frequency by 30% or to increase the air to cloth ratio by 10 to 30%. This result can open the way for a practical method of reducing capital investment in facilities using bag filters.

A new method for injecting electric charges into raw gas flows was used to precharge dust in varioustypes of dust separators. The improvement obtained by applying this method to various types of dust separators was studied.

A significant increase in collection efficiency was obtained in a polarised granular bed filter, with the raw gas at temperatures up to approximately 300 C. The improvements obtained in a conventional electrostatic precipitator and in 2 types of scrubbers could easily have been attained, at lower cost, by increasing the high voltage and the liquid to air ratio, respectively. The most interesting result was obtained in a fabric filter, where the pressure drop for a given dust loading on the fabric was drastically reduced by precharging.

An industrial scale test was performed with a fabric filter rated for 2,400 cubic metres of raw gas per hour. The maximum pressure drop across the filter was kept constant. It was shown that a precharging current as low as 10 uA was sufficient to decrease the cleaning frequency by 30%, or increase the air to cloth ratio by 10 to 30%.

A new method for injecting electric charges into raw gas flows was used to precharge dust in various types of dust separators. The improvement obtained by applying this method was first studied in the laboratory.
A significant increase in collection efficiency was obtained in a polarized granular bed filter with the raw gas at temperatures up to approximately 300 C.
The most interesting result was obtained in a fabric filter where the pressure result was obtained in a fabric filter where the pressure drop for a given dust loading on the fabric was drastically reduced by precharging. An industrial scale test was performed with a fabric filter rated for 2400 m{3} of raw gas per hour. The maximum pressure drop across the filter was kept constant. It was shown that a precharging current as low as 10 uA was sufficient to decrease the cleaning frequency by 30%, or increase the air to cloth ratio by 10 to 30%.
THE PROJECT HAS BEEN PROPOSED TO STUDY THE IMPROVEMENT BROUGHT ABOUT TO THE FILTERING EFFICIENCY OF DUST SEPARATORS BY PRECHARGING.THE THEORETICAL CALCULATIONS MADE BY THE PROPOSER SHOW THAT FOR A POLARIZED PEBBLE BED WITH TYPICAL VALUES OF THE PARAMETERS (SUPERFICIAL GAS VELOCITY OF 0,5 M/S,BED DEPTH OF 20CM AND PEBBLE DIAMETER OF 5MM),THE FILTERING EFFICIENCY IS EXPECTED TO INCREASE FROM ABOUT 80% FOR IMPACTION ALONE TO MORE THAN 99,5% FOR THE PROPOSED SYSTEM.THIS RESULT SHOWS THAT THIS TYPE OF FILTER CAN BE VERY EFFICIENT;IF THE EXPECTED RESULTS ARE COFIRMED BY THE EXPERIMENTS, A NEW TYPE OF FILTER COULD BE PROPOSED AS CONFIRMED BY THE EXPERIMENTS,A NEW TYPE OF FILTER COULD BE PROPOSED AS A SUBSTITUTE FOR THE CONVENTIONAL ONES IN A NUMBER OF CASES WHERE THE CLASSICAL TECHNOLOGY EXPERIENCES DIFFICULTIES.

LURGI HAS A LONG INDUSTRIAL EXPERIENCE OF DUST SEPARATORS,AND COULD EXPAND THE RANGE OF ITS PRODUCTION OF INDUSTRIAL FILTERS IF THE EXPERIMENT IS SUCCESSFUL;ECOPOL IS THE MANUFACTURER OF THE INJECTORS AND WILL HAVE A LICENCE OF THE RELATED PATENTS.

THE INSTITUTE OF CHEMICAL ENGINEERING OF THE UNIVERSITY OF PADERBORN HAS GAINED FOR YEARS A DEEP EXPERIENCE IN DUST SEPARATION AND HAS THE FACILITIES AND THE BASIC EQUIPMENT FOR TESTING THE PROPOSED METHOD.
ECOPOL HAS BUILT,IN ASSOCIATION WITH ONERA,A FACILITY SPECIALIZED FOR STUDYING THE PEBBLE BEDS FROM NORMAL TEMPERATURES TO 800 C.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Ecopol SA
Address
26 Rue Du Château-des-rentiers
75013 Paris
France

Participants (2)

Lurgi Metallurgie GmbH
Germany
Address
Lurgi-allee 5
60439 Frankfurt Am Main
UNIVERSITAET - GESAMTHOCHSCHULE PADERBORN
Germany
Address
Warburger Strasse 100
33098 Paderborn