I. General
Kimre`s Aerosep system is a fully-developed multiple stage aerosol separation system. This proven air pollution control technology eliminates liquid and solid particles as small as 0.2 micron in diameter. AEROSEP systems are used for emission control in areas such as flue gas clean-up in municipal solid and hazardous waste burning, and coal-fired power generation and particle removal in the fertilizer and semiconductor industries.
AEROSEP aerosol separation systems can be designed for zero liquid discharge. Kimre engineers have accomplished this by controlling the heat and mass balances. They have designed this into the system taking into account the incoming process stream and the desired exit conditions.
Using AEROSEP systems, engineers are setting new performance standards for emission control. The first AEROSEP system was installed in 1986 on a coal-fired power plant in Mannheim, Germany.
The AEROSEP systems utilize a stage-wise approach to separating liquid and solid aerosols. Each stage is specifically designed to target a particular particle size range and condition. Therefore, each stage can be optimized to provide maximum efficiency and pluggage resistance, while keeping pressure drop to a minimum.
II. Typical Configuration
The typical AEROSEP system has four stages:
1. Removal of incoming particles
larger than 3 microns.
2. Growth of the incoming submicron
particles to approximately 1 micron.
3. Coalescing the 1 micron particles
to a size of 10¡12 microns.
4. Final removal of re-entrained droplets
from stage 3.
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AEROSEP
Multiple Stage ¨ç
1st Process Stage (Pre-Separation)
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III. Aerosol Formation
Absorption processes can be predicted
with known methods if one knows the required phase equilibria and
the
mass transfer coefficients. A variety
of publications exist on absorption in different scrubber liquid.
A difficult problem in absorption is
aerosol formation. This phenomenon is very important in practice
but until now
found very little coverage in
the literature on absorption processes and scrubber.
Aerosols are solid or droplet fogs that
arise from various very small particles. Depending on the source
one can
divide aerosols into three kinds:
1. Condensation aerosols
arise when a gas mixture cools below the dew point.
2.
Sublimation occurs when the sublimation point of a gas mixture is
exceeded
(solid
particle).
3. Reaction
aerosols arise from a reaction between acid and basic reactants
(solid
particle fog).
Condensation aerosols are especially
likely to form in the presence if HCl and SO3. A typical reaction
aerosol is the
ammonium chloride(NH4Cl) that
arises from the reaction of HCl and NH3. Sublimation aerosols can
occur, in melting
processes for example, but for
the present work have no significant importance. In Figure 1 we
show the particle
size of ranges of several
aerosols from the different available sources.
The droplets sizes of condensation aerosols
such as hydrochloride acid or sulfuric acid fog are mainly in the
region
between 0.5 and two microns. The particle
size of reaction aerosols, for example, ammonium chloride is
considerably
smaller and can range well below 0.5 microns.
The particle size of aerosols is mainly
dependent on the specific nucleation and coalescing conditions.
For
condensation aerosols there is a functional
relationship between the droplet size and degree of supersaturation.
According to this equation the droplet
size decreases with increasing supersaturation. Aerosols also coalesce
with
increasing life span and higher
particle density to increasingly larger particles. In any case,
the time required for the
coalescing process
is in the range of minutes and hours which is not practical for
the scrubbing processes of
aerosols which
normally lie in the range of residence time on the order of one
second. The differences in the ranges
of particle size shown in Figure 1 from different authors partly
arise from the different coalescing conditions and
supersaturation conditions used in experiments.
IV. Aerosep Applications
1. Model : HE (High Efficiency)
Liquid
Gas Phase Present, Low Liquid Viscosity, (Example : Acid Fog)
2. Model : MS (Medium Efficiency)
Liquid Gas or
Liquid, gas and solid(soluble) Phase Present, Low Liquid Viscosity,
(Example : Ammonium salts
Aerosols)
3. Model : HD (Heavy Duty)
Liquid, Gas and Solid(insoluble
unreactive) Phase Present, (Example : Fly Ash)
4. Model : UD (Ultra Duty)
Liquid, Gas and Solid(insoluble
reactive precipitating) Phase Present
Large Power Plant
Mannheim, Germany
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Process
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Approximately 50% of the flue gages produced by the 475MW block 18 of the Mannheim city power plant is desulphurized using the Walther process. In this process SO2, SO3, HCl and HF are absorbed in a two-stage wash process by an NH3 solution. The partial pressure of NH3 over the NH4OH solution is high enough for the gas phase reaction between NH3 and SO3 to produce significants amounts of reaction aerosols, mainly NH4HSO3 and (NH4)2SO4. The flue gas desulphurization plant was designed and supplied by the Krupp Koppers subsidiary, Walther & Cie GmbH, in Cologne, Germany. |
| Gas volume | Approximately 265,000SCFM (450,000N§©/h) at an average temperature of 113 of (45¡É) |
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Problem
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The aerosol concentration after the second wash tower averages 0.11-0.13 gr/SCF (250-300mg/N§©), nearly 30wt.% of which was in the size range 0.1-0.4microns (impactor measurements). A considerable mount of aerosols present were shown to be NH4Cl and NH4F. Both chevron and candle mist eliminators had failed for various reasons. |
| Specification | Maximum aerosol content in the outlet stream was not to exceed 0.004gr/SCF (10mg/N§©) |
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Solution
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An aerosol removal system was developed by Kimre in conjunction with its Swiss licensee. The system was a four-stage process incorporating a first stage to remove larger droplets, followed by particle growth and agglomeration stage to grow the aerosols which are then removed in the final stage. Known as the AEROSEPTM Multi Stage Aerosol Separation system, this proprietary technology can be tailored to a wide range of aerosol removal situations. |
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Results
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Under the given process conditions the aerosol content in the flue gas outlet was reduce to below 0.004gr/SCF (10mg/N§©) at a total pressure drop of 12-14 in. (300-350mm) WC across all the stages. For the aerosol particle growth an average of 5,500 lb/hr (2500 Kg/hr) of stream and 15 gpm (3300Kg/hr) of water at 73-87 psia (5-6bar) were required. |
Removal of Phosphoric Acid Mist
| Object | Swiss Federal Ammunition Factory in CH-Altdorf Wastegas, produced by the burning of powder residues which contains P2O5 is scrubbed using a wet scrubber. |
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Problem
|
At the scrubber outlet a phosphoric acid mist is visible which can be seen over a long distance. Neither the droplet size spectrum, nor the P2O5 mist loading was known. For this reason it was decided to carry out tests using a pilot plant(300§©/hr) belonging to Kimre`s former European licensee to find the optimal composition for a unit to remove P2O5 mist. The air was to remove enough P2O5 mist to eliminate the plume opacity. |
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Concept
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The test showed that with a four-stage AEROSEP Multi Stage Aerosol Separation System the Mist could be removed so that it was no longer visible. Kimre`s former European licensee designed the plant scale unit (5,000§©/hr) based in the test results, for an aerosol size of 0.2~0.3 microns. The function of the different removal stages are: |
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Results
|
The AEROSEP Multi Stage Separation System was delivered complete with vessel.The system was taken into operation in 1991 and has, since then, been functioning without any problems. The removal efficiency is controlled visually only. The previously clearly visible P2O5 mist had been completely eliminated. |
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B-GONTM Mist Eliminators |
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Fluegas Cleaning Waste Incineration
Object
Municipal Waste Incineration Plant GRAAB in S-Gothenburg
The turnkey fluegas cleaning system for the
3 incinerator lines, each with a capacity of 100,000 t/a was
supplied
by GOETAVERKEN ENERGY SYSTEMS AB in S-40275 Gothenburg.
The GRP-scrubbers were
designed and delivered by
Telko Engineering AB in SF-00390 Helsinki.
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Problem
|
The incinerator lines were already equipped with electrostatic
precipitators to remove most of the particulate. For the fluegas
cleaning system a scrubbing system incorporating a heat recovery system
using heat pumps was specified. Kimre`s former European licensee
was to design a dust removal system in order to reach the required
15mg/N§© dust level in the outlet. The system was to be built
directly into the scrubber vessels. The following particle size distribution was
used for the design : - 33% > 2 microns - 40% < 2 microns - 20% < 1 microns - 7% <0.7 microns |
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Concept
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A two stage B-GONTM Mist Eliminator was designed to achieve the
following removal efficiency : The first stage incorporated a spray system to avoid pluggage.
The designed pressure drop was |
| Result |
The dust removal system was installed in October 1987 and operation began mid-1988. For the definite plant delivery in 1989 the following outlet values were measured : |
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Contaminant |
Inlet |
Outlet |
Guarantee |
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Dust |
ca. 100mg/N§©* |
10 mg/N§© |
20 mg/N§© |
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HCl |
up to2000mg/N§© |
0-10 mg/N§© |
30 mg/N§© |
|
HF |
ca. 5mg/N§© |
0.1-0.5 mg/N§© |
1 mg/N§© |
|
Hg |
- |
0.1 mg/N§© |
0.3 mg/N§© |
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Dioxin |
(TCDD Equiv.) |
0.1 mg/N§© |
0.2 mg/N§© |
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*after electrostatic precipiator |
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The designed pressure drop of 60-70mm WC was confirmed after a longer operation period.
B-GONTM Mist Eliminators
KON-TANETM Scrubber and Tower Packing
AEROSEPTM Multi-Stage Aerosol Separation System
DRIFTORTM Drift Eliminators
B-GONTM, KON-TANETM, AEROSEP , and DRIFTORTM are registered Trademarks
of KIMRE, INC., USA