air pollution control technology in japan _full

8/6/2019 Air Pollution Control Technology in JAPAN _full

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Source: Global Environment Centre Foundation (GEC) - Ministry of the Environment of Japan - Website: http://gec.jp/

Reedited by: Environmental Industry Development., JSC No 42/117, Thai Ha str., Hanoi. 1

Exhaust Gas Treatment Equipment

PIPE FILTER (Exhaust Gas Processing Unit)

1. Purpose

Acidic and oil mist produced in various manufacturing processes are the causes of

various types of trouble. Public sentiments and lows and regulations against pollution

and environmental problems have become stricter over recent years, increasing

demands for exhaust gas treatment for factories.

The exhaust gas processing system using a pipe filter which we are now introducing

aims at processing floating mist and gases efficiently with a simple unit and with lower

maintenance and running costs.

2. Performance and Characteristics

Target exhaust gas:

Exhaust gases containing any type of mist except for strong alkali or hydrogen fluoride

Diameter of mist particles to be processed:

0.025 micro - m or over

Collecting efficiency: 95 - 100%

Pressure loss: 50 - 250 mmH2O

3. Features

The pipe filter consists of cylindrical layers of fine glass fibers would around a base

material, through which the original gases pass from the outside to the inside, and

collects mist using inertia collision, diffusion and contact.

Because the void ratio and the filtering area per filter is very large and the outer and

inner densities are diverse, all sizes of mist particles can be collected efficiently with

only a small pressure loss. Because of being made of glass, the filter is superior in

heat resistance and it does not swell nor change its shape.

The mist particles collected by the glass fiber layers are naturally coagulated to drop

and be discharged out through a drain. Even if the source gas includes insoluble

dust, those of particles diameter 1 micro-m or smaller flows with the collected fluid.

(Dust particles of 1 micro-m or larger should be processed in advance.) Such a self-

cleaning function allows stable performance for a prolonged period of time without

the need for maintenance, as well as having a simple structure; it can be installed

cheaper, it is compact, and operation and management are very easy.


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4. Applicable Gases

Mist and exhaust gases produced by various chemical devices and production

processes.

5. Example of Implementation

Treated gases:

Acid and alkali exhaust gases including fine metallic particles.

Gas volume to be processed: 15,000 m3N/h

Temperature of processed gas: 60 deg.C

The pipe filter is installed at the last process of the normal filling-layer type scrubber

to absorb gases and remove mist, resulting in a high processing efficiency. The

recirculating fluid lowers the processed gas temperature removing the smoke

generated by condensation caused by the temperature difference between the hot

exhaust gas from the exhaust pipe and the atmosphere.


Toxic substance removal technology

The flue gas treatment system of the municipal solid

waste incineration plant

1. Introduction


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In Japan, municipal solid waste (MSW) incineration has outweighed others in the

intermediate treatment system because of its capabilities to sanitate and reduce

volume of waste. However, environmental pollutants such as dust, NOx, SOx, HCl,

dioxins and heavy metals are included in the flue gas from MSW incinerators. As

awareness to environmental preservation, high efficient flue gas treatment system is

being required to reduce these pollutants. In this term, advanced flue gas treatment

system using the bag house filter, and catalytic denitrification tower etc. is shown.

2. Constitution

Fig.1 Schematic flow diagram of flue gas system

Acid gas cleaning : Slaked lime powders or slurry

Dust collector : the bag house filter

Filter : A felt filter cloth

Cleaning method : Pulse jet

Additive : Activated carbon powders, etc.

DeNOx : Catalytic denitrification tower

Dioxins : Catalytic denitrification tower or

Activated coke packed tower

3. Characteristic

(1) Dioxins can be removed at high efficiency by the bag house filter followed by the

catalytic denitrification tower or the activated coke packed tower.

(2) Dioxins and NOx can be removed simultaneously by the catalytic denitrification

tower.

(3) In order to improve dioxins and Hg removal efficiency, the additives such asactivated carbon is fed.


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(4) Dust, Heavy metals and acid gas such as HCl, HF, can be removed at high

efficiency by the bag house filter.

(5) The catalytic denitrification can be conducted effectively even at low temperature

using low temperature active catalyst which was developed.

4. Application field

Flue gas treatment of MSW and industrial waste incineration and melting furnace of

MSW incinerator ash.

5. Operation data and effect

Experimental data of flue gas treatment from existing fluidized bed incinerator of

MSW are shown below.

(1) Dioxins:


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Fig.3 Dioxins homologues and after activated coke packed tower

(2) NOx : < 50 ppm (denitrification catalyzer outlet)

Fig.4 Example of measured NOx at inlet and outlet of catalytic denitrification tower(Catalyst temperature 170 deg.C, SV 1600h

-1, NH3/NO.1.0)

(3) HCl :


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Hg < 0.02 mg/m3N (below 170 deg.C )

(the bag house filter outlet)

Fig.5 Relationship between operating temperature and removal efficiency of Pb,

Cd, Hg

(5) HF : Na2SOx + H2O

2) Dehumidification of absorbed gasses

Direct cooling by means of packed tower and cooling tower

3) Re-heating of treated gas

Prevention of white smoke through humidity control


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2. PROCESS FLOW CHART

Flow Sheet

3. FEATURES

(1) Acid gas high removal efficiency is attained thanks to combination of multistage

spray tower and packed tower.

(2) White smoke emitted from the stack is reduced greatly by dehumidification and

re-heating of the treated gas.

(3) Stable operation is ensured by automatic control of pH and salt concentration in

the waste liquid.

4. APPLICATIONS

KAWASAKI has abundant experiences in treatments of combustion exhaust gas

emitted from municipal solid waste containing much HCl as well as SOx.

1) Gas volume : Free

2) Gas temperature : 150 - 300 deg.C

3) Acid gas removal rate : HCl Less than 15 ppm

SO2 Less than 10 ppm

Fig.1. Actual data of HCl removing performance of wet-type noxious gas removing

equipment


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Desulfurization and Decyanization System (Fumaks Process

and Rhodacs Process)

1. Outline

Crude gas produced in the manufacture of coal gas (COG) contains hydrogen sulfide

and hydrogen cyanide. If it is released directly, it would contaminate air or cause

corrosion on industrial facilities. As city gas purification systems, Fumaks Process

and Rhodacs Process can remove hydrogen sulfide and hydrogen cyanide in the

crude gas efficiently and at low cost.

Solution of a small amount of picric acid in sodium carbonate solution, sodium

hydroxide solution or ammonious alkaline solution is circulated through the

desulfurizing tower, where hydrogen sulfide is absorbed. The solution then passes

through the regeneration tower, where hydrogen sulfide is oxidized by catalytic

reaction of picric acid. Sulfur is thus separated and recovered. Regenerated liquid is

recirculated to the desulfurizing tower. By means of Premix Nozzles, oxidation air

effectively contacts the liquid in compact regenerator at low air flow rate.

(Absorption-Regeneration Reaction: In case of NH3-alkaline)Absorption Reaction NH4OH + H2S -> NH4HS + H2O

Regeneration Reaction NH4HS + (1/2)O2 -> NH4OH + S


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By scrubbing crude gas containing hydrogen cyanide with sulfur suspended alkalic

solution, hydrogen cyanide is removed in the form of thiocyanate which is non-toxic.

(Main Reaction: In case of NH3-alkaline)

Reaction of Ammonium Polysulfide Production

2NH3 + H2S + xS -> (NH4)2SX+1

Reaction of Ammonium Thiocyanate Production

(NH4)2SX+1 + HCN + NH3 -> NH4SCN + (NH4)2Sx

2. Schematic Diagram

An example of the flow sheet of Fumaks, Rhodacs and Compacs processes

3. Advantages

- Desulfurization efficiency can be adjusted in the design close to 100% according to

the customer's requirement. Stable efficiency can be maintained.

- Low cost of chemicals for desulfurization

- The absorption liquid can be circulated (recycled) under ambient temperature

without pressurization

- Efficient regeneration by premix nozzles

- Small land space and low installation cost

- Sulfur recovery efficiency is as high as 70 to 80%

- Decyanization efficiency can be adjusted in the design up to 100% according to thecustomer's requirement.


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2) The heat consumption for regeneration of the absorbing liquid is appreciably

reduced by the use of a steam ejector.

3) The HiPure Process is a good choice for high purification where H2S must be

removed to 1 ppm or less, and CO2 to only a few ppm.

4) No specific anti-corrosive material in needed for the equipment.

5) The absorbing liquid is nontoxic and no proprietary chemicals are used.

6) The absorbing liquid suffers no degradation and a reclaimer is not necessary.

3. Process Flow

The absorption and regeneration of acid gases in the Benfield Process are based on

the following reactions:

K2CO3 + CO2 + H2O = 2KHCO3 (1)

K2CO3 + H2S = KHS + KHCO3 (2)

In the HiPure Process, the reactions described below are added.

2R2NH + CO2 + H2O = (R2NH2)2CO3 (3)

(R2NH2)2CO3 + CO2 + H2O = 2R2NH2HCO3 (4)

2R2NH + H2S = (R2NH2)2S (5)

(R2NH2)2S + H2S = 2R2NH2HS (6)

The absorption and regeneration of acid gases are conducted in a similar way to that

of the conventional amine or carbonate processes. The gas to be treated is fed to the

bottom of the absorber and flows countercurrent to the absorbing liquid supplied at

the top of the absorber.

Acid gases are then absorbed by the absorbing liquid. The liquid that has absorbed

the acid gases is preheated and then supplied to the top of the regenerator where the

acid gases are stripped by steam for the regeneration of the liquid. The regenerated

liquid is precooled and recirculated to the absorber.

4. Benfield Process


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Process Flow Diagram


Acid gas purification techniques for H2S (hydrogen sulfide) -

Stretford Process

1. Outline

The Stretford Process is a wet-type desulfurization process used in various industries

in which hydrogen sulfide is removed from gas streams and sulfur is recovered.

About 100 plants have been constructed worldwide and have operated successfully

since this process was developed by the British Gas Corporation. It has become one

of the most widely used desulfurization processes with an excellent performance

record.

Kobe Steel, Ltd. first obtained technical assistance from the British Gas Corporationin 1964. Since then we have designed and constructed the plants shown in the

Reference section.


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2. Features

1) This process is applicable to any gas, such as coke oven gas, natural gas, oil

refinery, gas, reformed gas, coal gas, etc.

2) The hydrogen sulfide content in the treated tail gas can be reduced to less than

0.1 ppm at atmospheric and higher pressures.

3) Sulfur is recovered with a high purity of more than 99.5 wt.%

4) Hydrogen sulfide is selectively removed from gas streams containing a high

concentration CO2 with high efficiency.

5) Simple operation and energy savings can be achieved as the absorption and

regeneration are performed at moderate temperature (30 - 40 deg.C) .

6) The chemicals used in the process are stable, nontoxic and easily treated.

7) Several effluent treatment systems have been established. So there is no problem

of secondary pollution due to the effluent.8) The absorbing solution is weakly alkaline (pH 8.5 - 9.0) and noncorrosive.

3. Reaction Mechanism

The absorption and regeneration are based on the socalled "Redox reaction" that

causes the catalyst effects of anthraquinone disulfonic acid (in short, ADA)and

vanadate in a weakly alkaline solution.

2H2S + 2Na2CO3 -> 2NaHS + 2NaHCO3 (1)

2NaHS + 4NaVO3 + 4NaHCO3 -> 2S + Na2V4O2 + 4Na2CO3 + 3H2O (2)

Na2V4O2 + 2Na2ADA + 2Na2CO3 + 3H2O ->

4NaVO3 + 2Na2ADA(Redured) + 2NaHCO3 (3)

2Na2ADA (Reduced) + O2 -> 2Na2ADA + 2H2O (4)

4. Process Flow

The gas to be treated flows countercurrent to the absorbing solution in the absorber

and H2S is removed by the reaction with the absorbing solution. The packings used

in the absorber are usually splash-type plates designed in a specific manner. The

absorbing solution is delayed at the bottom of the absorber and hydrogen sulfide in


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the solution is converted to elemental sulfur as a result of the reaction. Then the

solution is sent to the oxidizer, where a supply of air is received to regenerate the

solution completely and to float elemental sulfur in the slurry. The froth of the sulfur

slurry is concentrated by a filter or a centrifuge to form sulfur cake, which is reslurried

with water and heated to recover molten sulfur of high purity from the sulfur

separator.

On the other hand, the solution regenerated in the oxidizer is sent to the balance pit

and then pumped up to the absorber.

5. Stretford Process

Flow Diagram


KAWASAKI LIME MOVING BED HYDROGEN CHLORIDE REMOVAL SYSTEM

(KALM SYSTEM)

1. OUTLINE

This is completely dry type cross flow moving bed system which removes acid gas

constituents effectively from the combustion exhaust gas. The quick lime (calcium

oxide) filled in the moving layer removes hydrogen chloride and sulfur oxides

effectively according to the following reaction formula.

CaO + 2HCl --> CaCl2 + H2O

CaO + SOx --> CaSOx


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Fig.1. Diagram of the Device Principle

Fig.2 Schematic of KALM


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2. PROCESS FLOW CHART

CASE 1

CASE 2

3. FEATURES

(1) Because this is of completely dry type and uses no water, no white smoke is

generated and a trouble resulting from calcium ion accumulation does not occur.

(2) When installed at downstream of the dust collecting device, reaction products can

be separated from fly ashes ensuring remarkable utilization.

(3) It is possible to remove hydrogen chloride and sulfur oxides effectively.


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4. APPLICATIONS

1) Gas volume Free

2) Gas temperature 200 - 300 deg.C

3) Acid gas removal rate HCl Less than 50 ppm

(In case of MSW Incineration Plant)

SO2 Less than 10 ppm

(In case of MSW Incineration Plant)


WET TYPE HYDROGEN CHLORIDE AND SULFUR OXIDES REMOVAL

SYSTEM1. Introduction

In this system, the exhaust gas is washed by water neutralized with caustic soda

(sodium hydroxide). This system is made up of a spray tower and a filling tower. A

dehumidifying layer should be added for plume prevention. This system has a high

efficiency of removing hydrogen chloride and sulfur oxides.

The chemical reaction formulae as follow:

HCl + NaOH -> NaCl + H2O

SO2 + 2NaOH + (1/2) O2 -> Na2SO4 + H2O

2. System outline

The exhaust gas from the incineration furnace passes through a dust collector (ESP

or baghouse) where its particulate is removed. It is then fed to the spray tower

(venturi scrubber) where its temperature is lowered to a saturated level. The exhaust

gas then goes into the filling tower. The washing water is neutralized with caustic

soda at a value of pH 7 or less.


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Fig.1 shows the flowchart of the wet type hydrogen chloride and sulfur oxides

removal system.

Fig.1 Wet type hydrogen chloride and sulfur oxides removal system

3. Characteristics

The treatment allows for removing 95 to 98% of hydrogen chloride and 85 to 95% of

sulfur oxides. Water treatment process and plume preventive equipment are

necessary. The mercury elimination efficiency is 80 to 90%.

4. Capacity

This system has no limit on the treated gas volume.

5. Sphere of application

This system can be applied to any furnace exhaust gas, for example, one for

Municipal Solid Waste (MSW) incineration.

6. Actual results

Takuma has installed 30 wet type hydrogen chloride and sulfur oxides removal

systems in MSW incineration furnaces in Japan.


SEMI-DRY TYPE HYDROGEN CHLORIDE AND SULFUR OXIDES

REMOVAL SYSTEM1. Introduction


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In this system, hydrated lime (calcium hydroxide) slurry is injected into a quenching

reactor to reduce the gas temperature and to neutralize the acid gas contained in the

exhaust gas. Hydrated lime powder is injected into a dry venturi to enhance the

pollutant removal effect. A baghouse (fabric filter) is designed to allow a formation of

a thick dust cake layer on its surface. When the exhaust gas passes through the

baghouse, the unreacted hydrated lime contained in the cake layer contacts and

reacts with the acid gas in the exhaust gas, thereby improving removal effect.

The chemical reaction formulae are as follows:

2HCl + Ca(OH)2 -> CaCl2 + 2H2O

SO2 + Ca(OH)2 -> CaSO3 + H2O

CaSO3 + (l/2)O2 -> CaSO4

2. System outline

In the hydrated lime slurry tank, hydrated lime is mixed with water to form a slurry

and then fed into the quenching reactor. Hydrated lime slurry is sprayed with air by

dual fluid nozzles. Hydrated lime powder and a powder type special dose are injected

into the dry venturi by the blower. The exhaust gas containing hydrated lime powder,

special dose auxiliary and reaction products is then fed into the baghouse.

Fig.1 shows the flowchart of the semi-dry type hydrogen chloride and sulfur oxides

removal system.

Fig.1 Semi-dry type hydrogen chloride and sulfur oxides removal system

3. Characteristics


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sulfur oxides. Water treatment process and plume preventive equipment are not

required. The mercury elimination efficiency is 50 to 70%.

The removing performance of the semi-dry type is largely dependent on the gas

temperature at the baghouse; the gas temperature should be controlled veryprecisely by spraying hydrated lime slurry in the quenching reactor. At lower gas

temperatures, larger amounts of hydrogen chloride and sulfur oxides are removed.

5. Capacity




Municipal Solid Waste (MSW) incineration.7. Actual results

Takuma has installed 10 semi-dry type hydrogen chloride and sulfur oxides removal



DRY TYPE HYDROGEN CHLORIDE AND SULFUR OXIDES REMOVAL SYSTEM

1. Introduction

In this system, hydrated lime (calcium hydroxide) powder is injected into the exhaust

gas through a dry venturi to neutralize acid gases. A baghouse (fabric filter) is

designed to allow a formation of a thick dust cake layer on its surface. When the

exhaust gas passes through the baghouse, the unreacted hydrated lime contained in

the cake layer contacts and reacts with the acid gas in the exhaust gas, thereby

improving the removal effect.

The chemical reaction formulae are as follows:


SO2 + Ca(OH)2 -> CaSO3 + H2O

CaSO3 + (1/2)O2 -> CaSO4

2. System outline

Hydrated lime powder and a powder type special dose are injected into the dryventuri

by the blower. The exhaust gas containing hydrated lime powder, special dose

auxiliary and reaction products is then fed into the baghouse.


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Fig.1 shows the flowchart of the dry type hydrogen chloride and sulfur oxides removal

system.

Fig.1 Dry type hydrogen chloride and sulfur oxides removal system

3. Characteristics


sulfur oxides. Water treatment process and plume preventive equipment are not

required. The mercury elimination efficiency is 50 to 70%.

The removing performance of the dry type is largely dependent on the gas

temperature at the baghouse; the gas temperature should be controlled very

precisely by spraying water at an upstream quenching cooler. At lower gas

temperatures, large amounts of hydrogen chloride and sulfur oxides are removed.

4. Capacity




Municipal Solid Waste (MSW) incineration.

5. Actual results

Takuma has installed 15 dry type hydrogen chloride and sulfur oxides removal



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Catalytic Incinerator

1. Outline

This equipment catches malodorous gases with the platinum catalyst and

decomposes them by oxidation to harmless and odorless carbonic acid gas and

water. Compared with the direct combustion type, this equipment is capable of

treating malodorous gases at low temperature, so running cost is low. In case

concentration of malodorous substances is low in particular, it is advisable to installHoneycomb Type Deodorization Equipment as a pre-treatment equipment to save

energy greatly.

2. Structure of the equipment

- Treating gas containing malodorous substances are pre-heated while it is passing

through the heat exchanger.

- Treating gas is heated to the predesigned temperature by the auxiliary heater

(generally to 300 deg.C ). Electricity, city gas, LPG, kerosene oil, etc. can be selected

as heat source.


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- When heated treating gas passes through the catalyst-bed, malodorous substances

contained are decomposed by oxidation as they contact the catalyst.

- Purified gas is exhausted after passing through the heat exchanger where heat is

exchanged between purified gas and treating gas.

In combination with a steam heater:

In case electricity is used as heat source for the auxiliary heater, it is advisable to use

a steam heater together with it to reduce electric consumption greatly, which reduces

running cost.

3. Features

- Low running cost: Compared with the direct combustion system, this equipment is

capable of treating malodorous substance at low temperature, so fuel costs can be

reduced by under (1/3).

- No secondary air pollution is ensured.

- Low boiling organic solvents and wider ranges of malodorous substances can be

purified.

- Power source for auxiliary gas burner can be selected widely. Since the mixed type

gas burner is used, city gas, LPG, butane gas, etc. can be used as heat source with

the simple adjustment of the gas burner. Electric system is standardized for smaller

units.

4. Applied fields

Chemical industries, painting, printing, rubber and casting factories

5. Installation example of system


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DRY TYPE FLUE GAS TREATMENT SYSTEM

1. PREFACE

Millions of tons of waste are produced worldwide every day; most of it is dumped in

landfills or discharged to rivers and sea without prior treatment. However, while the

demand for waste disposal capacities is increasing, the availability of suitable sites is

on the decline. Waste has become a critical problem for industrial society, particularly

in big cities and densely areas. Therefore, the need to avoid or reduce the generation

of waste and to recycle the waste produced will become an ever important political

and economic issue. However, disposal capacities will continue to decrease in spite

of the reduction in the volumes of waste produced. For this reason it is necessary tocoordinate and optimize waste management.

The future development of incineration as a waste disposal method will of course

depend mainly on whether optimum reductions in the total emissions of solid, liquid

and gaseous products from waste incineration plants can be ensured without leaving

environmental and economic aspects unconsidered. The prevailing trend can be

clearly seen from the changes in the European and Japanese emission limits for flue

gases from waste incineration plants.

HITACHI ZOSEN has been making every effort to research, develop and improve

flue gas cleaning systems to meet clean air standards which are getting progressively


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more and more strict and severe in every countries in the world. This document

briefly introduces DRY TYPE FLUE GAS TREATMENT SYSTEM which is one of

typical types of flue gas cleaning system.

2. PROCESS DESCRIPTION

This system consists of the following equipment as shown on fig.1;

- Evaporative Type Cooler

- Bag Filter

- Storage and injection equipment for Lime and Supplemental agent

Fig.1 DRY TYPE FLUE GAS TREATMENT PROCESS

(Waste Heat Boiler Type Cooler)

Fig.1 is simplified flow chart of this DRY TYPE FLUE GAS TREATMENT SYSTEM

(Bag filter system). Flue gas from a refuse incinerator is fed to Evaporative Type

Cooler, in which the flue gas temperature is regulated by means of evaporation of

injected water. The flue gas temperature at the inlet of Bag Filter is controlled to be

appropriate for the reaction, which makes the removal of gaseous pollutants efficient

and prevents the filter cloth from clogging caused by melting of reaction products

(salt) such as CaCl2 and suffering heat damage.

After being temperature-conditioned, the flue gas is mixed with fine-grained Ca(OH)2

and supplemental agent which are supplied into the flue gas duct, where powdered

Ca(OH)2 reacts with gaseous pollutants such as SO2, SO3, HCl and HF (if any). In

simple terms, the following reactions take place;

2SO2 + 2Ca(OH)2 -> 2CaSO3.(1/2)H2O + H2O (1)


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SO3 + Ca(OH)2 -> CaSO4.2H2O (2)

2HCl + Ca(OH)2 -> CaCl2 + 2H2O (3)

If HF is present in the flue gas,

2HF + Ca(OH)2-> CaF2 + 2H2O (4)

The powdered Ca(OH)2 reacts with the gaseous pollutants on its surface and core of

particle remains unused. The gas/solid mixture is fed into the Bag Filter, in which

solids (reaction product, unused Ca(OH)2 and flue gas dust) are effectively separated

from the flue gas through the filter cloth. The gaseous pollutants will come in contact

with unused Ca(OH)2 for further reaction.

The filtrate cake is periodically removed from the filter cloth by means of pulse jet of

compressed air injected into clean side of the bag house with a lance(on-line

cleaning).

Supplemental agent is added to the powdered Ca(OH)2 to facilitate the removal of

the cake and the above mentioned reaction, furthermore in case of special

supplemental agent supplying, it effects removal of another pollutants which are

Dioxins and Hg, due to carbon contained in the supplemental agent.

The relation between the flue gas temperature controlled, Equivalent of Ca(OH)2 to

HCl/SOx and the gaseous pollutants removal efficiency is shown on fig.2.

Fig.2 HCl and SO2 removal efficiency on a bag filter system


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3. SYSTEM FEATURES

Nowadays this system has high performance of noxious gases removal at the same

as with the Wet Type Process on constant research and much experience on this

system (We at HITACHI ZOSEN has 44 plants of actual experience as of April,

1998).

This DRY TYPE FLUE GAS TREATMENT SYSTEM has main features as follows;

- High removal efficiency for noxious acid gases

- Simple and easy maintenance

- Stable and easy operation

- Low capital costs


WET TYPE FLUE GAS TREATMENT SYSTEM

1. PREFACE

HITACHI ZOSEN has been making every effort to research, develop and improve

flue gas cleaning systems to meet clean air standards which are getting progressively

more and more strict and severe in every countries in the world.

This document briefly introduces WET TYPE FLUE GAS TREATMENT SYSTEMwhich is one of typical types of flue gas cleaning system.


This system consists of the following equipment as typically shown on fig.1;

- Scrubber and Water circulation pumps

- Hydrocyclone and Effluent Pump

- Cooling Tower and Gas Reheater

- Caustic soda storage and injection equipment


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Fig. 1 WET TYPE FLUE GAS TREATMENT PROCESS

This process can be subdivided into the following steps;

(1) Flue gas cooling and scrubbing

Flue gas from a refuse incinerator is fed to Scrubber in which the flue gas is cooled to

saturation temperature and simultaneously contained gaseous noxious pollutants are

absorbed (removed) by contact with circulating water. The noxious pollutants

absorbed in the circulating water, reacts with caustic soda injected as follows;

SO2 + 2NaOH -> Na2SO3 + H2O (1)

SO3 + 2NaOH -> Na2SO4 + H2O (2)

HCl + NaOH -> NaCl + H2O (3)

If HF is present in the flue gas,

HF + NaOH -> NaF + H2O (4)

(2) Absorbing and dehumidifying

The flue gas from the lower part (Cooling Part) rises to the upper part(Dehumidification Part) of the Scrubber, where the gas is first distributed to the

packed bed and contact with circulating water efficiently for further absorption of

remained gaseous pollutants. Simultaneously the flue gas is supercooled

(dehumidified), because the circulating water is forced to be cooled through Cooling

Tower, and it effects prevention of white plume from the Stack.

(3) Hot air mixing and Treated flue gas reheating

The flue gas leaving this Scrubber is fed into Air/Gas Mixer where the flue gas ismixed with heated air, thus the flue gas is heated up and its water content is reduced

to be under less than saturation point. After that the flue gas is fed into Gas Reheater


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where it is heated up again to a temperature above 140 deg.C that is minimum

temperature for preventing corrosion trouble of the following metal-made equipment.

The condition of flue gas introduced to the Stack; its water content and temperature,

is settled for prevention not only of above mentioned corrosion trouble but also of

white plume exhausting from the stack.

(4) TDS concentration control of the circulating water

As is mentioned above, acid gas such as HCl and SOx contained in the flue gas is

neutralized with caustic soda injected into the circulating water, and as a result it

generate salt such as NaCl and Na2SO4. If this salt was not at all discharged, it is

possible to cause clogging of the flue gas entrance of the Scrubber by its drying-up

(Crystallising). Therefore, a part of the scrubbing water is withdrawn from the

Scrubber sump with adjusting concentration of salt-compounds (TDS) not more than

10% and is sent to Wastewater Treatment Plant. The Scrubber sump bottom is

withdrawn periodically and pumped up to Hydrocyclone in order to remove solids or

foreign materials which might cause clogging of Spray Nozzles for the circulating

water.

3. SYSTEM FEATURES

Flue gas introduced into Scrubber is very corrosive due to contained various acid

gases, and has a high temperature, therefore it is necessary for the Scrubber to be

specially considered to be protected from troubles such as its internal's corrosion and

burning out. The inside of this Scrubber is made completely corrosion-proof and

thermal resistant by employing firebricks, resin and resin lined material. And further

other assistant equipment is designed for keeping not only of its performance, but

also its stable operation, on our much experience on this system (We at HITACHI

ZONES has 29 plants of actual experience as of April, 1998). Thus this our WET

TYPE FLUE GAS TREATMENT SYSTEM has main features as follows:

- High efficiency of noxious pollutants removal

- Simple structure free from corrosion- Stable and easy operation

- Very low pressure loss (This means economical)


EDV TYPE FLUE GAS TREATMENT SYSTEM

1. PREFACE

HITACHI ZOSEN has developed various kinds of innovative or improved

technologies in the field of environmental protection processes since we first


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constructed a refuse incineration plant in 1964. In 1988, we introduced a new

technology from LAB. S. A. in France, which treats dedusting and toxic gas

absorption simultaneously. This technology is called Electrodynamic Venturi (EDV)

Process.


This process consists of the following units;

(1) Dedusting unit

Flue gas is fed to the top of Dedusting Column from a refuse incinerator, where the

flue gas is quickly cooled down and comparatively large particles of dust and

gaseous pollutants such as HCl and HF are removed by contact with circulating

water sprayed by LAB-G nozzles. Effluent from the bottom of this Dedusting Columnis circulated to the top of this Column by a water circulation pump. A part of

circulating water is withdrawn and is fed back after sludge removing via Hydrocyclone

and Thickener, and the wastewater contains the sludge is sent to Wastewater

Treatment System. This circulating water is injected with hydrated lime milk as an

absorbent and thus its pH value is controlled to be 1.5 - 2.5.

(2) Venturi dust collector unit

From the Dedusting Column, the flue gas is introduced to Venturi-type Dust Collector.

In this equipment, small particles of dust and water mist which is unable to be

removed in previous dedusting, are removed. At both inlet and outlet of this Venturi-

type Dust Collector, LAB-F nozzle is equipped which were developed by LAB.S.A.

The dust is covered by condensate through adiabatic expansion and collected by

sprayed water which is circulated via Circulation Tanks installed at inlet and outlet of

this Venturi-type Dust Collector respectively.

(3) Absorber unit

From the Venturi-type Dust Collector, the flue gas is fed to lower part of Absorber

where gaseous sulphur oxides are removed by contact with circulating water sprayed

through LAB-G nozzles. And here the gas can be dehumidified simultaneously, if the

circulating water is cooled through a cooling tower. It is effective to prevent white

plume exhausting from the Stack.

(4) Electrofiltering module unit

Flue gas saturated with water from the Absorber is introduced to the following

Electrofiltering module via Mist separator where entrained mist is removed. The

Electrofiltering module is one of venturi and it removes very small particles of micron


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size(organic and inorganic chlorine compounds, heavy metals, etc.) which are

contained in the flue gas. The small particles are collected by the filtered water film

by means of electromagnetism.

(5) Chemical dosing unit

Hydrated lime is supplied in powdered form to Lime Silo by lorries. This hydrated lime

is fed to a desolving tank where it is adjusted as slurry of concentration of approx. 5 -

10%, and after that it is injected into circulating water of the Dedusting Column.

Further caustic soda of approx. 10% concentration is injected into circulating water of

the Absorber.

3. SYSTEM FEATURES

This process has the following advantages;

(1) Compact, simple and small space required

This process has two functions, that is, dust collection and absorption of gaseous

pollutants such as HCl, SOx, HF. This process is compact and simple compared with

one which treats functions separately.

(2) LAB-G nozzle for slurry

LAB-G nozzle developed by LAB. S. A. has an original structure which is suitable for

a high density slurry with less blockage, erosion and damage.

(3) Low chemical cost

This process uses hydrated lime or limestone as an absorbent. The chemical cost is

very low, approximately one third that of the conventional process, which uses

caustic soda.

(4) High small-particulate collection efficiency

This process effectively collects small particulates of micron size including organic or

inorganic chlorine compounds and heavy metals in the last unit, i.e., Electrofiltering

modules.

(5) No heavy metal in the effluent

This process does not discharge any metals in the effluent and so it will be suitable

for the stricter effluent limits of the near future.

We are very glad if this EDV TYPE FLUE GAS TREATMENT SYSTEM would be of

service for worldwide clean air protection.


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Fig.l EDV PROCESS


NIPPON SHOKUBAI'S Catalytic Incineration System

1. Principle of Catalytic Incineration System

The catalytic incineration method is to convert exhaust-gases into harmless and

odorless by complete catalytic oxidation.

Basic reaction scheme is expressed as follows;

CmHn + O2 -> CO2 + H2O + Reaction Heat

On the contrary, in the direct incineration system, exhaust-gases are burnt up in

direct contact with a burner flame at higher temperatures of 700~900 deg.C. If a

catalyst is used in this process, its excellent catalytic performance will bring about thesame effect with that of the direct system at far lower temperatures of 200 ~ 400

deg.C.


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2. Basic System

The exhaust-gas containing organic compounds is sucked into the heat exchanger

for preheating, and further heated in the gas heater before entering into the reactor.

After the exhaust-gas is decomposed and purified by the catalyst in the reactor,

treated gas is recycled into the heat exchanger to recover the reaction heat and

finally discharged from the stack into the atmosphere.

Depending on the contents and other conditions of exhaust-gas and the design of

heat exchanger, the system provides an energy-saving operation which decreases or

does not require auxiliary fuels.

3. Excellent Features of Catalytic Incineration System for Exhaust-Gas

Treatment

Among NIPPON SHOKUBAI's waste gas control systems, the catalytic incineration

system employing catalyst of NIPPON SHOKUBAI's own development provides

complete oxidation of pollutants and odorous substances at low temperatures

converting them harmless and odorless.

It has many excellent features as anti-pollution and energy-saving equipment.

- Most suitable design

- Low Running Cost

- Perfect Treatment- Easy Operation

4. Wide Range of Applications

Application

- Paint and Ink Manufacturing

- Solvent, Adhesives and Synthetic Resin Manufacturing

- Chemical Manufacturing

- Food Manufacturing

- Industrial Wastes Handling- Odor Substances Handling etc.


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An Organic Halogen-Gas Purification System:

The "HALOCAT" Catalytic-Incineration Exhaust-Gas

Treatment Apparatus

1. Introduction

This exhaust gas treatment system provides the effective purification of the organic

exhaust gas containing halogenated organic compounds by employing catalysts of

Nippon Shokubai's own developed (STH-catalyst).

Organic exhaust gas containing halogenated organic compounds can be

decomposed by catalytic incineration and is converted into CO2, H2O and hydrogen

halogenide.

Then the hydrogen halogenide is neutralized by alkalied solution in the scrubber.

Therefore the above-mentioned exhaust gas can be purified without generating

hazardous exhaust gas and waste water.

2. Outline of this system


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3. Excellent feature of this system

1) Organic exhaust gas even containing halogenated organic compounds can be

converted effectively into harmless substance.

2) Low running cost.

3) Purification of various kinds of halogenated organic compounds at low

temperature.

4) No hazardous waste water is generated.5) No hazardous by-product such as CO and halogen gas is generated.

6) As the catalyst is a honeycomb form, the pressure drop thereof is low.

7) A catalyst to be used keeps its stable effect for a long span of life-time.

8) Easy operation (can be operated with an automatic control requiring no

manpower) and easy maintenance.

4. Purification efficiency of chlorinated organic compounds


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THE FLUE GAS TREATMENT SYSTEM OF THE MUNICIPAL SOLID WASTE

INCINERATION PLANT

1. Introduction

The exhaust gas generated from the incineration of municipal solid waste contains

harmful substances that cause air pollution, such as dust, acid gases (SOx, HCl, NOx)

and heavy metal particles (Pb, Zn, Cu, etc.).

This device removes wide range of these harmful substances with high efficiency.

2. Process outline

The exhaust gas from the municipal solid waste incinerator is cooled to a

temperature of 180 to 200 deg. C by the gas cooler, and then enters the mixing

chamber located at the inlet of the bag filter.


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Filtration agency and hydrated lime transported by air from those silos are injected

into the mixing chamber. When mixed with the exhaust gas, the hydrated lime reacts

with hydrogen chloride and sulphur oxides, forming solid matter, which is collected by

the bag filter.

These chemical reactions are as follows:


SOx + Ca(OH)2 -> CaSOx + H2O

The surface of the bag filter is also coated with filtration agency and hydrated lime,

and this coating effectively collects dust and heavy metal particles.

Fig. 1 shows the flowchart of exhaust gas treatment system.

Fig. 1 Flowchart of exhaust gas treatment system.

3. Process features

1) The device uses dry-type processing which does not affect the exhaust gas

temperature directly. Therefore, no corrosion or dust adhesion trouble occurs in the

equipment.

2) The filtering effect of the filtration agency and hydrated lime prevents clogging of

the filter cloth, providing stable plant operation without an increase in the filtering

pressure loss.

3) The filtering effect of the filtration agency and hydrated lime removes dust and

microscopic heavy metal particles effectively.

4. Processing capacity

1) Gas volume : no limitation2) Gas temperature :160 to 220 deg.C


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5. Application range

This device is designed mainly for the treatment of exhaust gas generated by the

incineration of municipal solid waste. However, it can also be used to process gases

produced from various types of furnace.

6. Performance measurement result

Table 1 shows an example of performance measurement.

Table 1 Example of performance measurement


NKK LIMAR - Bag System (Dry type)

1. Introduction

The system is used for removing hydrogen chloride (HCl) and sulfur oxides (SOx)

contained in the flue gas. Slaked lime in the powder form is injected into the flue gas

to cause contact reaction with HCl and SOx. The system is further provided with bag

filters. As the flue gas passes through the dust layers created on the surface of bag

filter cloth, unreacted slaked lime reacts with HCl and SOx contained in the flue gas,

resulting in a very high removal rate.

The reaction formula is given below.

Ca(OH)2 + 2HCl -> CaCl2 + 2H2O

2. Process Flow


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Since slaked lime is injected in the powder form, the system simple.

According to the flow described above, HCl can be removed as low as 40 ppm (in

terms of 12% O2), but when removing HCl to less than 40 to 25 ppm (in terms of 12%

O2), reaction assistant agent has to be injected together with slaked lime as shown in

the figure below:

3. Characteristics

(1) Equipment is simplified.

(2) Lowering the inlet flue gas temperature of bag filter permits higher removal

efficiency. However, when the temperature drops below 140 degrees C, low

temperature corrosion is generated in the ducts and casing. Therefore, the system

should be operated at temperatures above 150 degrees C to prevent the corrosion.

(3) The reaction assistant agent which would be injected in order to raise the reaction

efficiency, is an extremely porous particles so as to promote the depositing of

reaction products on the bug filter cloth dust layers. This arrangement also promotes

better permeability and it also aids in increasing the chances of contacting unreactedslaked lime contained in the reaction products.


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Relation between reaction temperature, Ca(OH)2 ratio and HCl removal efficiency

4. Results


NKK LIMAR-Bag System (Semi-Dry Type)1. Introduction

The system is used for removing hydrogen chloride gas (HCl) and sulfur oxides (SOx)

from flue gas to a low concentration of 20 ppm, respectively (in terms of 12% O2).

Slaked lime is dissolved in water, and the slurry is refined with an atomizer for

injecting into flue gas. HCl and SOx contained in the flue gas are dissolved in droplets

containing slaked lime, reacts with slaked lime in the droplet, forms calcium chloride

(CaCl2), and stabilizes as solid salt. In the next instance, solid salt is completely dried

and formed into a spherical porous reaction products. The unreacted slaked lime


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proceeds to slowly react with HCl and SOx contained into the flue gas. This reaction

occurs at bag filters.

The reaction process is shown in the figure below. Electronic microscopic photos of

reaction products are also shown below.

Reaction Process

2. Process Flow


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Slaked lime is atomized into flue gas by dissolving it in water and forming a slurry.

3. Characteristics

(1) Since the system uses low cost slake lime and high reaction efficiency, the

operating cost is low.

(2) Since secondary reaction is present by the use of bag house, a very high

removal efficiency is obtained. This is made possible by the porous particles of

reaction products captured at the bag filter. As the flue gas slowly passes through the

reaction product particles and the dust layers on the bag filter cloth, the chances of

unreacted slake lime reacting with HCl and SOx are increased.

4. Removal Efficiency

HCl removal efficiency


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Example of measurement


ABB FILSORPTION SYSTEM for controlling toxic elements in

flue gas

1. ABB Filsorption System

ABB Filsorption System stands for simultaneous Filtration and Sorption of flue gasesand their contaminants by means of a ABB Fabric Filter acting as both filter and

chemical reactor. The system can for example be installed after wet scrubbers in

Waste to Energy plants for the final removal of dioxins and heavy metals. It also acts

as a polishing filter for dust and acidic gases. The ABB technique with injection of a

mixture of lime and activated coke or carbon upstream of the fabric filter for

absorption of these contaminants is a safe and proven technology which gives

extremely low emission levels.

ABB pioneered the Filsorption technology and has now more than 15 years

comprehensive operating experience from extremely tough and demanding

applications. ABB has also developed the technique of feeding, conveying, collecting

and handling the Filsorption product to an impressive level of reliability.

With plants in commercial operation for more than one decade, ABB has gained

extensive experience from installing Filsorption Systems. Over 90 fabric filter

installations in Waste to Energy plants clean safely and effectively more than

11,000,000 m3 of flue gas every hour.


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Pollutants in flue gases

2. The fabric filterThe fabric filter used in this application is the wellproven Optipulse filter. This

application has a uniform sorbent distribution over the bags, producing a constantly

low dust emission. In the Filsorption System the fabric filter acts as a fixed-bed

reactor where the flue gases pass the absorbent layer formed on the bags.

The filter bags are cleaned by means of compressed air pulses which are directed

down through the bag openings. The compressed air expands the bag with a

stepped acceleration so that a fraction of the dust on the outside of the bag is

detached in a carefully controlled manner.

3. The technology

Activated coke or carbon with its high surface area is known to be effective in

collecting high molecular weight organic and mercury compounds. In the Filsorption

System a mixture of lime and activated coke or carbon is carefully distributed in the

gas stream by means of ABB compact reactor. The even distribution over the filter

area provides extensive contact between gas and sorbent, which is a prerequisite for

efficient cleaning. The lime enables the removal of acidic gases such as HCl, SO2

and SO3 in addition to the removal of mercury and organics by the coke/carbon.

The excellent collection characteristics of the fabric filter ensures extremely low

particulate emission levels.

The end product from the Filsorption System is normally fired in the waste furnace

where the lime acts as an absorbent contributing to a pre-separation of acidic gases

from the flue gas. Other methods are glassification or for neutralization of waste

water.


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The Filsorption system - reactor and filter - is designed with vertical or very steep

walls in the ducts and hoppers, making the dust discharge very effective.

Consequently all problems with dust deposits and sticking dust are eliminated.

4. Performance

By using the ABB Fabric Filter as a fixed bed absorption reactor the total particulateemission is kept extremely low. This also allows the use of a fine-grained coke or

carbon while still maintaining a very low dust emission. The fine-grained coke or

carbon creates a very large contact area with excellent absorption for a given amount

of coke or carbon.

The ABB Fabric Filter offers an optimal collection capacity of sob-micron particles

thereby ensuring very low emission levels of heavy metals.

The even distribution of sorbent over the bag surface is an inherent feature of theABB design - a small deficit of sorbent anywhere on the surface will decrease local

flow resistance. This in turn leads to increased gas flow and due to the continuous

feed of sorbent, to immediate local cake repair. In this respect, the system is self-

balancing and automatically assures optimum sorbent/dust cake contact with the flue

gases.

Results from Installation


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Waste Ozone Decomposition System

This system efficiently decomposes ozone in the waste gas with the catalyst

composed of metallic oxide. The catalyst is wear resistant and free from hazards ofcombustion and explosion. As the ozone decomposing reaction using the catalyst is

performed even at low temperatures, the system can decompose the waste ozone

(low to high concentration) for a long time at low cost.

1. Features

1) Compact size.

2) Low and economical running cost.

3) Simple operation and easy maintenance.

4) Long catalyst life.

5) Excellent ozone decomposing complying with low concentration.

6) A large opening ratio and low pressure drop due to honeycomb structure.

2. Applications

Air cleaner (room, car and garbage deodorization)

Ozonizer Ozone sterilizer

High-concentration ozone treatment Semiconductor manufacturing process Water

supply and sewage water treatment Other fields requiring waste ozone treatment

3. System Flow


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Quench tower

The Quench tower is designed and engineered for cooling high temperature exhaust

gases from incinerator, melting furnace, drying furnace, etc.

Exhaust gas from high temperature sources is cooled down with water vapor to the

saturation temperature of the gas by Quench tower. The Quench tower is used as a

pre-cooler for scrubbers, electoststic precipitators, etc.

Technical Information

Specification :

The Quench including spray headers and spray nozzles are made of corrosion

resistant materials, such as lining carbon steel, type 316L stainless steel, Hastily-C.

Uniform water spraying is made by special spray nozzles.

Both horizontal flow type and vertical flow type are available.

Advantages :

- No dioxins is generated in the Quench tower.

- The Quench tower can be as a simple scrubber.

- For corrosion resistance, lining type and wetted surface type are available.

air pollution control technology in japan _full

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