Advanced Technology of FlueGas Desulfurization (FGD)
YOSHIO NAKAYAMA* 1
NOBUO KOJIMA* 1
TSUYOSHI OISHI* 1
SUSUMU OKINO* 2
MASAKAZU ONIDUKA* 2

Mitsubishi Heavy Industries, Ltd. (MHI) has been developing and introducing various Double-Contact-Flow Scrubbers and Jet Air Sparger as part of flue gas desulfurization technology. The double-contact-flow scrubber features(1) super-high desulfurization performance, (2) simple structure and easy maintenance, and (3) no problems of scaling; and the Jet Air Sparger is characterized by (1) high air utilization efficiency, (2) possible elimination of oxidation air blower, and (3) no rotating elements and easy maintenance. A full scale FGD model has been constructed forthe purpose of early development of next generation double-contact-flow scrubber technology, and expansion of sales
to overseas markets. In actual plants, a desulfurization rate of 99.4% has been achieved by modifying the scrubber
used in another process into a double-contact-flow scrubber.

Mist eliminator

1. Introduction

Flue gas outlet

Recently, in its efforts against global warming, MHI
has developed technology for desulfurization of flue gas
using a wet lime/limestone gypsum process as a meansof reducing sulfur dioxide (SO 2) emissions, and has applied it in the treatment of flue gas from thermal power
plants ever since 1972.
As of July 2004, a total of 167 desulfurization systems using this wet lime/limestone gypsum process
have been installed and are working both inside andoutside Japan, and MHI is leading the world in thisfield.
While the performance of desulfurization plants issteadily advancing, users are making increased demands
every year for reduction of facility cost.
Users' requests include:(1) Easy maintenance(2) Low cost(3) Energy saving
To meet these demands, MHI has developed thedouble-contact-flow scrubber and the jet air sparger.
Outlines of the double-contact-flow scrubber and jet airsparger are introduced in this paper, together with recent operation results.

Spray pipe

Flue gas inlet

Recirculation pump
Fig. 1 Counter-current type double-contact-flow scrubber

2.1 Double-contact-flow scrubber
An example of a double-contact-flow scrubber developed using original MHI technology is shown inFig. 11.

Flue gas flows in from the inlet duct. The flue gas
is purified after contact with absorbent liquid, and isdischarged out of the system by way of the mist eliminator. The absorbent liquid is sprayed upward from a
special wear-resistant nozzle installed in the bottomof the tower, and desulfurize flue gas after gas-liquidcontact.
In a conventional scrubber, the inside is filled withpackings, porous plate, multiple spray piping networkand other structures, but this scrubber is very simple instructure, having only spray pipes installed immediately
above the inlet duct. Accordingly, as compared with theconventional system, maintenance is easier, the cost islower, much energy is saved, and the size is compact.

*1 Plant and Transportation Systems Engineering & Construction Center*2 Hiroshima Research & Development Center, Technical Headquarters

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 41 No. 4 (Aug. 2004)

2. Latest technology of flue gas desulfurization

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Flue gas outlet

Absorber

Flue gasoutletHigh density liquid drops(inclusion of gas by high density
liquid drops)
Liquid column formed by uprisingliquid and falling liquid

Flue gasinlet

Upward nozzle (self-cleaning)

Air
Single header stage spray pipe
(simple and easy maintenance)

Flue gas inlet

Jet nozzle

Fig. 2 Function and "Spouted Up" condition of liquid column

Fig. 2 schematically shows the injection state of theliquid. By interaction of falling fine liquid drops anduprising liquid drops, liquid layers of high gas-liquidcontact efficiency and high density are formed, and asuper-high desulfurization performance is achieved.
The double-contact-flow scrubber has a simple structure, with only spray pipes immediately above the inlet
duct. Scaling does not occur inside the scrubber because
there is no source of scale. In addition, since upward
nozzles are used, the spray nozzles and spray pipes arealways self-cleaned by the falling slurry.

Recirculation
pump

Fig. 3 Concept of installation of jet air sparger(3) Free from scale
Scale does not form because the inside of thescrubber is simple and internal parts (such as spray
pipes and spray nozzles) are self-cleaned.
2.2 Jet Air Sparger
The oxidizer was originally developed for the purposeof saving utilities. Fig. 3 and Fig. 4 show the concept of
the water-stream oxidizer.
The oxidizer operates as follows: (1) Jet streams arecarried out using the part of the discharge liquid from ascrubber circulation pump into a scrubber tank, (2) turns
air into fine bubbles using this liquid stream, (3) enhances
air-liquid contact with slurry, and (4) achieves efficientoxidizing of absorbent liquid by small amount of air.
The jet nozzle can self-suck the air into the nozzle
by ejector effect, and an oxidation air blower can beeliminated.
The structure is simple because no rotating element
is used and only the stationary nozzles, resulting in easy
maintenance.

.

Features of double-contact-flow scrubber(1) Super-high desulfurization efficiency
Desulfurization efficiency is more than 99% because the scrubber has high gas-liquid contact
efficiency.
(2) Easy maintenance
Maintenance is easy because the scrubber has
no internal parts except for a single stage ofsprays.

Air
Features by void formation(1) Formation of fine air bubbles(2) Spontaneous intake of airSlurryliquidOrifice

Jet stream
Fig. 4 Concept of jet nozzle

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 41 No. 4 (Aug. 2004)

2.

flow scrubbers will be produced for sale on the overseas
market in a short time.

.

Features of Jet Air Sparger(1) Air utilization Efficiency is high and energy consumption is much less than with a conventionaloxidation lance with horizontal agitator.
(2) Oxidation air blower can be eliminated.
(3) No rotating element, easy maintenance.

Specifications of test plant.

2.3 Full Scale FGD model

Capacity: Equivalent to FGD for 400 MW Boiler
Gas flow rate: 1 200 000 m3 N /h (w)Inlet SO 2: Injection by SO 2 cylinder
Location: Mihara Works of MHI

Features of test plant

So far, MHI has been developing new technology forflue gas desulfurization by gradually upscaling the test
plants at the Hiroshima Research and Development Center and others, and has applied it into the commercial
plant after completion of the verification, but recently
projects are increasing overseas in the United States,
Europe and China, for example, and in order to promotesales in overseas markets, there is now an urgent demand to develop next generation double-contact-flow
scrubbers of low cost and high performance.
Accordingly, Full Scale FGD model has been built at
the Mihara Works, with the following two purposes inmind. An outline diagram of the Full Scale FGD modelis shown in Fig. 55.
(1) Quick development of new double-contact-flow scrubber technology for next generation plant(2) Promotion of sales of double-contact-flow scrubbers
to overseas markets
It is a big feature of this Full Scale FGD model thatthe desulfurization process can be tested and analyzed
for performance at nearly the same scale as an actual
plant of 400 MW.
By verification and testing in Full Scale FGD model,various tests (bench scale test, pilot test, scale-up verification test by small-size demonstration plants)
normally required in development of new technology can
all be skipped, and new technology can be realized into
practical plant in a very short time.
Henceforth, through analysis of the test results of thisFull Scale FGD model, new generation double-contact-(1) Actual scale test plant
The following items can be tested for an actual
scale test plant. Desulfurization performance canbe analyzed and confirmed.
(a) Desulfurization performance confirmation test(b) Oxidation performance confirmation test(c) Gas flow test
There are a total of 184 points of measurements,
so data can be collected at every part of the scrubber.
(2) Use of actual limestone and gypsum slurry
With its own limestone supply system and gypsum dewatering system, tests can be made using
actual limestone.

3. Recent case of installation
As an example of a flue gas desulfurization plant thatuses a double-contact-flow scrubber system, a case ofmodification of existing desulfurization plant for Unit 3boiler at Kashima-North Electric Power Corporation (operation resumed after modification to double-contact-flow
scrubber in 2003) is introduced below.
In this case, an existing Wellman-Load technology
scrubber (sulfuric acid production process) was modified
into a counter-current type scrubber using a wet lime/
limestone gypsum process.
(1) Principal modification and features(a) Modification of existing Wellman-Load technology
scrubber into double-contact-flow scrubber
Fig. 6 shows a concept diagram of the modification.
: Modified section
Double-contactflow scrubber

XRemoval ofinternal parts

Modified section

XAfter modificationSection X-X

Fig. 6 Desulfurization plant Unit 3 at Kashima-Northern ElectricPower Corporation
Wellman-load technology scrubber is modified into double-contactflow scrubber.

Fig. 5 Outline of full scale FGD model

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 41 No. 4 (Aug. 2004)

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Fig. 7 shows the appearance of the plant.
After removal of internal parts from the existing
scrubber, the new system of spray pipes and spraynozzles was installed, and the scrubber vessel wasleft as it was, and the inside was remodeled as a
double-contact-flow scrubber.
(b) Installation of Jet Air Sparger
A Jet Air Sparger was used in the oxidation system, and the need for an oxidation air blower waseliminated.
(c) Features of modification
The existing scrubber vessel structure was utilized as far as possible, and so the construction time
was shortened, and expenses were saved as compared with the cost of new construction.
By the use of the double-contact-flow scrubber andthe jet air sparger, energy saving and low maintenance costs have been achieved, as compared withthe existing Wellman-load technology scrubber.
(2) Plant specifications after modification
Specifications after modification are as follows.
Type: Counter-current type
double-contact-flow scrubber
Flue gas rate: 579 000 m3 N /h (w)Scrubber dimensions:
9 000 (W) X 13 000 (L) X 3 500 (H)Internal scrubber section:
9 000 (W) X 5 400 (L)Oxidation system: Jet Air Sparger
Desulfurization efficiency:
Design 98%
Actual 99.4% (in performance test)

Yoshio Nakayama

Fig. 7 Outline of desulfurization plant Unit 3 at Kashima-North
Electric Power Corporation

4. Conclusions
The double-contact-flow scrubber features:Super-high desulfurization rate
Easy maintenanceNo scaling
Further improvements are planned demonstrating by
Full Scale FGD Model by utilizing the latest desulfurization technology in order to contribute to global
atmospheric protection.
Reference(1) Ukawa et al., Development of Double-Contact-Flow Scrubber
for Flue Gas Desulfurization, Mitsubishi Heavy Industries
Technical Review Vol.33 No.2 (1996)

Nobuo Kojima

Tsuyoshi Oishi

Susumu Okino

Masakazu Oniduka

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 41 No. 4 (Aug. 2004)

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