MU Scrubber

MU Scrubber is a static mixer with a mixing wing “MU Mixing Element” for stirring, which has a high performance gas-liquid contact efficiency built into a cylindrical column body. The MU Mixing Element is a spiral wing with right or left twist. Exhaust gases containing fine particles and chemicals are supplied from the top of MU Scrubber.

On the other hand, the cleaning fluid supplied from a lower tank of the equipment by a pump is injected inside a tower through spray nozzles installed in spray pipes on the side of tower’s body. While absorbing the chemical substances and dust contained in exhaust gas, this cleaning solution drops from the upper part of the tower to the lower part, collects in the downstream tank, and circulates into the tower again. In other words, while exhaust gas passing through the column and circulating liquid are flowing in parallel through MU Mixing Element installed in the column, gas and liquid are completely mixed and contacted by repeating the division, merging, shearing and spiral rotation in the right and left directions.

First, the effect of this method is to capture substances contained in exhaust gas. As described above, it increases the gas-liquid contact efficiency to achieve high-efficiency capture. The chemical substances in the exhaust gas are chemically absorbed, and the inert substances are physically dissolved and absorbed in the cleaning solution. In addition, fine particles of dust in exhaust gas grow and coarsened by agglomeration and swelling during the flowing through the equipment. In addition, it is trapped by fine bubbles generated in the column due to strong mixing of gas and liquid. Therefore, fine particles can be easily captured by the cleaning solution and suspended in the cleaning solution. As a result, exhaust gas is purified.

The second is to trap substances from exhaust gases without clogging the equipment. This is due to the interaction between the gas-liquid mixed flow of exhaust gas and cleaning fluid, and MU Mixing Element. Clogging of pores on the front and back surfaces of wings due to adhesion growth of reaction products and dust, etc. and the growth on the wall of the equipment are prevented.

The third is the reduction of pressure loss during the flowing at the treatment of exhaust gas. This is the effect of reducing pressure loss based on the structure of MU Mixing Element. In addition, the discharge of circulating cleaning fluid from the spray nozzle of the spray pipe inside the body of the tower creates an ejector effect, contributing to further reduction of pressure loss.

In this exhaust gas treatment process, new liquid is supplied to MU Scrubber as appropriate. This is to control the gas-liquid temperature, and cooling is usually performed using the sensible heat and evaporation heat of the new liquid. In addition, a heat exchanger can be installed in the circulating fluid line to cool or heat the circulating fluid from the outside. Another purpose of introducing new liquid is to control the concentration of captured substances in the circulating effluent in a tank, and to discharge the effluent containing the captured substances while maintaining the level of the tank.

As shown in Fig. 1, spiral wings with right-twist (right turn) and left-twist (left turn) are installed on the inner circumferential surface of the column, and several right-twist/left-twist wings are alternately arranged through the space. The wing has a large number of pores. The exhaust gas and the cleaning fluid flow in parallel, and while these flows through wings twisted to the right spirally, the gas-liquid mixed contact is made by dividing, merging, and shearing action in the horizontal and vertical directions. Then, they meet in a void part. Next, they are mixed and contacted by subdividing and shearing action by wings twisted to the left spirally. In this way, gas and liquid are in complete mixed contact while continuously repeating the multiple division, swirl, confluence, inversion, and radial and axial shear actions.

There are two points to obtain good gas-liquid mixing and contact conditions using MU Scrubber.

1. Increase the liquid to gas ratio (Gas flow rate is constant)
2.  Increase gas flow rate (The liquid/gas ratio is constant)

To confirm these two points, we placed a small MU Mixing Element in a tube with an inner diameter of 72 mm as shown in Fig. 2, and conducted a test in which water flows from the top to the bottom and air at room temperature flows in parallel with water. The transparent tube portion in Figure 3 is a cavity in a space part between two MU Mixing Elements. It allows the visual observation of the mixture of air and water and shows the test results under several conditions. First, the water/air ratio was changed to 8-70 l/m3 at air velocity of 10 m/sec. At this time, if the water/air ratio drops to 8 l/m3, it is poorly mixed (Photo (d)), but if the range is 15-70 l/m3 (Photos (a) – (c)), it is well mixed.

The air flow rate was then halved to 5 m/sec. Under this condition, the mixing condition with water/air ratio of 15 l/m3 was poor (Photo(e)). On the other hand, under the condition of flow velocity of 10 m/sec, the mixing was in a good status as shown in the photo © even with the same water/air ratio of 15 l/m3. This shows that faster flow rates result in better mixing. Under this condition, the mixing condition with water/air ratio of 15 l/m3 was poor (Photo(e)). Even at a flow rate of 5 m/sec, which is half of 10 m/sec, the mixture was again better when the water/air ratio was increased to 35 l/m3 (Photo(f)). Based on these tests, it was observed that the mixing state of gas and liquid was good when the liquid-gas ratio and the gas flow rate increased, respectively, and deteriorated in the opposite case.

Fig 3. Photo of Gas-Liquid Mixed Status

Photo (a)	Photo (b)	Photo (c)
Flowing amount per unit area:3,500m3/m2h	Flowing amount per unit area:3,500m3/m2h	Flowing amount per unit area:3,500m3/m2h
Gas Velocity: 10m/sec	Gas Velocity: 10m/sec	Gas Velocity: 10m/sec
Liquid/Gas ratio:70ℓ/m3	Liquid/Gas ratio:45ℓ/m3	Liquid/Gas ratio:15ℓ/m3
Photo (d)	Photo (e)	Photo (f)
Flowing amount per unit area:3,500m3/m2h	Flowing amount per unit area:1,800m3/m2h	Flowing amount per unit area:1,800m3/m2h
Gas Velocity:10m/sec	Gas Velocity:5 m/sec	Gas Velocity:5m/sec
Liquid/Gas ratio:8ℓ/m3	Liquid/Gas ratio:35ℓ/m3	Liquid/Gas ratio:15ℓ/m3

 (* Liquid-gas ratio = Amount of liquid (l/h)/Amount of gas (m3/h))

The MU Scrubber is used for cleaning exhaust gas and recovering chemical substances from exhaust gas. Its applications are as follows.

1. Treatment of exhaust gas containing HCl, Cl2, HF, SOX, NH3, NOX, Hg, DXN’s, etc.
2. Exhaust gas treatment for forming metal oxide solid by contact of water with silicon tetrachloride, silicon trichloride, silicon dichloride, silicon fluoride, titanium tetrachloride or the like
3. Dust removal of metal oxides such as SiO2 and ZnO in exhaust gas
4. Deodorization by absorption of trace malodorous components such as ammonia, triethylamine and hydrogen sulfide
5. Sterilization and sterilization of organisms such as bacteria and viruses in exhaust gas by ozone gas, etc.
6. Recovery of chemicals such as NH3 and HCl from exhaust gas
7. Dust removal and recovery of chemical substances

The following chapter shows five installation examples.

The following design conditions must be disclosed when making inquiries to MU Scrubber. The purpose is to examine the process and equipment specifications after determining the suitability of the application of MU Scrubber. The following shows almost full design conditions. We would like to receive your conditions based on the required accuracy of examination.

1. 1. 1. Treated flow: () Nm3/h
      2. Gas temperature: Operation () ° C, Design () ° C
      3. Gas source pressure: Operation () kPaG, Design () kPaG
      4. Pressure at the inlet of equipment: Operation () kPaG, Design () kPaG
      5. Distinction between components contained in exhaust gas and gases, liquids and solids: Regarding contained components a., b., c ………
      6. Distinction between components contained in exhaust gas and gases, liquids and solids: Regarding contained components a., b., c ………
      7. Concentration of components after treatment: Components a., b., c ……… are expressed in clear units such as ppm by volume and mg/Nm3.
      8. Maximum allowable pressure loss: Operation () kPa, Design () kPa
      9. Location: Exterior or Interior
      10. Footprint: Width, Depth, Height
      11. Explosion-proof measures: Required or Not required
      12. Power supply: Voltage, etc.
      13. Materials: Designated or Not designated In the case of designation, specify the material, such as PVC, FRP, SUS, titanium, etc., for the following parts as shown below. Body of the column, mixing element, circulating fluid tank, liquid piping, gas piping, circulating fluid pump, air exhauster, flange, gasket, bolt and nut, frame and basement
   1. Spare parts: mixing elements, spray nozzles, gaskets, bolts and nuts
   2. Operation Status: operation hour (hr/day), Batch/Continuous
   3. Supply of fresh liquid: name of substance, temperature, pressure, dissolved substance concentration, pH, specific gravity, viscosity
   4. Discharge fluid: name of substance, temperature, concentration of dissolved substance
   5. Use of existing information: disclosure of flow sheets for existing facilities, problems with existing facilities, and test data
   6. Utility conditions: disclosure of utility information required for exhaust gas treatment

Comparison of gas-liquid contact mechanism between MU Scrubber and conventional scrubbers

	Type	Gas-Liquid Contact Status
Jet scrubber Venturi scrubber	Dispersed Liquid Type
Packed bed column	Dispersed Liquid Type
Spray column	Dispersed Liquid Type
Perforated-plate column Tray column	Dispersed Gas Type
MU Scrubber	Dispersed Liquid Type

Table4-1. Schematic diagram of gas-liquid contact

	Type of Flow	Type of Gas-Liquid Contact	Gas-Liquid Contact Status
Jet scrubber Venturi scrubber	Parallel-current	Agitation
Packed bed column Spray column	Countercurrent	Agitation
Perforated-plate column Tray column	Countercurrent	Agitation
MU Scrubber	Parallel-current	Mixing

Table4-2. Schematic diagram of mass transfer from the gas phase to the liquid phase

Comparison of performance between MU Scrubber and conventional scrubbers

	Jet Scrubber	Packed Scrubber	MU Scrubber(Static Mixing Scrubber)
Schematic view
Removal efficiency(%)	99-99.5%	90-99	90-99.999
Processable concentration	several100ppm-several1%	several100ppm-several1%	several10ppm-100%
Amount of gas flow	Suitable for small gas flow （10－200ℓ/min）	Suitable for large gas flow （1-100m3/min）	Suitable for both small and large gas flow （1-13,000m3/min）
Clogging inside apparatus	None	Sometimes many due to concentrated dusts and chemicals	None
Pressure drop(kPa)	3-5	0.2-1	2-20
Effect on removal efficiency by change of gas flow	Small (adjustable by bypass line)	Small	Small
Space velocity (m/sec)	Flow speed of throat 30	0.3-2	2-20
Liquid-gas ratio (L/m3)	1,000-3,000	0.5-5	0.2-500
Features	・High removal efficiency ・No nozzle clogging by dust mixing ・Forced liquid-gas mixing condition can be made in throat by liquid atomization with high pressure	・Less pressure drop ・Small amount of circulating liquid	・High removal efficiency ・No nozzle clogging by dust mixing ・No flooding phenomenon ・Suitable for simultaneous processing of gas cooling, gas absorption and dust removal ・High-performance mixing blades called ・MU Mixing Element”are placed inside towers

Table5-1　Comparison of performance between MU Scrubber and conventional scrubbers

	Bubble Column / Scrubber	Packed Scrubber	MU Scrubber(Static Mixing Scrubber)
Schematic view
Removal efficiency(%)	99-99.5%	60	90-99.999
Processable concentration	several 100ppm ー several %	several 100ppm ー several %	several 100ppm ー several %
Amount of gas flow	Suitable for large gas flow (several m3/min – several 100 m3/min)	Suitable for large gas flow (several m3- 100m3/min)	Suitable for both small and large gas flow （1-13,000m3/min）
Clogging inside apparatus	Relatively little compared with Packed Scrubber	Little	None
Pressure drop(kPa)	3-5	0.2-1	0.5-3
Effect on removal efficiency by change of gas flow	Large	Large	Small
Space velocity (m/sec)	1-3	0.2-1	2-20
Liquid-gas ratio (L/m3)	1-3	0.2-1.5	0.2-500
Features	・Simple structure ・More effective than Packed Scrubber in general	・Simple structure ・Generally utilized as previous step of absorption	・High removal efficiency ・No nozzle clogging by dust mixing ・No flooding phenomenon ・Suitable for simultaneous processing of gas cooling, gas absorption and dust removal ・High-performance mixing blades called “MU Mixing Element”are placed inside towers

Table5-2　Comparison of performance between MU Scrubber and conventional scrubbers