Mitsubishi Heavy Industries Technical Review Vol. 61 No. 2 (June 2024)
1Commercialization of Hybrid Bag Filter® (HBF)
Made of Polytetrafluoroethylene (PTFE)
with Capability of Decomposing Dioxins andReducing Environmental Impact

MASATOSHI KATSUKI*1

TAKUMI SUZUKI*2

YUKI ASAI*3

TAIJI UCHIDA*4

KEISHIRO JITSUKAWA*4

KYOHEI SAKURAI*4

Ahead of their competitors, Mitsubishi Heavy Industries, Ltd. (MHI) and MHI Environmental& Chemical Engineering Co., Ltd. (MHIEC) have developed and made commercially available a VTi catalyst-supported bag filter called the Hybrid Bag Filter® (HBF). HBF simultaneously enables,desalination, desulfurization, dust removal, denitrification and removal of dioxins (DXNs) (by meansof filtration, adsorption, and catalytic decomposition)(1)-(6). Recently, we have succeeded indeveloping the filter cloth base material of HBF from conventional glass fiber topolytetrafluoroethylene (PTFE), and verified the high level of performance when used in an actualunit.

|1. Introduction
Although the filter cloth to support the catalyst is conventionally made of glass fiber, thedurability is expected to improve if PTFE, which has superior chemical stability and wear resistance,
can be used instead. However, because of its strong water repellency, PTFE has difficulty insupporting the catalyst on the filter cloth with the conventional catalyst slurry coating technology.
MHI has successfully developed an original technology to support the catalyst on PTFE filter
cloth. The HBF made of this PTFE filter cloth was then applied in an actual unit. The results, whichindicate its high level of operational performance, are presented in this report.

|2. Hybrid Bag Filter® (HBF)In HBF, the filter fabric is coated with the catalyst using our original technology. Whileretaining the capability to remove harmful substances generally expected in waste incinerator
applications, our HBF, which is a highly functional filter cloth, further removes gaseous DXNs anddecomposes NOx (denitrification). Figure 1 gives a microscopic view of HBF, while Figure 2 is aconceptual diagram of its functions. HBF’s conditions and manufacturing method are adjusted
depending on the required performance of flue gas treatment, thus making it possible to use different
types of HBF accordingly, that is, either one dedicated to removing DXNs or the other that also has
denitrification capabilities.
This report focuses on the type of HBF used for DXNs removal only. The applications of thistype of HBF have been increasing in recent years.

*1

Deputy Senior Director, Ecosystems Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.

*2

Chief Staff Researcher, Ecosystems Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.

*3

Chemical Research Department, Mitsubishi Heavy Industries, Ltd.

*4

Design Unit, Engineering Division, Mitsubishi Heavy Industries Environmental & Chemical Engineering Co., Ltd.

Mitsubishi Heavy Industries Technical Review Vol. 61 No. 2 (June 2024)
2Figure 1

Microscopic view of HBFFigure 2

Conceptual diagram of HBF|3. Background to development and performance assessment
3.1

Advantages of PTFE as filter cloth over glass fiber

As for the filter cloth of bag filters generally used in waste incinerators, glass fiber has beenmostly used so far. However, the applications of PTFE have been increasing in recent years. This inpart is attributed to their differences in strength. Figure 3 shows the test results of tensile strength
over time for both PTFE and glass fiber filter cloths in an actual unit. When comparing their residual
rates of tensile strength, PTFE is superior to glass fiber. We therefore took up the challenge to makeit possible for this superior durability of PTFE filter cloth to be utilized fully in the HBF application
as well, and started developing an HBF made of PTFE.

Figure 3 Residual rates of tensile strength of filter cloths
used in actual unit

3.2

Challenge of supporting catalyst on PTFE filter cloth

In the case of glass fiber HBF, a catalyst slurry prepared in water medium is applied. However,as PTFE is strongly water repellent, this application method cannot achieve adequate penetration of
the slurry into the PTFE filter cloth, making it impossible for a sufficient amount of catalyst to besupported uniformly on the cloth.

3.3

Our solution to problem

Since the affinity with the filter cloth needs to be improved for the successful application of
catalyst slurry onto the strongly water-repellent PTFE, our approach focuses on the contact angle ofMitsubishi Heavy Industries Technical Review Vol. 61 No. 2 (June 2024)
3

catalyst slurry (Figure 4). As the conventional catalyst slurry is water-based, its application onto thefilter cloth is not good enough to allow the slurry to penetrate into the cloth, and instead results inthe formation of aggregates on the surface of the cloth. Therefore, uniform supporting of a sufficientamount of catalyst is impossible.
However, we found out that the contact angle of catalyst slurry can be controlled by adding asurfactant to the slurry. As shown in Figure 5, the contact angle can be considerably reduced in thisway. When this catalyst slurry is applied, the catalyst can penetrate about five times deeper than theconventional one (Figure 6).

Figure 4

Conceptual diagram of contact angle

Figure 5 Relationship between surfactant concentration and contact
angle of catalyst slurry

Figure 6 Depths of catalyst penetration into HBFs produced with twocatalyst supporting methods: newly developed and conventional

Mitsubishi Heavy Industries Technical Review Vol. 61 No. 2 (June 2024)
43.4

Performance assessment method for HBF made of PTFE

The prototyped PTFE HBF was assessed in terms of differential pressure, denitrification rate.
In this assessment, various data on performance were obtained by passing a gas that simulates thewaste incinerator flue gas through a portion of the PTFE HBF filter cloth.

3.5

Performance assessment test results and interpretation

Given in Figure 7 are the assessment results of differential pressure and denitrification rate.
According to the differential pressure results, a 48% reduction can be achieved by PTFE HBF
when compared with the previous model (i.e., glass fiber HBF).
PTFE HBF can improve the denitrification rate by 53% from the level of the previous model.
As described above, all the obtained results indicate that the superiority of the new model overthe previous one. In this test, the denitrification rate has been assessed, although the new model isintended for use to remove DXNs in actual operations. This is because it is not possible to measure
the DXNs removal rate with the use of simulated gas.

Figure 7 Simulated gas test results of differential pressure, denitrification rate, and rate ofcatalysts detaching|4. Actual unit applications and status of their operations
4.1

Plants with the use of PTFE HBF

We mass-produced PTFE HBFs and applied them to domestic plant A (a general wasteincinerator with the treatment capacity of 75 t/24 h), and overseas plant B (a general waste incinerator
with the treatment capacity of 1,050 t/24 h). The DXNs removal performance and temporal changes
in differential pressure were assessed.

4.2

DXNs removal performance

Table 1 gives the DXNs removal rate results obtained by simultaneously measuring at the inlet
and outlet of the bag filter of domestic plant A. Both particulate and gaseous DXNs were analyzed.
The results show that the removal rate of either DXN type is 99% or higher, confirming the excellent
removal performance.
Table 1 Removal rates of particulate and gaseous DXNs at plant A
Place of measurement Unit of measurement

4.3
(1)

3

Particulate DXNs

Gaseous DXNs

Total

Bag filter inlet[ng-TEQ/Nm ]

0.79

1.1

1.89

Bag filter outlet[ng-TEQ/Nm3]

0.00038

0.00270.00308

Removal rate[％]

99.95

99.75

99.84

Temporal changes in differential pressureChanges in differential pressure at domestic plant A
Figure 8 is a chart in which the differential pressure is plotted against time for the previousmodel and the PTFE HBF. The data were measured for 140 days after the start of operation using
the differential pressure gauge installed at the inlet/outlet of the bag filter of domestic plant A.
Apart from the temporary shutdowns of the incinerator, the PTFE HBF can operate in a stablemanner at differential pressures that are about 20% lower than the previous model on average.

Mitsubishi Heavy Industries Technical Review Vol. 61 No. 2 (June 2024)
5Figure 8(2)Temporal changes in differential pressure (domestic plant A)

Changes in differential pressure at overseas plant B
Likewise, plotted on the chart in Figure 9 are the differential pressure changes with time
regarding the previous model and the PTFE HBF. The data were measured for almost 80 days
after the start of operation using the differential pressure gauge installed at the inlet/outlet of thebag filter of overseas plant B. When compared with the previous model, the PTFE HBF can
operate in a stable manner at differential pressures that are about 33% lower on average.

Figure 9

Temporal changes in differential pressure (overseas plant B)

As described in (1) and (2), the use of PTFE HBF in actual units also produced better resultsin terms of differential pressure, which allows backwash to be performed less frequently, while
maintaining the backwash air pressure lower than the previous model. This in turn causes less friction
between the HBF and the metal part of the retainer, when the passage of gas is resumed afterbackwash. The wear of HBF can thus be minimized. Higher durability can therefore be expected.

|5. Effects of running cost reduction and fewer CO2 emissions
5.1

Running cost reduction effect

In the case of another domestic plant C general waste incinerator (treatment capacity: 175 t/24h), in which the glass fiber HBF is currently in use, it has been estimated that replacing it with thePTFE HBF can cut the running costs of a flue gas treatment facility by 57%, based on the following
three improvements:(1) The service life is expected to double, because of the improved durability of HBF.
(2) The consumption of electricity by the downstream induced draft fan can be reduced by 27%,
as a result of the lowered operating differential pressure of the bag filter.

Mitsubishi Heavy Industries Technical Review Vol. 61 No. 2 (June 2024)
65.2

CO2 emissions reduction effectAs described in section 4.3, replacing the glass fiber HBF with the PTFE HBF can reduce thedifferential pressure, which leads to less power required for the induced draft fan. This means that
reduction of CO2 emissions can eventually be expected. The effect in this regard was estimated.
With regard to the flue gas treatment facility, the effect of CO2 emissions reduction resulting
from the replacement by the PTFE HBF was estimated based on the actual operational data
before/after the replacement and the reduction rate of differential pressure. The results show thatdomestic plant A can reduce the emissions by 20% and overseas plant B by 29%.

|6. Conclusion
Having developed a manufacturing technology that enables the catalyst slurry to be applied
onto water-repellent PTFE, we obtained the following results:(1) The results of operating the PTFE HBF in actual units have confirmed that the removal rates
of both particulate and gaseous DXNs are as high as 99% or more, exhibiting excellent
removal performance.
(2) The operating differential pressure of PTFE HBF is about 20% lower than that of glass fiber
HBF, achieving stable operation for 140 days from the start of operation (excluding thetemporary shutdowns) at domestic plant A. Overseas plant B has also been in stable operation
for nearly 80 days from the start of operation at a differential pressure about 33% lower.
(3) With regard to domestic plant C in which the glass fiber HBF is currently in use, it has been
estimated that a 57% reduction in the running costs of a flue gas treatment facility is possible,
if the glass fiber HBF is replaced by the PTFE HBF.
(4) According to the estimations of CO2 emissions from the flue gas treatment facility, domestic
plant A is expected to reduce emissions by 20% with the use of PTFE HBF and overseas
plant B by 29%.
The addition of this newly developed PTFE HBF to our product portfolio enables us to makea more tailor-made proposal according to a customer’s needs including the required performance,durability and price, by selecting a suitable one from the available product options of normal bagfilter, glass fiber HBF and PTFE HBF. As at March 2024, the operation of PTFE HBF at a differential
pressure lower than the glass fiber HBF was continuing in a stable manner at both of the domestic
and overseas plants. Further expansion of its application is therefore expected.

“Hybrid Bag Filter®” is a registered trademark of MHIEC in Japan.

References
(1)
(2)
(3)
(4)
(5)

(6)

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