Principal Research Results

Development of Ice/Oil/PCB Elimination Technology using DME

Background
There is a pressing need for low-cost dewatering of high-water-content solids such as coal and sewage sludge. Pre-existing
technologies consume a great amount of energy due to their reliance on high temperature to evaporate the water content out of solid
substances. In this research, we turned our attention to coal and sewage sludge; using dimethyl ether (DME)＊ 1. In this method, thewater contained in coal is extracted into liquefied DME for separation from coal. After dewatering, DME is depressurized and subsequently vaporizes, thereby leaving the water to be separated at room temperature. There is already a clear advantage in energy
efficiency, according to full-scale performance test calculations for the DME dewatering process. At the present time, we are focusing
on understanding the technology's suitability for cold-weather regions, as well as its ability to eliminate substances such as oil andPCB.

Objective
Our objective is to verify the practicable possibilities for expanding first the elimination of ice in cold-weather regions, andlater the elimination of oils and PCB at room temperature, using the DME desiccation method on materials other than the traditionaltarget material, water.

Principal Results
1. Potential to remove ice from frozen coal and wood pieces in a sub-zero environment
We installed a test-tube level (10 ml/batch) DME desiccation test device (Fig. 1) in an environment kept at a constanttemperature of -10℃, and were then able to use liquefied DME to extract 44.5% of the icy moisture content from sub-bituminous coal(particulate diameter: 4-8 mm, moisture content: 42.4 wt%). Similarly, we were able to use liquefied DME to extract 53.5% volume ofice from frozen cedar chips (length: ~1 cm, thickness: 1-3 mm, moisture content: 68.9 wt%) in an environment kept at a constanttemperature of -23℃.
2. Capability of removing a variety of oils from a variety of materials at room temperature
We let vacuum pump oil to adsorb into an artificial oil-absorbing sheet, and then used our laboratory's prototype to bringliquefied DME into contact with the oil-soaked sheet. We estimated that this would be the most difficult form of oil removal, but theresults of our experiment showed that we succeeded in removing all the oil from the absorbent sheet at room temperature.
Furthermore, we also succeeded in removing all the oil from glass, wood pieces, paper and metal that had been covered in insulatingoil. In addition, we succeeded in removing both the moisture content and the oil, simultaneously, from damp soil that had been permeated with heavy oil (Fig. 2).
3. Room-temperature PCB removal from high moisture content sediment polluted with PCB
We brought PCB-polluted river sediment ＊ 2 with a high moisture content into contact with liquefied DME. At room temperature, we were able to remove more than 99% of the PCB from the high moisture content sediment, and were simultaneously able toremove the moisture content (Fig. 3), thereby succeeding in cleansing the sediment of PCB such that PCB density levels were at or
below environmental standard levels (dioxin poison volume 150 pg-TEQ/g).
(The PCB-removal research was carried out in conjunction with Associate Professor Takaoka and Assistant Professor Oshita of Kyoto
University, Faculty of Engineering, Urban and Environmental Engineering.)

Future Developments
We will continue to study the practical applications of the DME desiccation technology verified on the removal targets ofthe current experiments.
Main Researcher: Hideki Kanda, Ph. D.,
Research Scientist, Fuel Reforming Engineering Sector, Energy Engineering Research Laboratory
Reference
Affiliated Reports: H. Kanda, and H. Makino., 2008, “The development of room-temperature oil-removal processes using recycle
extraction-use liquefied DME”, CRIEPI Report: M07009; “Evaluation of the suitability of liquefied DME dewatering technology forfrozen solid fuel desiccation at sub-zero temperatures”, CRIEPI Report: M07013＊1：Standard boiling point: -25℃; boiling point at 0.5MP: 20℃. Not only water, but also ice, oil and PCB were dissolved into the liquid-state
DME. In China, it is rapidly being propagated as a cheap alternative to imported LPG, and is a next-generation green fuel.
＊2：Due to past illegal discarding and dumping, there are rivers in which slime has been detected with PCB in excess of allowed levels. Although
there have been studies on the use of acetone in PCB removal, the water in slime interferes with this process, in addition to which, the acetone
remaining behind as residue in the soil gives rise to a new set of problems, all of which make this method difficult to implement.
Awards won since last year's annual report: Environmental Technology/Project Award, Environmental Engineering Forum, Japan Society of Civil
Engineers; The Chemical Society of Japan Award for Young Chemists in Technical Development for 2007; Fuji-Sankei-Business-I Award (ViceGrand Prize), 22nd Advanced Technology Award established by Kenichi FUKUI.

106

6. Fossil Fuel Power Generation

Fig.1 Left: Overview of the Test Device; Right: Photograph showing ethanol temperature(−23°C for wood chips)
Coal is produced in abundance even in overseas northern climes and inland cold-weather areas. In these cold-weather
regions, the temperature in winter falls below the freezing point of water. For this reason, using DME to directly
remove icy moisture from frozen coal slurry without having to melt the moisture itself is an effective desiccation
method. The results of this experiment verified this practical possibility.

：オイルソーベント
0.34kg：
オイルソーベント
0.34kgOil-sorbent
Sheet:
0.34kg

真空ポンプ+2.60kg
油：
真空ポ
プ油：
60kg
Vacuumン
Pump
Oil:+2.
+2.60kg

真空ポンプ-2.70kg-2.70kVacuum Pump油：
Oil: −
2.70 kg g

ＤＭＥ
１００Ｌ

：
土壌
3.63k
：
3.63kgSoil:
3.63 kg g：-0.75kg kg
Moisture− 0.75
水分Content:
Heavy
Oil:
1.15kg−
重油：-1.15k g

Heavy：
Oil:+1.15 kg
重油
+1.15kg
重油+1.15kg

重油：-1.15k g

ＤＭＥ
１００Ｌ

6Fig.2 Removal of oil from oil-absorbent sheets and moist soil

Fig.3 River sediment from which PCB has been removed with thehelp of DME (left: before DME contact; middle: after DMEcontact; right: waste liquid including PCB) (Photographs
courtesy of Associate Prof. Takaoka and Assistant Prof. Oshitaof Kyoto Univ., Urban and Environmental Engineering)107

After PCB has been
removedwithDME,
sediment becomes paler incolor and shrinks. This isbecause the slime is also
desiccated simultaneously,
which has a moisture
content of 60%. Because
DME is a gas at normal
temperatures and pressures,it does not leave anyresidue. For this reason, it
has clearly become acandidate for application as
an environmental cleansing
technology.