|DME is a component of China’s vision for coal utilization.|
Japan’s Toyo Engineering will design and build China’s first major coal-to-dimethyl ether (DME) with China’s Ningxia Coal Group in northwestern China’s Ningxia Hui Autonomous Region.
DME can serve as a synthetic fuel that is to diesel what LPG is to gasoline. It is gaseous at ambient conditions but can be liquefied at moderate pressure. With a high cetane number, DME has very attractive characteristics as an alternative fuel for diesel engines.
DME is clean-burning, sulfur-free, with extremely low particulates. A dedicated DME vehicle might not require a particulate filter but would need a purpose-designed fuel handling and injection system as well as a lubricating additive.
The Ningxia DME plant will have an initial production capacity of 210,000 tonnes of DME annually and is to be completed at the end of 2007. The facility will be part of a larger petrochemical complex.
This will mark Toyo’s second major DME initiative in China. The company is completing a 110,000-tonne per year DME plant for the Lutianhua Group in Sichuan province. This plant, which uses natural gas as its feedstock, is due to come online early next year.
DME automobile project. China’s Ministry of Science and Technology recently announced the successful development of a Euro-3-compliant prototype DME-fueled automobile. The test car, built by FAW Dalian Diesel Engine Factory, Xi’an Jiaotong University and Wuxi Fuel Injection Equipment Research Institute, has logged some 4,500 kilometers so far.
The researchers in the “Dimethyl Ether Automobiles R&D Project” are examining:
High- and low-pressure fuel injection systems to handle DME’s low viscosity and low boiling point
Optimization of the combustion system
|Physical properties and combustion characteristics of DME|
|Boiling point (ºC)||-25.1||-42.0||-161.5||180–370|
|Liquid density (g/cm3 @20ºC)||0.67||0.49||0.42||0.84|
|Liquid viscosity (kg/ms @25ºC)||0.12–0.15||0.2||–||2–4|
|Specific gravity of gas (vs. air)||1.59||1.52||0.55||–|
|Vapor pressure (MPa @25ºC)||0.61||0.93||–||–|
|Explosion limit (%)||3.4–17||2.1–9.4||5–15||0.6–6.5|
|Net calorific value (MJ/Nm3)||59.3||91.0||35.9||–|
|Net calorific value (MJ/kg)||28.8||46.3||49.0||42.7|
DME Production. In the coal production pathway, coal is first gassified to produce a syngas rich in CO and hydrogen. The syngas is then put through the water gas shift reaction (CO + H2O → H2+ CO2) to maximize conversion in the synthesis reactor.
|Without carbon capture, the fuel cycle GHG emissions from coal-based DME are almost twice that of gasoline on an energy-equivalent basis.|
Acid gases (H2S and CO2) and other impurities are removed from the syngas, which then moves to the synthesis reactor for production into DME. By-produced CO2, methanol and water are separated from the product DME in the distillation columns. Methanol is recycled to DME synthesis reactor to be converted into DME.
This coal-based process can be quite CO2-intensive, and would need to be implemented with a strategy for carbon capture and sequestration to fit into any sort of regime for mitigating greenhouse gas emissions.
Because of the abundance of coal in China, and its ever-growing demand for energy, the country will remain dependent on the ultimate carbon fuel for decades to come. Accordingly, developing coal-based polygeneration strategies is of intense interest and exploration in the country. DME as a diesel substitute will be part of that.
Coal Conversion into Dimethyl Ether as an Innovative Clean Fuel, Yotaro Ohno, Mamoru Omiya; JFE Holdings, Inc.
Synthetic Liquid Fuels from Coal and Biomass with Near-Zero GHG Emissions, Robert H. Williams, Princeton Environmental Institute
Energy and Advanced Coal Utilization Strategy in China, Prof. Ni Weidou, Tsinghua University