180
Alternative Fuels for Transportation
is an excess of carbon, and when it is greater than one, there is an excess of
CO. The amounts of water and methanol produced are small, and there is a
tendency for the amount of water produced to increase at large H 2 /CO ratios.
The amount of other products than DME indicates the need to process the
gas to remove the DME product and unwanted components, and to recycle
unreacted syngas components. In order to maintain H 2 /CO ratio at one, the
CO 2 can be recycled and added to the reformer, Reaction 6.4.
The most efficient and economic process was stated to be the direct process
(Hansen et al. 1995). However, there is an advantage to producing methanol
separately and then dehydrating as shown in Figure 6.4, as one can choose
the final product mix, and produce the most economically attractive product
mix for existing market conditions. It is difficult to determine the economic
differences between the two, as comparable units of direct and indirect production of DME at full economic scale are not yet completed at the time of
writing.
There is an additional advantage to the use of methanol dehydration to
produce DME, especially in the initial stages. This is due to the established
methanol market and production system. In recent years, the production
of methanol has been shifted to larger plants, which produce methanol in
amounts on the order of 5000 tons per day. This gives an economic advantage
compared to smaller older plants, and combined with a sluggish methanol
market due to the restriction of methyl tert butyl ether (MTBE) in gasoline,
has resulted in an excess production capacity for methanol on a worldwide
basis. Such existing capacity can be converted to DME production for a very
much lower cost than the construction of a new DME plant. A new DME production facility on the scale of 5000 tons/day is estimated to cost in excess of
500 million U.S. dollars (JDF 2007). The addition of a methanol dehydration
unit would cost on the order of a 10th of this. So especially in the introductory stage of DME use, conversion of these existing, smaller methanol plants
could significantly reduce initial production investment costs, and help to
solve the “chicken-egg” problem, so common with the introduction of alternative fuels. The first DME used in the marketplace for home heating and
cooking in China has been produced from excess methanol capacity.
DME produced for aerosol cans has been produced by methanol dehydration, and was previously considered to be too expensive to be used as a fuel.
This high price has been due to two factors. The first is the low production
volume. Total current annual world consumption of DME is on the order of
150,000 tons per year (JDF 2007), much smaller than the proposed value of
around a million tons per year, even if it all was concentrated in one place,
which is not the case. The second is the requirement for very high purity of
DME, since aerosol sprays come in close contact with people and quality must
be carefully controlled. DME fuel quality can be much lower than this, which
gives a significant price reduction combined with larger scale production.
The major impurities expected in fuel grade DME are methanol and water
as seen from Figure 6.8. Figure 6.9 shows the region of acceptable ignition in
Alternative Fuels for Transportation
is an excess of carbon, and when it is greater than one, there is an excess of
CO. The amounts of water and methanol produced are small, and there is a
tendency for the amount of water produced to increase at large H 2 /CO ratios.
The amount of other products than DME indicates the need to process the
gas to remove the DME product and unwanted components, and to recycle
unreacted syngas components. In order to maintain H 2 /CO ratio at one, the
CO 2 can be recycled and added to the reformer, Reaction 6.4.
The most efficient and economic process was stated to be the direct process
(Hansen et al. 1995). However, there is an advantage to producing methanol
separately and then dehydrating as shown in Figure 6.4, as one can choose
the final product mix, and produce the most economically attractive product
mix for existing market conditions. It is difficult to determine the economic
differences between the two, as comparable units of direct and indirect production of DME at full economic scale are not yet completed at the time of
writing.
There is an additional advantage to the use of methanol dehydration to
produce DME, especially in the initial stages. This is due to the established
methanol market and production system. In recent years, the production
of methanol has been shifted to larger plants, which produce methanol in
amounts on the order of 5000 tons per day. This gives an economic advantage
compared to smaller older plants, and combined with a sluggish methanol
market due to the restriction of methyl tert butyl ether (MTBE) in gasoline,
has resulted in an excess production capacity for methanol on a worldwide
basis. Such existing capacity can be converted to DME production for a very
much lower cost than the construction of a new DME plant. A new DME production facility on the scale of 5000 tons/day is estimated to cost in excess of
500 million U.S. dollars (JDF 2007). The addition of a methanol dehydration
unit would cost on the order of a 10th of this. So especially in the introductory stage of DME use, conversion of these existing, smaller methanol plants
could significantly reduce initial production investment costs, and help to
solve the “chicken-egg” problem, so common with the introduction of alternative fuels. The first DME used in the marketplace for home heating and
cooking in China has been produced from excess methanol capacity.
DME produced for aerosol cans has been produced by methanol dehydration, and was previously considered to be too expensive to be used as a fuel.
This high price has been due to two factors. The first is the low production
volume. Total current annual world consumption of DME is on the order of
150,000 tons per year (JDF 2007), much smaller than the proposed value of
around a million tons per year, even if it all was concentrated in one place,
which is not the case. The second is the requirement for very high purity of
DME, since aerosol sprays come in close contact with people and quality must
be carefully controlled. DME fuel quality can be much lower than this, which
gives a significant price reduction combined with larger scale production.
The major impurities expected in fuel grade DME are methanol and water
as seen from Figure 6.8. Figure 6.9 shows the region of acceptable ignition in