By John Richardson

Coal2OctoberIT has become the accepted wisdom over the last few years that the coal-to-olefins (CTO) process in China consumes a lot of water.

This theory has been expressed in so many conference papers and in research papers that this “truism” is part of just about every discussion on the viability of CTO projects.

But what if the water issue is, in fact, nothing more than a great urban myth, an apocryphal tale that has developed a life of its own?

Duncan Seddon, a Melbourne Australia-based oil, gas and chemicals consultant argues to this effect when he says the following:

  • The gasification of coal uses oxygen, which is produced from large air separation units. Virtually all of this oxygen is converted into water; this water can thus be used as process water with minimal clean-up. There is some requirement for make-up water (boiler quality) but this is not large.
  • In addition, coal generally contains a lot of moisture (especially for sub-bituminous or lignite – Latrobe valley lignite – this is 60% water). There are technologies out there to extract water from this type of coal, which can then, of course, be used in further processes.
  • But there is an issue around cooling when the methanol-to-olefins (MTO) stage is reached, as the MTO process works at 50% thermal efficiency. This means that 50% of the coal used is in effect burned and the heat generated has to be discharged to the environment.
  • An easy, and cheap, way of doing this cooling is to use river water for cooling, and so this is where you can end up with huge consumption of water per tonne of olefins produced.
  • But there is no reason, other than capital costs, to use river water as you can instead use:
  1. A cooling tower, where a circuit of cooling water is used. Up to 15% of water can disappear into the atmosphere out of the top of these cooling towers, but it is also possible to further invest in a closed-loop system, which re-condenses the steam.
  2. Another approach is to air cool plants, which means you would use no water for cooling at all in the MTO step.

And so, if Seddon’s views are accurate, it doesn’t necessarily matter a jot that many of  the CTO projects are in arid areas, where water is in tight supply.

Why? Because, potentially, they can be net producers of water, provided the right capital spending takes place.

Back in July, a source with an oil, gas and chemicals company also suggested that water was not an issue for the CTO process in China. However, his argument was different. He claimed that whilst the process did, indeed, consume a lot of water, the government was determined, for energy security reasons, to get over the problem.

Obviously, though, if Seddon’s views are accurate, tackling the water issue it is just a question, as we said, of money  – and  does not require, as many people think, technological innovation. Cooling towers and air cooling are technologies that have been around for many years.

One could argue, of course, that CTO is still an environmentally harmful process in terms of sulphur, particulate matter and carbon emissions.

But as we also discussed in our July post, there is another important argument here: Because  gasification projects often involve making synthetic natural gas that replaces coal in power generation, the gasification process can help solve China’s air pollution problems. If they are making lots of synthetic natural gas, diesel, gasoline etc. in a big integrated complex, adding methanol-to-olefins adds a bit more economic value – and crucially, also, social value to such a complex.

On the angle of water, the environmentalists might be barking up the wrong tree by claiming that these projects always, by their very nature, consume a lot of water. They should instead, perhaps, be pressurising project proponents to spend money on cooling towers etc.

This could also be another test for the viability of a particular project. If it doesn’t include a cooling tower or air cooling in its configuration, will it get approval if it is located in an arid area?

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