A recent paper was published in the journal Nature Climate Change criticizing the Chinese push to produce SNG, synthetic natural gas, from coal and it received a fair amount of commentary describing the plans as an “environmental nightmare”. While some of the criticisms are fair, the authors fail to mention any of the benefits of coal to SNG including the capacity for carbon sequestration and the production of many valuable co-products such as fertilizers and chemicals while also misstating the non-GHG emissions from the process. The paper was written by Chi-Jen Yang and Prof. Robert Jackson from Duke University and it can be found here:
The authors argue that coal to SNG generates substantially higher greenhouse gas emissions and water use over conventional natural gas and due to the high capital costs of the plant the facilities will operate for many years locking in the environmental damage.
Here is some of the commentary from across the net:
China’s plans to cut coal pollution will unleash another environmental catastrophe instead
Synthetic Natural Gas will be China’s (and the World’s) Climate Nightmare
China’s plan to clean up air pollution could be a climate disaster
The authors reference the Great Plains Synfuels Plant in North Dakota, which is the only coal to SNG plant in the USA to justify their cost analysis because that plant had a challenging financial history when it was first built in the 1980’s.
Ironically though, the Great Plains Synfuels plant is the world’s largest and most successful carbon capture and sequestration project in the world. But there is no mention of that anywhere in the paper while the authors go on at length stating how high the carbon emissions are from coal to SNG.
The authors are also mistaken in stating that, “in addition to GHG emissions, the production of coal-fuelled SNG emits hydrogen sulphide and mercury that, if not properly scrubbed or treated, are potentially harmful.” This assertion reflects a complete misunderstanding of how coal to SNG works because the catalytic conversion process requires that the gasses be completely scrubbed already. The sulfur products as well as heavy metals, particulates and any other contaminants are completely removed and most are converted into useful commodities.
So how does coal to SNG work?
Here is process flow chart from the Great Plains Synfuels website. www.dakotagas.comCoal gasification is one of the oldest of all industrial processes with a history going back to the 1800’s. In the early days coal gasification was used to crudely convert coal to a product called “town gas” that was used to light city street lamps. These were some of the earliest municipal utilities. The process was effective but dirty and was eventually replaced by natural gas and electric distribution in most places.
Gasification works by heating up carbon feedstocks such as: coal, biomass, garbage or petcoke inside a sealed vessel with controlled oxygen so that the feedstocks are not allowed to combust but instead break down into a gas called syngas. Syngas is a blend of mostly carbon monoxide and hydrogen and it is a valuable intermediate product in industry that is converted into a wide variety of end products such as liquid fuels, chemicals, electricity or methane (natural gas).
Syngas is very dirty with acids when it first comes out of the gasifier and may contain hydrogen sulfide, particulates, metals and other stuff so it must be scrubbed. In the Great Plains plant the acid gas and other contaminants are removed through the widely used Rectisol process that reacts the sulfur with methanol and converts into an elemental form that is then processed into commodity products. The Rectisol process also separates out carbon dioxide in a pure form and this is one of the most proven methods for carbon capture and sequestration. The now clean syngas, CO-H, is treated with a catalyst to convert it into methane, CH4, which is sold as commodity natural gas.
At the Great Plains plant the CO2 is injected into a pipeline and transported up into Canada where it is sold and used in oil drilling for Enhanced Oil Recovery (EOR). As of today EOR is the most promising method for carbon sequestration. CO2 for EOR is very effective at improving the production of oil wells because the CO2 reacts with the petroleum to reduce its viscosity and help it flow through the underground formations. When used for EOR CO2 is a valuable commodity that is sold for profit. The challenge in this business is that it requires a pipeline between the gasifier and the oil fields and those pipelines are not common. At the Great Plains plant, nearly 50% of the produced CO2 is sequestered and it is done profitably.
Aside from CH4 and CO2, the Great Plains plant also produces these valuable products: Ammonium Sulfate fertilizer from sulfur, Anhydrous Ammonia fertilizer, Dephonlized Cresylic Acid an industrial chemical, Krypton and Xenon gases, Liquid Nitrogen, Naptha and Phenol. Natural gas is not even their most valuable product.
So to come back to the paper from Duke, I agree with the author’s contentions that coal to SNG is going to have higher greenhouse gas emissions than alternatives such as natural gas. Biomethane, coalbed methane, hydrofracked methane all have lower GHG and are more desirable than coal SNG. I also agree with the authors that water use in arid regions is a serious issue and must be handled in a sustainable manner. These are both very valid concerns but I disagree with the authors that SNG is inherently an “environmental nightmare” and I feel that they fail to put the entire process into proper context. Coal conversion when done right is certainly an improvement over burning coal directly. The toxic constituents of coal that cause pollution when combusted are instead removed and converted in a variety of valuable commodities when gasified, this is the essence of transforming liabilities into assets, and this not speculative but completely proven at industrial scales.
Secondly, the failure to mention carbon capture and sequestration is severely misleading. While the Chinese may not plan to implement the technology today the plants being built are certainly carbon capture ready and that deserves to be mentioned, especially since the authors detail the Great Plains Synfuels plant and never mention that specific facility is currently the worlds leader and model for successful CCS. The Great Plains plant did not have CCS when first built in 1984 it was added later, so there is no reason to think that the Chinese could not do the same as well. To speculate on lifetime carbon emissions the Chinese plants may produce without speculating about the possibility of adding CCS is not fair.
I have been in touch with the author Chi-Jen Yang as well as representatives from Dakota Gas. Mr. Yang is very knowledgeable about the Chinese natural gas markets and educated me regarding some of the history and policy. He pointed out that currently Chinese policy has the country venting coal bed methane in mines that could be captured and I agree with him entirely that these gasses should be captured and used because they are a very valuable fuel and when released are a potent greenhouse gas. It seems like lose-lose to vent coalbed methane when they are seeking to convert coal to methane elsewhere. This is similar to the oil wells in North Dakota where significant methane is being flared because they lack sufficient infrastructure to bring the gas to market. Mr. Yang also educated me regarding the inefficiencies in the Chinese natural gas market where price controls are interfering with the development of their large domestic gas resources. Again, it is unfortunate to have bad policy causing good resources to be underutilized while elsewhere they seek out more invasive forms of energy.
I look forward to continuing this conversation between the authors as well as folks from Dakota Gas who have promised a response of their own.
Personally, I think we are not going to see the end of coal anytime and it is important that we learn to use it in the best manner possible. Gasification technologies offer the ability to convert a wide variety of dirty fuels into high performance ultra clean fuels that can out perform conventional coal and petroleum while simultaneously transforming the toxic contaminants into valuable commodities. This true when using garbage, low grade coal or dirty petcoke as feedstocks. I think we should encourage these technologies while always keeping in mind that they need to be placed in the appropriate locations and built to the proper scales.
I was very troubled when I read all the commentary about this paper and referring to Chinese SNG as just the latest Chinese environmental nightmare. In the mind of the average environmentalist when you combine the words China and coal it is like the boogeyman squared and that is very unfortunate because in this case I think the technology is being mischaracterized.