Syngas Technology Renaissance of Syngas Technology
The Chemical Process Industry is making a concerted effort to find an alternative to oil. Natural gas, coal and biomass are all potential sources of basic chemicals, and syngas production can make a bigger contribution than it has so far.
The reaction of a time traveler from the early days of the Chemical Process Industry (CPI) to the current renaissance of syngas production might well be a feeling of déjà vu. Process engineers and scientists in Europe are working on gasification technologies for converting wood, plant residue or bio-waste into a reactive mixture of hydrogen and carbon monoxide for the production of either fuel or basic chemicals. Integrated chemical complexes are being built in China to gasify coal for subsequent conversion to propylene and ethylene. Despite the differences, the Fischer-Tropsch process, the Megamethanol process and oxo-synthesis all have one thing in common: syngas production always plays a key role. That is good news for large engineering contractors. Major players that have the right technology and the capability to take on large-scale EPC projects are e.g. Linde, the Air Liquide subsidiary Lurgi, Uhde as well as Technip, Matthei Johnson and Kellogg. All of them are busy at the moment. Linde is building a gasification plant in South Korea with a capacity of 500,000 metric tons, which is expected to go online in 2013. Lurgi has taken its Megamethanol technology to China, where it is working in partnership with Shenhua Ninxia and Datang Duolon (470,000 t/a of propylene each). Uhde has just received the go-ahead to use its Prenflow biomass gasification process in collaboration with five French partners on the French BioTfueL Project.
Syngas Technology: Greetings From The Past
If you put the history of chemical production on a timeline, you will see that syngas plants are dinosaurs from the early days of the CPI when olefins such as propylene and ethylene were produced from coal. It wasn’t until the beginning of the 1950s when the first large oil fields were developed that oil became cheaper than any alternative, the reserves appeared to be inexhaustible and oil provided a far wider range of basic chemicals than syngas or coke. Syngas has continued to play a role in the production of methanol, ammonia and hydrogen, but since oil became dominant propylene and ethylene have been produced in crackers.
However recently, oil prices have repeatedly tested the $ 100/barrel threshold, and the experts at BP, Shell, etc. continue to revise their oil reserve scenarios. These developments have injected new life into technologies such as Fischer-Tropsch and syngas production. Even the Imbert wood gas generator is making a comeback, on a Ford just like years ago. “Syngas technologies run in cycles,” said Prof. Eckhard Dinjus, head of the Institute of Catalytic Research and Technology (IKFT) at the German Karlsruhe Institute of Technology (KIT).
Versatile Raw Material Can Be Used
Two industries are currently working on syngas production, one of them being the fuel industry which uses gas as an intermediate for biofuel. The Chemical Process Industry has also developed a renewed interest in the process. The reactive carbon monoxide-hydrogen mixture is highly versatile. Dr. Andreas Kreitmeier, who is in charge of research at BASF, sees this as a genuine advantage. He stated at a press conference three years ago that the use of syngas is likely to broaden the raw material base.
Syngas can be produced from nearly any raw material that contains carbon. Coal, natural gas, oil, plant residue, bio-waste, wood, plastic and even garbage have already been gasified. This gives the Chemical Process Industry the flexibility it needs and means that gas will play a major role in the search for new raw materials. There is good reason why BASF invested € 100 million in a research cluster between 2006 and 2008. Among other things, the company’s researchers are working on catalysts for Fischer-Tropsch synthesis which can be used specifically for production of olefins with two, three or four carbon atoms.
Syngas is raw material neutral
Once it has been produced, syngas is essentially raw material neutral. However the original input material has an influence on the hydrogen/carbon ratio. The range extends from 1:1 for coal and biomass to 4:1 for methane-rich natural gas. Oil lies in the middle at 2:1. In other words, synthesis in and of itself is not the whole story. There are also downstream cleaning stages, and in most cases catalytic conversion is used to increase the proportion of hydrogen in the hydrogen/carbon ratio depending on how the gas will be used.
That makes the use of biomass particularly challenging. “Biomass is a catch-all term for a very heterogeneous class of materials,” explained Dinjus, a co-developer of the Bioliq process. Biomass can mean grass cuttings, straw waste, wood chips, food residue, etc. It is invariably moist and non-homogeneous, and it has a low energy density. As a result, the key step in the Bioliq process is pyrolytic densification to produce a high-energy syncrude for subsequent gasification.
Scientists at Evonik are taking a totally different approach. They want to use a mixture of syngas and ordinary glucose directly as a fermentation raw material. This idea is appealing, because it side-steps the cleaning and conversion stages. “Bio-organisms are not too particular when is comes to the purity of syngas,” explained Dr. Thomas Haas from Evonik. However, he admits that the yields are still two or three orders of magnitude short of what can be achieved with chemical catalysts.
Due to the difficulties involved, the processes used to produce syngas take up several pages in the standard technical chemistry texts. Ten different processes exist for coal gasification alone, which use a packed bed, a fluidized bed or an entrained-bed gasifier, but extremely elaborate equipment is needed, as the coal has to be finely ground at the start of the process. The output gas is contaminated with coal particles, and it has to be scrubbed prior to downstream processing. Dr. Otto Machhammer from the Process Development group at BASF is on solid ground with his estimation that “twice the specific investment is needed compared to syngas production because of the solids handling issue.”
Where Coal Gasification Makes Sense
Nevertheless there are countries where coal is so cheap that gasification is economically feasible. South Africa is often cited as an example, but China is following in South Africa’s footsteps and is exploiting its coal reserves to cover its need for basic chemicals and to reduce its dependency on oil exporters. China is using Fischer-Tropsch synthesis as well as the Lurgi MegaMethanol process which can be used to produce polypropylene directly from coal. When the contracts worth € 100 million were awarded in November 2006 for two projects covering the raw gas upgrading, methanol synthesis and methanol-to-propylene process phases, Lurgi Executive Board Chairman Klaus Moll proclaimed with great satisfaction that this signified the breakthrough in the industrial use of the new technology. Although syngas plays a major role in polypropylene production, plastic production volumes are still relatively modest. More than half of the gas is used to produce ammonia, followed by refinery hydrogen at 22 percent and methanol at 14 percent. Despite all of the hype about the coal-to-chemical strategy launched by the Chinese who would like to export the chemicals, people sometimes forget that natural gas is still the main input material for syngas. Natural gas is readily available, cheap, the equipment needs are reasonable and the technology has a proven track record. Steam reforming and partial oxidation or a combination of the two are the most commonly used processes at the present time.
Crucial Drawback: Cost Expensive And Large Plants
This is all mature, state-of-the-art technology, but there is a crucial drawback. The plants are very expensive, extremely large and as the reaction temperature is just under 1000 °C they consume large amounts of energy. At a recent Dechema Colloquium, Karsten Büker who works in the Research & Development Division at Uhde in Dortmund/Germany pointed out that multi-stand systems which supply 100,000 standard cubic meters of hydrogen per line are currently state-of-the-art in the industry. As a result, even very minor improvements can produce real cost savings. Process engineers are currently concentrating on catalysts which are more active and display less of a tendency to coking. To counteract the trend to even larger plants, Uhde has developed an autothermic methane reformer which does however require upstream air decomposition. Nevertheless, due to advantages of scale, the capital investment costs are lower compared to a steam reformer, emphasized Büker.
Udhe expanded its portfolio at the beginning of the year when it acquired RWE’s High-Temperature Winkler Process (HTW Process). Besides its Prenflow (pressurized entrained flow) process, the company can now offer an additional solids gasification technique which is particularly suited for lignite and bituminous coal that has a high ash melting point as well as for biomass such as wood, peat and even domestic waste. Karsten Radtke, who is in charge of the Uhde Gas Systems Business Unit believes that these input materials offer significant potential for the future.