It was gratifying to see that the Chinese government has taken its pollution issue so seriously. In its 13th 5 Year Plan (2016 to 2020), China intends to achieve an electrical mix that includes 20 per cent “Non-Fossil Fuel” with an overall target of emitting less than 550g CO2 per kWh of electricity produced. The cynical will see that their categorisation as non-fossil, would catch everything including hydro and nuclear, so the 20 per cent target is perhaps not as meaningful as it could be. However, the same 5 Year Plan targets 50 per cent non-fossil fuel by 2050, and whilst this might be a long time in the future, this is a very meaningful number that will require biomass in the mix in a serious way.
The electrical capacity in China is currently 1650GW, of which biomass currently makes up 0.7 per cent (12GW), so lots of room to grow. At a 25 per cent co-firing rate (a high-side number), this could become 275GW for example. Coal is used to fuel about 1,100GW of the national grid. The 5 Year Plan also contemplates running about 100 demonstration plants to kick off the co-firing of biomass. Some of these have already started.
As the discussions and presentations took place, it was clear that wood pellets were the best technical and logistical biomass option. However, the subject is politically sensitive. The issue in China today is that they claim that a significant portion of their particulate pollution comes from farmers burning their stover/stalks after harvesting. Therefore, the Chinese government is trying to kill two birds with one stone by co-firing these agricultural residues to both lift the Chinese non-fossil percentage, whilst simultaneously addressing the farmers’ pollution problem. A beneficial side effect of this strategy is that by providing farmers with another revenue stream (for their biomass), the government hopes to arrest the human migration from rural into urban areas. So the emphasis in China is currently on agricultural biomass. They believe that there are some one billion tons of the stuff available, which theoretically could fuel their entire electricity requirement. So another political objective is for the country to reduce its energy dependence on imports, which is already low in percentage terms.
On the technical front, there was consensus that direct co-firing of these agri residues would create slagging and fouling of the boiler tubes and associated de-rating of the boilers. The root cause of this ash deposition has been identified as high alkali elements (mainly potassium) combining with chlorine in the fly ash. Apparently this can be mitigated by the introduction of sulphur in the boiler. To avoid this issue altogether however, they are looking hard at first gasifying the biomass, then co-firing the gas indirectly.
In addition, there is the issue of logistics. A university study suggested that if every power plant were given a 50-kilometre collection radius around itself, it could secure enough agricultural biomass to co-fire at the required level, albeit seasonally. However, this would require the physical movement of huge amounts of biomass. The cutting and hauling requirement alone is daunting, never mind the storage required at either end.