Coal Impact Assessment For Advanced Power Generation Technologies

Environmental pressure on coal based power generation has lead to the development of a number of new technologies which offer superior environmental performance over conventional pulverised coal fired power generation. Of these technologies Integrated Gasification Combined Cycle (IGCC) is expected to represent a significant proportion of new coal fired capacity to be installed over the next decade. As IGCC technology is still in its infancy there is little public data on the performance of coals in these plants. The objective of the project is to develop within Australia expertise in IGCC technology and the capability to test and independently assess coals and their interaction with three generic IGCC processes from technical and economic viewpoints.

The project conducted a technical and economic assessment of six selected export coals in three Integrated Gasification Combined Cycle processes. The assessment was conducted through a combination of laboratory testing and computer simulation covering three major project areas:

1. Assessment of high pressure coal gasification reactivity.
2. Integrated Gasification Combined Cycle process simulation.
3. Evaluation of relative coal utilisation costs using a Coal Value Model approach.

The IGCC processes considered are the most advanced gasifier designs for high rank coals: oxygen blown dry feed (Shell), oxygen blown slurry feed (Texaco) and air blown dry feed (Mitsubishi Heavy Industries).

A methodology and assessment tools were developed to enable the independent assessment of the performance of coals in IGCC processes.

The laboratory testing of the coals under gasification conditions demonstrated that the production of coal chars and subsequent measurement of char reactivity under high pressure conditions requires considerable expertise, close attention to experimental technique and specialised equipment. Char reactivities as determined for the six coals varied by up to 500%. The Integrated Gasification Combined Cycle process simulation work yielded mass flows and process efficiencies for the six coals in the three IGCC processes. The overall cycle efficiencies ranged from 41.1% to 42.8% for the Shell process, 39.2% to 40.4% for the Texaco process and 42.2% to 43.8% for the MHI process. The relative utilisation costs of the six coals was found to vary by up to $5 per tonne of coal.

Coal properties were found to influence a number of facets of IGCC plant performance and to potentially have a significant impact on the overall coal utilisation cost. These facets include the overall cycle efficiency, oxygen usage and flux requirements. Assessment of coal impact on plant performance requires a holistic approach which allows these impacts to all be considered.

Desirable coal properties for Integrated Gasification Combined Cycle plants include:

• low moisture
• low ash content
• high rank
• low ash fusion temperatures
• high char reactivity
• low sulphur
• high HGI

The coals considered had predicted utilisation costs which differed by up to $5 / tonne coal.

The relative utilisation costs of the six coals varied between the three processes. Knowledge of the IGCC process is therefore necessary for accurate impact assessment.