The problem
In the 1980s the UK emitted over 3.75 million tonnes of sulphur into the atmosphere, of which approximately 70 per cent came from fossil fired power stations. The EC Large Combustion Plant Directive requires that SO2 emissions be reduced by 60 per cent from 1988 levels and thi4 must be achieved by the year 2003. The situation is similar in other European countries. This means that FGD equipment has to be fitted to many power stations; a typical installation is shown in Fig. 18.1. Some other countries in the world have previously been in the same situation themselves and results were not good. Enthusiastic promises and hurried technical choices were made, accompanied by ever-increasing bills, as electricity utilities embarked on large-scale FGD retrofit of their existing power stations. Then came the problems; many plants failed to meet their performance guarantees and could not remove enough SO2. Others either corroded badly or suffered process problems within the first 18 months of operation and some, sadly, did not work at all.
With hindsight, the problem with FGD projects divides into the following three parts.
Diverse technologies
There are many different FGD technologies - four major classes, each with eight or nine variants. Those with previous commercial application are owned by their licensors - large chemical engineering companies - whilst others exist only at the laboratory or pilot plant stage. The main FGD technology classes use different chemical reagents to remove the SO2 from the flue gas and produce different by-products. All make enthusiastic claims about their desulphurisation efficiency but the large number of technology variants, and different applications, makes them difficult to verify.
Case study task
This case study task is designed as a reporting exercise. The objective is to apply the FGD scenarios discussed in the text to the choice of FGD process design for a new 2000 MW coal-fired power station which is designed to burn 1.5% sulphur coal. The task is best addressed as a group exercise.
• First, read the case study text to get an overview of the FGD technologies and the principles of the total design approach.
• Discuss in groups the main issues of design choice. The group approach, whether arranged formally or informally, is the best way to gain the wide overall view required.
• Draft a short report explaining the main issues and drawing conclusions on the choice of FGD process. The report should follow the structure shown in Fig. 18.8 and be no longer than 750 words. Simple diagrams can be included if you feel they help explain things in a clear way.
The report content needs to be carefully chosen to suit the general readership mentioned in the case study text and include clear conclusions and recommendations. If it is necessary to divide responsibilities for sections of the report within the group, try to use the three elements of the total design approach discussed in the text: Engineering, Technology and Context.