• static gas side pressure drop
  • steam flow – nominal, maximum, and required steam turndown
  • steam temperature
  • steam pressure at the header
  • expected cycling operation of the HRSG
  • is a bypass system required for the gas turbine to operate in simple-cycle duty?
  • emissions limits
  • noise limits from – the casing, safety relief valves, and steam vents
  • required response of the HRSG when there are variations in steam header pressure from:
    – changes in steam demand
    – loss of steam supply from another source
  • is fresh air firing required?
    – forced draught (draft)
    – induced draught
  • steam demand that requires supplemental firing when the gas turbine is operated at part load.
Liners can become oxidized once the material temperature limits are exceeded
They can be severely deformed with high temperatures and poor liner support


With this information from the customer, HRSG designers can apply their design rules to develop an HRSG system design that meets all the requirements.

The starting point in the design of all HRSGs is determining the optimum heat transfer surface area required to meet the steam requirements and the gas side static pressure drop. As well as sizing the surface area, the designer also needs to select appropriate tube, header and piping materials based on the pressures and temperatures that they will be exposed to. Table 1 lists some of the typical tube materials used in a HRSG together with typical locations.

Selecting the appropriate material is not as easy as it first looks

Unfortunately, selecting the appropriate material is not as easy as it first looks. In addition to the pressures and temperatures the tube materials will be exposed to, designers also need to take into account the potential for corrosion due to condensation from water condensing on the outside surfaces. In the case of oil firing, there is also the problem of acid condensing on the outside tube surfaces. There is also the issue of flow-assisted corrosion in certain areas of the HRSG. In all cases, the appropriate selection of materials will minimize the loss of tube material.

opportunities in central and eastern Europe

Energy intensity tends to be very poor in countries where the EBRD is active, suggesting there ought to be scope for investment in new, more efficient cogeneration technologies. And so there is, writes Peter Hobson, but developers also need to understand some complex structural issues.

The European Bank for Reconstruction and Development (EBRD) invests in the former command economies of central, eastern and southern Europe, the Caucasus, Russia and central Asia. The 27 countries cover an area ranging from the European Union in the west to within a few miles of Japan in the east. The most northern parts are permanently frozen while the most southern countries enjoy a Mediterranean climate. Political and ethnic diversity in this huge region of 400 million people is just as complex. Not surprisingly, the energy needs in these countries, mostly industrialized, are formidable. According to the IEA, the region as a whole in 2002 accounted for nearly 12% of global energy consumption – from a population of around 7% of the entire planet – so energy intensity is very high. But this is not the full story.

The energy infrastructure in the EBRD ‘region’ is fundamentally different from anywhere else. There are two main reasons for this. The first is that in Soviet times, energy was provided as a practically free commodity on the basis that the more you used, the more you produced. As a consequence, industrial infrastructure was built to use as much energy as possible. There have been huge improvements over the last decade, particularly in those countries that recently joined the EU; however, many countries still have a long way to go, and the region as a whole lags behind its western neighbours. The other reason is district heating. This was central planners’ favoured method to provide heating for residents living in densely populated, high-rise block housing. The need for large-scale heat production has had an impact on the power sector, in which there is widespread use of large-scale cogeneration plants.

In Soviet times, industrial infrastructure was built to use as much energy as possible

Much of the industrial and heating infrastructure was built years ago and is now old and inefficient. Exact figures are hard to come by, but based on available evidence and with what you can see with your own eyes, this region is clearly a land of opportunity for the cogeneration industry .Evidence for this is provided in Figure 1, which compares energy intensity and carbon intensity of EBRD countries with those of the EU, US and OECD.