• Boiler specification and purchase are very important functions as the life of a boiler plant exceeds 30 years. Proper purchase can save huge amounts in capital and run­ning expenditure and an error can be disastrous.

• Because a boiler is a customized item, it costs a lot of time and effort for the boil­ermaker to prepare a bid and an equal effort by the customer for evaluation. The efforts can be saved if the specification is prepared carefully and the evaluation is done efficiently.

• It is normal to advise the bidders of the evaluation terms at the time of bidding so that the proposals received are responsive and tailored for compliance.

The two most important parameters for evaluation are

1. Efficiency

2. Auxiliary power consumption

The cost of fuel and the regime of interest rates govern loading factors. Higher fuel and interest costs demand greater efficiency that justifies the additional cost via a faster return on investment. The following points should be considered in evaluating boilers:

• The first step is a careful analysis of the plant requirement under all conditions of operation, at both full and part loads. A proper set of specifications is required and only thereafter are bids requested.

• A request for quotation must include parameters for evaluation and the cor­responding loading factors, to enable the bidders to understand the operating philosophy and respond in the most appropriate manner.

• The specification must clearly state what parameters must be met without fail and what items may be customized. What are the criteria for rejection of bid or award of contract?

On receipt of bids at the buyer’s office a comparison must align the bids with the specifi­cations. Usually this involves detailed technical discussions. Only then can the bid evalu­ation take place. A typical basis for bid evaluation considers these points:

• A plant has to be designed for the best efficiency and the least auxiliary power.

• Of 8760 h in a year it is reasonable to assume that the plant would operate for 8000 h, after accounting for statutory shutdowns and maintenance. The plant would oper­ate at —85% of the rated load on an average. Alternately, it is even better to calculate the number of hours for each load at which the plant would be operating.

• Estimated running of plant on each fuel and the realistic landed cost of fuel should be noted.

• If a plant is expected to operate at part loads for longer times the part load per­formance data are to be obtained from the boilermaker and evaluation worked out suitably. This is because the part load performance varies among boilers and technologies. For example, the part load performance of a BFBC is significantly lower than that of CFBC or PF and one may erroneously opt for BFBC based only on full-load performance.

• Auxiliary power for boiler normally takes into account only the fan power as the feed station is part of the turbine island in power plants.

• Since the auxiliary power of the total power plant has to be minimized, loading factors for pressure drops across the SH and RH must be specified upfront to the boilermaker.

• All loading factors address the performance and not the build quality. Loading for nonavailability of the boiler, after factoring into account the statutory shutdown and any other forced major conditions, is sometimes done to enhance the reliabil­ity factor.

The evaluation process consists of calculating the annual fuel and power consumptions of the various bids for the specified number of operating hours and converting them into monetary values based on the given costs. The bid with the least operating costs is the one to be selected. Alternatively the differential cost on any base bid can also be worked out and loaded on the other bids. Boilers, particularly the medium and larger ones, are tailor-made and the evaluation factors promote a greater level of customization to meet specific needs.