Ask the Consultants

The Boyce Consultants offer a monthly article to answer the questions of their readers, for instance a sample follows:

Question: Under what circumstances should a plant look into the production of its own electrical power, and what benefits would the plant incur?. 

Answer:  The answer to this question is rather complex and will vary from plant to plant. The cost of production of electrical power is an important one but in no ways is it the deciding factor. The following are some of the critical points that one must look into to make an intelligent assessment of the problem: 

Total plant capacity 

Power usage profile on a daily, monthly and yearly basis. The flatter the profile the more economical will be the result.

Other sources of energy the plant utilizes. This could be based for example: upon the amount of steam utilized in various processes; to the direct heating of other process such as furnaces in Iron and Steel mills, heating consumption to raise the temperature of chemicals and other liquids in major chemical plants or refineries; or to the use of direct heat or steam in absorption units for cooling purposes. 

The history of the present supply of power, such as decrease in the voltage supply which could harm various electrical drives, or the reliability and security of supply to cause brownouts and blackouts, is a very important factor in determining the viability of such a project. Shortfalls in reliability are disastrous for many civil infrastructures, manufacturing processes, or health care facilities and in many cases can be the single most important point criterion in scoping alternative power sources. In suitable circumstances they can and would even transform what might appear at first sight to be an apparently expensive power generation into an excellent and highly cost effective project, which would be a financially palatable investment opportunity. 

The type of fuel available for generation of the power at the plant site is a very significant factor in the decision of incorporating a plant at any given location. Natural Gas is by far the best fuel to use for nearly any type of combustion based power plant, if it is available and competitively priced at the proposed plant location. Its availability should be well investigated, especially with reference as to its supply the all year round. Diesel fuel is a good alternative choice, and while it can produce the energy with only a minor reduction of plant life, again its supply and treatment requirements, as per its properties, must be well investigated. The use of dual fuel Prime Movers should also be investigated. The use of heavy fuels, though not the best from the machinery standpoint, in some circumstances could be justified especially if the history of power supply to the plant is full of brownouts and blackouts. 

The cost of maintaining an external power supply option also should o be investigated. This can reduce the need for unnecessary system redundancy. In some cases, excessive plant capacity can be a very expensive form of insurance. The proper use of multiple sizes and types of power generation equipment can reduce the cost of externally sourced power. Most of the externally sourced power supply costs are based on maximum power used at any one time (capacity charge). This charge is between 50-60% of the total charge per kW/h. This maximum power factor typically will penalize the plant for the year. 

It is important to remember that the cost of the new plant is only between 8-10 percent of the life cycle cost. Maintenance is about 15-20 percent of the life cycle cost and that fuel is about70 –80 percent of the life cycle cost. It is therefore very important to design a very efficient plant cycle with efficiencies at a minimum in the mid 40's. 

The move to "Inside The Fence" plants is growing throughout the world. These plants require careful study, evaluation, and design before any serious financial commitments can be made.