Proceedings of the Institution of Mechanical Engineers,Conference Proceedings

This paper traces the evolution of the high-pressure feed pump in this country over the last decade, concentrating on its application in land-based, steam power plant.

The influence of the choice of feed system and the effect of mounting feed water flow rates, pressure, and temperature on the design of the feed pump is discussed.

Advantages and disadvantages of the various methods of driving a feed pump are enumerated and attention given to the reasons for the adoption of higher running speeds, and the means whereby high-speed pumps have been accommodated in view of their higher net positive suction head requirements.

Material selection and component design is also considered in the light of the changing requirements brought about by larger size, more onerous operating conditions, and higher running speed. Glands, axial thrust balancing devices, impeller mountings, controls, and high-pressure joints, are each briefly discussed.

The plant features involved in the regulation of feed water on 500-MW units currently being installed by the C.E.G.B. are outlined and the control requirements relating to this regulation considered. Methods of meeting these requirements in the units to be installed at Fawley Generating Station are described and the operation of the control scheme during the start-up and shut-down of the unit is also covered.

The problems confronting the chemist in control of water treatment for an industrial boiler plant are very complex and dictated to a great extent by the pattern of plant operation. An interesting field of study is presented, particularly where the plant is modern in design and very extensive in the service it provides.

The author has concerned himself principally with the problems of water supply and treatment at Aylesford Mills, as these are very typical of those which occur in other large industrial undertakings.

Details are given of the feed water treatment plant for the medium- and high-pressure boilers, consisting of primary sedimentation units using lime, ferrous sulphate, and alum as chemical additives, followed by a filtration stage. This section of the plant is followed by a dual system comprising three base-exchange softener units and a fully automatic demineralization plant. The interesting features of fully automatic regeneration of the demineralization plant are discussed, together with the author's experience in operating this plant.

Emphasis is placed on high standards of feed water treatment and the principles of the system adopted. Sodium sulphite and tannin are added as chemical deoxidants on medium-pressure plant. Hydrazine, together with a neutralizing amine, are used on the high-pressure boiler installation.

The author concludes the paper with comments on the subject of boiler corrosion.

This paper is intended to be of a practical nature and deals with the various aspects and problems which require to be considered and dealt with by a project engineer responsible for the layout, design, and engineering of a main steam piping system.

Two types of installation are considered:

(a)

Main steam piping for power station plants operating within a temperature range of 482°C (900°F) and 568°C (1055°F), and

Although many of the problems are common to both types of installation such as pressure drops, terminal reactions on plant, expansion, layout, etc., these in both cases are discussed and procedures proposed for the preliminary and final stages of design, in order to arrive at a reliable and economic installation.

The necessity of preliminary and final detailed analysis is shown and the importance of considering the various types of supports, guides, and restraints in conjunction with this work.

Other features dealt with are the drainage of steam lines, cleanliness during erection, clean service conditions, lagging, and their contribution to satisfactory operation of the piping systems.

The paper deals with steam valves as installed at large modern power stations. The types of valves dealt with are stop valves and safety valves.

In considering the former category, reference is made to design principles and applicability as well as to mechanical and metallurgical factors affecting component design. The influence of quality control techniques and commissioning hazards are discussed.

Safety valve design considerations are referred to, as are aspects of performance and noise, and also possible design trends.

The authors review the operating experience of evaporators and de-aerators used in power stations of the South of Scotland Electricity Board over the last 45 years.

Water sources used and their effect on evaporators are covered, together with the purity of the water achieved and the requirements for the various generating cycles. The type of evaporators available) their steam heating supply and delivery of the purified water to the system is discussed, together with some of the problems.

A review of the de-aerators, their integration into the various feed cycles and heating supply arrangements is made. The level of de-aeration obtainable is considered. Operating problems, both on base load and on two shifting, are discussed especially in connection with oxygen content and metal pick-up in feed systems related to boiler corrosion.

Future possible operational requirements are outlined.

The paper is set in a background of boiler commissioning for customers in power generating, industrial, marine, petro-chemical and oil-refining companies in Britain and overseas.

Some of the problems encountered during the commissioning of a diversity of units employing solid fuel, oil fuels, naphtha, gas fuel firing, either singly or in combination, are discussed, and actual case histories detailed.

The paper embraces difficulties experienced with the ignition of fuels, the control of flame shape, air distribution to burners, layout of fuel supply lines, safety circuits, and the necessity for close collaboration between the customer and the designer during the tender and contract stages, in order to avoid loss of availability, resulting from delays in commissioning or subsequent damage to equipment.

The paper begins with a brief description of the principles of electrical precipitation and continues with a section on mechanical and electrical design which covers casings, collector systems, discharge systems, rapping systems, insulators, rectifiers both mechanical and static, ‘sectionalization’ of precipitators, hoppers, and automatic control. A third section on operation covers points to be observed during commissioning, bringing boilers on load, and action in case of faults. The final section on maintenance deals with temporary action for short shut-down periods to eliminate faults that have occurred in operation and with long-term maintenance during boiler outage periods.

The C.E.G.B. operates 230 power stations of various ages and output capacities representing a total capital investment of some £2400 million. The steam conditions, sizes of generating units, and complexity of the installed plant reflect the stage of technical development at the time of their construction. These factors influence the cost of production at individual stations as also do the nature and cost of fuel.

The economic level of maintenance at each station is thus dependent upon a number of factors and must generally be established locally. This places an obligation on the maintenance engineer to collect and consider economic, in addition to technical, data. Also, service experience must be fed back to the design engineer so that future plant designs may be improved. Unless a simple and effective control system is employed paper work can become an intolerable burden.

Power station maintenance can be broadly divided between:

(1)

work which can only be carried out while a generating unit is shut down;

The first category has received the greatest attention, since the cost of keeping a modern generator out of service can be substantial. Planning of this work is based on Critical Path Analysis techniques which are now well known and widely practised.

However, the day-to-day maintenance of a large variety of auxiliary plant also presents a heavy planning burden upon the maintenance department. The basic minimum requirements for the effective local control of this work have been examined, while the most economic methods of:

(a)

co-ordinating maintenance in a number of stations in the best national interest, and

are also receiving attention.