Chemical Equipment Update

Careful planning for problem-free operation

Paul Köberlein investigates avoidable loads on shell steam boiler systems

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team boiler systems are subject to various types of loading which can lead to varying degrees of stress on the boiler body. In addition to inadequate water quality, two main factors are of essential importance: the effects of design

and settings and the effects of consumers. The following article describes the avoidable loads on boiler systems and provides the reader with an insight into the proper planning, construction and setting of systems right through to operation. Saturated steam is used today as a heat-carrying medium in

many different commercial and industrial companies in every sector of industry. In the food and beverage industry, heating, boiling and cleaning processes are supported, the textile industry uses the heat medium primarily for the further processing and finishing of fabrics, laundries and dry cleaners heat up washing machines or use the steam for smoothing and drying processes. In hospitals, ultra-clean steam is used to sterilise operating equipment, and steam supplies the adjoining large-scale kitchens or is used for humidification of the air conditioning system. The building materials industry needs saturated steam for many process, heating and drying procedures, such as the autoclaving of sand-limestone bricks. And in many other sectors, such as the chemical industry, pharmaceuticals and many more, steam is essential as a heat medium. Most of these steam applications require saturated steam

or slightly overheated steam with outputs of up to 200t/h, pressures up to 30bar and steam temperatures up to 300°C. For

generating steam, one or more gas- or oil-fired steam boilers is generally used in the structure as a shell boiler (Fig. 1). In comparison to water pipe boiler systems these are by far the better alternative, in the relevant performance range, because they are cheaper to buy and to run. Operating modern shell steam boiler systems is regarded as

unproblematic nowadays. Nonetheless, these boilers are often subject to a series of problems – which are actually avoidable – which have a major influence on the safety and working life of these energy generators. In addition to inadequate water quality, two main factors are of essential importance: the effects of design and settings and the effects of consumers Inadequate water quality, resulting in corrosion or the

formation of deposits, is top of the list in the damage statistics. The results of this type of damage are generally known in the industry, and will therefore not be discussed in greater detail in this specialist report. Poor water quality is often caused by one or all of the following: insufficient monitoring or testing of the necessary water parameters (Fig. 2); lack of expertise; and misinterpretation of measured values or no reaction in the event of deviations. To avoid damage resulting from insufficient water quality,

first of all, compliance with the water values specified by the water manufacturer (according to EN 12953 Part 10) is essential. In addition to using suitable water treatment components, attention must also be paid here to ensuring sufficient competence in the field of water analysis. It is recommend that fully automated analysis devices are installed, which will record and monitor all water parameters such as hardness, conductivity, pH and condensate purity (Fig. 3)..

Effects of design and settings

The of boiler output too high in relation to the steam output actually needed problem is often to be found in systems in which the steam consumption has been dramatically reduced through the loss of consumers or the subsequent use of any heat recovery potential that is available. But new systems can also be affected if, during planning, the simultaneity factors of the consumers were incorrectly evaluated or were calculated with excessively generous output reserves. The consequence of a steam take-off that is too low in relation to the boiler output is frequent switching on and off of the burner. This causes temperature changes that can be extreme, especially in the case of gas-fired boiler systems and long preventilation times. Burners create temperatures between 1400 and 1700°C in

Fig. 1. A Loos International shell boiler in an industrial company.

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the furnace. During the furnace preventilation phase, which is prescribed before each burner ignition process, fresh air in taken in out of the boiler house. The low air temperatures of 20-30°C cause the previously hot heating surfaces to cool down. After Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44