Steam chemistry

Water Treatment. Water and steam chemistry must be rigorously controlled to prevent deposition of impurities and corrosion of the steam cycle. Deposition on boiler tubing walls reduces heat transfer and can lead to overheating, creep, and eventual failure. Additionally, corrosion can develop under the deposits and lead to failure. If steam is used for chemical processes or as a heat-transfer medium for food and pharmaceutical preparation there are limitations on the additives that may be used. Steam purity requirements set the allowable impurity concentrations for the rest of most cycles. Once contaminants enter the steam, there is no practical way to remove them. Thus all purification must be carried out in the boiler or preboiler part of the cycle. The principal exception is in the case of nuclear steam generators, which require very pure water. These tend to provide steam that is considerably lower in most impurities than the turbine requires. A variety of water treatments are summarized in Table 5. Although the subtieties of water treatment in steam systems are beyond the scope of this article, uses of various additives maybe summarized as follows ... 

In typical cause-and-effect fashion, these particular problems stem from less than satisfactory boiler waterside conditions and have their origins in any of several, often interrelated, mechanical, operational, or water-steam chemistry irregularities. 

Also, the particular boiler plant water-steam chemistries must be reviewed and interpreted at regular intervals. The specifics and complexity of this work depend on the type of boiler plant involved and the respective chemical treatment programs employed. The frequency of testing may range from hourly to perhaps monthly, again depending on the type of boiler operation. 

D Amore, F. Truesdell, A. H. 1979. Models for steam chemistry at Larderello and the Geysers. In Proceedings 5th Stanford Geothermal Engineering Workshop, Stanford, 283-297. 

This chapter was developed as part of the Hubbard Brook Research Foundation Science-Links program funded by Jessie B. Cox Charitable Trust, Davis Conservation Foundation, Geraldine R. Dodge Foundation, McCabe Environmental Fund, Merck Family Fund, John Merck Fund, Harold Whitworth Pierce Charitable Trust, the Sudbury Foundation, and the Switzer Environmental Leadership Fund of the New Hampshire Charitable Foundation. Support was also provided by the W. M. Keck Foundation and the National Science Foundation. We are indebted to Gene Likens for the use of long-term precipitation and steam chemistry data at Hubbard Brook. This is a contribution of the Hubbard Brook Ecosystem Study. 

In the VVER plants the steam generator water has to fulfil various purity requirements such as low conductivity and low dissolved oxygen, with the pH being 7 or somewhat less. As far as it is known, no additives are used in order to control steam generator water and main steam chemistry. 

IS] Jonas, O. and Dooley, B., Steam Chemistry and its Effects on Turbine Deposits and Corrosion, 57th International Water Conference, Pittsburgh, October 1996. 

Table 8.11 Monitoring Reiated to Water and Steam Chemistry, Scaie, and Deposits [17]...

It should be emphasised that all the processes here described are considered essentially from the practical standpoint. The student should always acquaint himself with the theoretical basis of these operations, for which he should consult any standard text-book of physical chemistry this applies particularly to such processes as the distillation of constant boiling-point mixtures, steam-distillation, ether extraction, etc. 

The BWR water chemistry parameters are given in Table 4 (19). Originally, no additives were made to feedwater—condensate or the primary water. The radiolytic decomposition of the fluid produced varying concentrations of O2 in the reactor vessel, ranging from about 200 ppb O2 in the reactor recirculation water to about 20 ppm O2 in the steam. Stoichiometric amounts of hydrogen were also produced, ie, 2 mL for each mL of O2. Feedwater O2 was about 30 ppb, hence the radiolytic decomposition of the water was a primary factor in determining the behavior of materials in the primary system and feedwater systems. 

Solubility. An important aspect of sihca chemistry concerns the sihca— water system. The interaction of the various forms of sihca with water has geological significance and is apphed in steam-power engineering where the volatilization of sihca and its deposition on turbine blades may occur (see Power generation), in the production of synthetic quartz crystals by hydrothermal processes (qv), and in the preparation of commercially important soluble sihcates, coUoidal sihca, and sihca gel. 

There is a close kinship between the chemical process industry and the nuclear electric power industry. In tact once the physics of nuclear reaction was established the rest is chemistiy and hc.it ii an.sfer. The word "reactor" is from chemistry for the location the reaction takes place.. nuclear reactor consists of a vessel in which a nuclear reaction heats water to make steam to drive a turbine o generate electricity. Thus the primary components are pipes, valves, pumps heat exchangers, and water purifiers similar to the components found in a chemical plant. Following the success of WASH-1400, PSA was used to analyze the chemical proce.ssmg of nuclear fuel and. aste preparation for disposal. 

When dealing with a large steam plant, the chemistry and the methods of water treatment required are complex. 

Chemistry of Petrochemical Processes Steam/Hydrocarbon Ratio... 

Baum, A., Water chemistry and corrosion in the steam/water loops of nuclear power stations Seillac, France, Mar. 1980 (1980)... 

Klein, H. A., Corrosion of Fossil Fuelled Steam Generators , Conference on Water Chemistry and Aqueous Corrosion of Steam Generators, Ermenonville, France (1972)... 

It has been known for centuries that codistillation of many plant materials with steam produces a fragrant mixture of liquids called essential oils. For hundreds of years, such plant extracts have been used as medicines, spices, and perfumes. The investigation of essential oils also played a major role in the emergence of organic chemistry as a science during the 19th century. 

Steam-Moderated Process. The basic idea behind this approach is to limit the extent of conversion of the methanation reaction, Reaction 1, by adding steam to the feed gases. This process simultaneously provides for (46) elimination of the CO shift, Reaction 2, to get a 3 1 H2 CO ratio from the make-up gas ratio of about 1.5 1 and avoidance of carbon laydown by operation under conditions in which carbon is not a thermodynamically stable phase (see Chemistry and Thermodynamics section above). 

In the following pages I have endeavoured to deduce the principles of Thermodynamics in the simplest possible manner from the two fundamental laws, and to illustrate their applicability by means of a selection of examples. In making the latter, I have had in view more especially the requirements of students of Physical Chemistry, t6 whom the work is addressed. For this reason chemical problems receive the main consideration, and other branches are either treated briefly, or (as in the case of the technical application to steam and internal combustion engines, the theories of radiation, elasticity, etc.) are not included at all. 

Low-pressure steam-generating Cl models are particularly sensitive to changes in water chemistry, and their rough waterside surfaces makes them susceptible to deposition, and thus to the risk of overheating and subsequent cracking. Typically, they are quite small boilers, most being less than 200 hp. 

NOTE As a consequence of the different kinds of operational and management problems associated with raising steam in industrial boiler plants, it often requires a different mindset than that needed for a base-load utility power house, where personnel strive to maintain steady-state (but knife-edge) operating conditions. The differences between industrial plants and power generators is also reflected in the waterside chemistries and monitoring and control objectives of their respective boiler plant systems. 

THE SCOPE OF BW TREATMENT AND CONTROL OF STEAM/WATERSIDE CHEMISTRY... 

The control of steam-water and internal surfaces chemistry within closely defined parameters... 

---