Focused Practice

I. Answer the following questions:

1. What kind of drives has the market seen an increase in?

2. What is becoming more widespread along with permanent magnet synchronous motor drives and variations of reluctance motor drives?

3. Who will intelligent control techniques find widespread applications with?

4. What could be the next major breakthrough?

5. What continues to take a considerable share of the variable-speed market?

6. How much has the power circuit of the general industrial DC drive changed?

7. Why does the induction motor remain the industry workhorse?

II. Analyse the grammar structures underlined in the above text.

III. Speak on: DC drives.

Unit 27 Grammar: The Participle. The Gerund. The Infinitive Word List:

1. superheated steam	перегретый пар
2. purity	чистота
3. impurety	примесь, загрязнение
4. precipitation	осаждение
5. steam path components	составные части по пути прохождения пара
6. HP/IP/LP turbine (High/Intermediate/Low pressure turbine)	ступени высокого/среднего/низкого давления турбины
7. LP steam chemistry	химический состав пара низкого давления
8. boiler water	котловая вода
9. feed water	питательная вода котла
10. fossil power plant	электростация на ископаемом (органическом) топливе
11. molecular species	включения на уровне молекул
12. solubty	растворимость
13. volatility	летучесть, испаряемость
14. the condensate part	выпадающая в осадок часть
15. blade	лопасть турбины
16. deposit, deposition to deposit	отложение, осадок, осаждение; выпадать в осадок
17. ingress	вход, попадание
18. condenser	конденсатор
19. make-up demineralizer	очиститель добавочной воды от минеральных солей
20. evaporator	испаритель
21. condensate polisher	очиститель от осаждений
22. condensate polisher effluent contamination	загрязнение за счёт вытекающего потока из очистителя осаждений
23. underway	в процессе разработки
24. to date	на сегодняшний день
25. cycle chemistry	водно-химический цикл
26. ionic contaminant	ионная примесь
27. consistent (with)	совместимый (с)
28. tolerable	приемлемый

Steam Chemistry and the Turbine

Superheated steam entering a turbine typically contains low levels of impurities. As the steam expands through a turbine, the subsequent precipitation of impurities onto the surfaces of steam path components leads to a variety of problems in the HP, IP or LP turbine. Thus, the purity of boiler water, feedwater and steam are some of the most important criteria for ensuring the availability and reliability of components in fossil and nuclear power plants.

Of the highest importance for power plant operators is determining the allowable concentrations of molecular species often present in turbine steam, moisture, and deposits.

Further, current operating limits for steam and boiler water are derived from the equilibrium solubilities and volatilities of single compounds while multicomponent mixtures and rapid boiling and steam expansion exits in the steam cycle.

Contaminants such as chlorides, sulfates, organics, and carbon dioxide, enter the condensate part of the cycle, but do their damage in the boiler (tube failures) or in the turbine (blade and disc failures, and deposition). Sources for such impurity ingress into the steam and/or water process cycle include: (i) condenser cooling water in-leakage, or (ii) make-up demineralizer, evaporator or condensate polisher effluent contamination. C3orrosion products are generated in feedwater heaters and condensers and flow into the turbine where they deposit.

Work currently underway shows promise that a fully predictive model will soon be available to calculate steam composition from boiler water composition and to predict moisture composition from LP steam chemistry.

Chemical compounds are soluble in superheated steam, and their solubility sharply decreases as the steam expands.

To date the basis for deriving cycle chemistry guidelines has been: “Limiting the concentration of ionic contaminants throughout the plant cycle to levels consistent with steam impurity levels tolerable in the turbine will adequately protect the boiler and other cycle components”.