问题 问答题 简答题

试述给水中加联胺的目的、原理?

答案

参考答案:

给水中加联胺的目的是为了降低除氧器出口水的残余溶氧。

加联胺的作用原理:联胺是一种还原剂,特别是在碱性溶液中,它是一种很强的还原剂,可将水中的溶氧还原。

反应式如下:

反应产物N2和H2O对热力系统的运行没有任何害处;在高温(t>200℃)水中N2H4可将Fe2O3还原成Fe3O4以至于Fe,N2H4还能将CuO还原成Cu2O或Cu,联胺的这些性质可以用来防止结铁垢和铜垢。

单项选择题
完形填空

Section C

Directions: Read the following passage and choose the most suitable heading from A-F for each paragraph.  There is one extra heading which you do not need.

(D)

A. Value of rare skills

B. Dangerous jobs paid more

C. Social demand decides reward

D. Developing skills

E. Women’s skills rewarded

F. Reason for taking low-paying jobs

1. _________________________

The rewards of a skill that is in strictly limited supply depend upon the demand for that skill. Men’s professional basketball is extremely popular, and the top NBA players make millions of dollars per year. There are some great women basketball players, too, but because women’s professional basketball has not become popular, these women’s skills go comparatively unrewarded.

2. _________________________

Some people with very rare skills can make enormous salaries in a free market economy. Paula Abdel has a voice that millions of people are willing to pay to hear in person, and on tapes, CDs, records, and videos. Before Pablo Picasso died, he could sell small sketches for vast sums of money. Were they worth it? They were worth exactly what the highest bidder (出价人) was willing to pay.

3. _________________________

Not all skills are inborn, however. Some people have invested in training and schooling to improve their knowledge and skills. When we go to school, we are investing in human capital that we expect to yield dividends, partly in the form of higher wages, later on. Human capital is also produced through on-the-job training.

4. _________________________

Some jobs are more desirable than others. Entry-level positions in attractive industries such as publishing and television tend to be low-paying. Since talented people are willing to take entry-level jobs in these industries at salaries below what they could earn in other occupations, there must be other, non-wage rewards. It may be that the job itself is more personally rewarding, or that a low-paying apprenticeship is the only way to acquire the human capital necessary to advance.

5. _________________________

On the other hand, compensating differentials are required when an occupation is very dangerous. Workers on skyscrapers and bridges command additional wages. Fire fighters in cities that have many old, run-down buildings are usually paid more than those in relatively tranquil rural or suburban areas.

SectionD

Directions: Read the passage carefully. Then answer the questions or complete the statements in the fewest possible words.