问题 问答题

锅炉启动过程中如何控制汽包水位?

答案

参考答案:

锅炉启动过程中,应根据锅炉工况的变化控制调整汽包水位。

(1)点火初期,炉水逐渐受热、汽化、膨胀,使水位升高,此时应从定期排污门排出,既可提高炉水品质,又能促进水循环。

(2)随着汽压、汽温的升高,排汽量的增大,应根据汽包水位的变化趋势,及时补充

给水。在进行锅炉吹管或安全门校验时,常因蒸汽流量的突然增大,汽压突降而造成“虚假水位”现象。因此在进行上述操作前应保持较低水位,而后根据变化了的蒸汽流量加大给水,防止安全门回座等原因造成水位过低。

(3)根据锅炉负荷情况,及时进行给水泵切换,并根据规定的条件,投入给水自动装置。

单项选择题

It is clear that some chemicals can damage the health of animals and humans. (1) , this is not the only problem that (2) be caused by the careless use of chemicals. Chemicals can also (3) the ecological balance of the environment. If the ecological balance is disturbed, the results can be (4) serious.The (5) of DDT illustrates the problem. DDT, a chemical which kills insects, at first seemed to be a perfect answer (6) many problems. It would control insects that caused dangerous diseases, (7) insects that caused billions of dollars of damage to crops every year. Governments permitted and even (8) the use of DDT. Farmers in many countries (9) to spray it on their crops. The (10) results were good. Damage to crops (11) down, and profits went up. However, the chemical had effects which the scientists didn’t see in (12) . First, it also killed insects which were the (13) enemies of the harmful insects and which were therefore beneficial to farmers. Second, and perhaps worse, DDT did not kill (14) harmful insect. A few insects had natural resistance to the chemical. They (15) and reproduced in large numbers. In a few years there were large numbers of insects which were not (16) by DDT, and there were (17) insects which Could act as natural (18) on these new "super-insects". Finally, it became clear that DDT was not solving the insect problem. In fact, it was making the problem worse. It (19) became necessary to find a second (20) for the effects of the first.

 

第(9)空应选择()

A.wanted

B.began

C.decided

D.arranged

单项选择题 A1/A2型题