问题 问答题 简答题

大功率机组冷态启动时控制胀差什么指标,可采取哪些措施?

答案

参考答案:

冷态启动时主要矛盾是控制高压(中压)缸差的正值,防止其过大并可采取以下措施;

⑴合理使用汽缸辅助加热装置,使汽缸的绝对膨胀增加,使其和转子的膨胀相适应。

⑵缩短冲转前轴封供气时间,在保证真空提升的需要的前提下,最好能控制为20~30min以内,并采用低温轴封汽源。

⑶控制好温升速度和升速,加负荷速度,使机组均匀受热,延长中速暖机时间。

⑷采用有利于减少高压胀差的暖机方式。

⑸接带负荷后若高中压缸胀差偏大,还可采用中断双层缸间夹层冷却气流方式。

⑹为防止低压缸胀差过大,可适当提升排气温度。

阅读理解

阅读理解。

     LONDON ( Reuters) -Ecotourism (生态旅游) is  causing  a  lot

of damage to wildlife and may be endangering the survival(生存) of

the very animals people are flocking to see,according to researchers.

        Biologists and conservationists (自然环境持论者) are worried

because polar bears,dolphins, penguins and other creatures are

getting stressed and losing weight and some are dying.

       "Evidence (证据) is growing that many animals do not react

well to tourists in their backyard,"New Scientist Magazine said.

      The immediate effects researchers have noticed are changes in

behavior,heart rates,or stress hormone levels but they fear it could

get much worse and over the long term" could endanger the survival

of the very wildlife they want to see. "

      Although money produced through ecotourism,which has been

growing at about 10 - 30 percent a year,has major benefits for poor

countries and people living in rural areas,the Swiss-based World

Conservation Union(IUCN) and some govemments fear not all projects

are audited (审查) and based on environmentally friendly policies,

according to the magazine.

      "Transmission (传播) of disease to wildlife,or small changes

to wildlife health through disturbance of daily life or increased

stress levels,while not obvious to the casual observer,may translate

to lower survival and breeding," said Philip Seddon,of the University

of Otago in Dunedin,New Zealand.

    Scientists have noticed that bottle-neck dolphins along the

northeastern coast of New Zealand become nervously excited when

tourist boats arrive. Similar changes in behavior have been observed

in polar bears and yellow-eyed penguins in areas visited by ecotourists

that are producing smaller babies.

   Conservationists are now calling for more research into the

effect of ecotourism on animals and say the industry must be developed

carefully, They also want studies done before new ecotourism

projects are started.

      "The animals' welfare should be very important because without

them there will be no ecotourism," said Rochelle Constantine of

the University of Auckland in New Zealand.

1. What's the theme of the text?     

A. Many animals are dying for lack of money.

B. There will be no ecotourism without animals.

C. Ecotourism could endanger the survival of the wildlife people want to see.

D. More research should be done on ecotourism.

2. We may learn from the text that ____  .   

A. ecotourism must be developed properly

B. polar bears are losing weight without enough food

C. all the poor countries have stopped ecotourism

D. money produced through ecotourism should be spent on wild life

3. Which of the following is NOT mentioned in the text?  

A. Many animals do not react well in their backyard.

B. Polar bears in areas visited by ecotourists are producing smaller babies.

C. Ecotourism has been growing at about 10 - 30 percent ayear.

D. Studies should be done before new ecotourism projects are started.

4. What Rochelle Constantine said in the last paragraph implies  that____.

A. if people want to get high income,they must develop ecotourism

B. animals have rights to live their own life

C. animals are people's good friends

D. people should take good care of wildlife

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