问题 问答题 简答题

对制粉系统运行有何基本要求?

答案

参考答案:

锅炉对制粉系统运行的要求主要是:

1、出力:磨煤机总出力应满足机组目标负荷要求。

2、煤粉细度:煤粉细度直接影响磨煤机出力、燃烧效率和制粉系统功耗。因此存在一经济细度。制粉系统输出的煤粉细度应接近经济细度。

3、煤粉浓度:煤粉浓度与输送煤粉的一次风量密切相关,在出力一定的情况下,煤粉浓度依靠一次风量来控制。风煤比必须满足最佳状态(即与煤粉中挥发份组织燃烧所需的燃烧空气量大体接近)并避免处于0.3~0.6(煤/风)之间的爆燃区域。同时一次风量应避免煤粉在煤粉管道中的沉积。

4、煤粉气流温度:磨煤机出口煤粉温度决定于煤粉气流的着火稳定性和煤粉系统产生爆燃危险性之间的平衡

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Eight-year-old Jesse Arbogast was playing in the sea late one evening in July when a 7-foot bull shark attacked him and tore off his arm. Jesse’s uncle jumped into the sea and dragged the boy to shore. The boy was not breathing. His aunt gave him mouth-to-mouth resuscitation(人工呼吸) while his uncle rang the emergency services. Pretty soon, a helicopter arrived and flew the boy to hospital. It was a much quicker journey than the journey by road.

Jesse’s uncle, Vance Folsenzier, ran back into the sea and found the shark that had attacked his nephew. He picked the shark up and threw it onto the beach. A coastguard shot the fish four times and although this did not kill it, the shark’s jaws relaxed so that they could open them, and reach down into its stomach, and pull out the boys’ arm.

At the Baptist Hospital in Pensacola, Dr Ian Rogers spent eleven hours reattaching Jesse’s arm. “It was a complicated operation,” he said, “but we were lucky. If the arm hadn’t been recovered in time, we wouldn’t have been able to do the operation at all. What I mean is that if they hadn’t found the shark, we wouldn’t have had a chance.”

According to the local park ranger Jack Tomosvic, shark attacks are not that common. “Jesse was just unlucky,” he says, “evening is the shark’s feeding time. And Jesse was in an area without lifeguards. This would never have happened if he had been in an area where swimming is allowed.”

When reporters asked Jesse’s uncle how he had had the courage to fight against a shark, he replied, “I was mad and you do some strange things when you’re mad.”

小题1:What was the boy doing when the accident happened?

A.Feeding a hungry shark.

B.Jumping into the rough sea.

C.Dragging a boy to the shore.

D.Swimming in a dangerous area.小题2: In which way did the boy’s uncle help with the operation?

A.By finding his lost arm.

B.By making a phone call.

C.By flying him to hospital.

D.By blowing into his mouth.小题3:How was his uncle in time of danger?

A.Careful.

B.Brave.

C.Optimistic.

D.Patient.小题4:According to Jack Tomosvic, _______.

A.people are often attacked by sharks

B.sharks never attack people

C.Jesse was unlucky to have been attacked by a shark

D.Jesse was swimming in a safe area at the moment