The purpose of the control is to keep the pressure upstream of the mill constant on a preset Set point level. The manipulated variable is in this case the position of the throttle valve in the return gas duct. Generally, a change in pressure is due to temperature control varying the fuel gas supply to the hot gas producer, with the consequence of a different hot gas volume being produced.
控制的目的是保持入磨前的风压稳定在一定的设定值。在这个控制回路中操作的变量是在循环风管的节流阀阀板的位置。通常，压力的变化是由于温度的控制改变了供给热风炉的燃气量，是改变了入磨的热风量的结果。
However, to ensure a uniform product quality, it is indispensable to operate the roller mill with a constant gas volume. This is achieved with a compensation of the varying hot gas volume by a corresponding return gas volume.
然而，为了保证稳定的产品质量，磨机在稳定的风量条件下操作是必不可少的。这可以通过用相应的循环风量补偿系统热风量达到系统的风量平衡。
3.4 Operation under extraordinary conditions 特别情况下的操作
3.4.1 Start-up of plant 系统启动
The start-up sequence of the individual components was already described under “3.2.1 Start-up sequence“. Generally, the philosophy applies to put the various control loops as early as possible in the automatic mode, in order to simplify the operator’s work and to save his attention for more important things.
单个设备的启动顺序已经在“3.2.1启动顺序”中介绍过了。一般来说，各个自动控制回路在自动模式下要尽可能的早投入使用， 此是为了简化操作者的工作使其更注意重要的事。
The raw material transport, the auxiliaries of the roller mill and the gas routes being in opera-tion, the mill must first be heated. To avoid mechanical damage, the temperature for heating up the mill must be limited to 250 °C at the roller mill inlet. Moreover, heating up should be made slowly. The heating up period is over as soon as a temperature of approx. 120 °C ex-ists downstream of the mill.
在系统操作中，喂料输送、立磨的附件设备及废气处理管道先被加热。为避免设备机械损坏，在立磨磨机进口加热磨机的温度限制值为250 °C。而且加热应缓慢进行。在加热期间磨机出口存在大约120 °C的温度。
Before starting the drive unit of the grinding table, the hydraulic system of the mill is set to 50 - 60 bar and the feed to 60 – 70% of the rated throughput. After starting the material feed, the mill fan is immediately accelerated to approx. ca. 80 – 85% of the rated speed.
在启动磨盘的驱动装置时，磨机液压系统设定至50- 60 bar和料通过量的60 – 70%的进料量。在启动喂料后，磨机风机立即加速至大约80 – 85%的速率。
Then, the operator must manually adjust the return air flap and the hot gas flap in order to ensure a sufficient negative pressure level upstream of the mill. But the pressure down-stream of the mill must not fall below 80 °C. Appro x. 1 minute after starting operation of the main drive unit, the working pressure is built up in the hydraulic system.
然后，操作者必须主要调整循环风阀门和热风阀门以确保磨机前有效的静压值。但是出磨后的风温必须不低于80 °C。在主马达启动后大约..1分钟，液压系统建立起了工作压力。
Mill operation being stable, operation of the controllers is started and the feed quantity in-
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creased in steps.
磨机的操作应保持稳定，控制（回路）器的操作投入使用，一步一步增加进料量。
3.4.2 Shutdown of plant 系统的停机
For a normal shutdown of the roller mill, the material feed is reduced in steps to approx. 60 -70% of the rated throughput. The return air flap and the hot gas flap must be adjusted ac-cordingly in order to avoid that the temperature downstream of the mill increases too much. 立磨正常停机时，进料量应逐步减至通过料量的大约60 -70%。循环风阀门和热风阀门应同时调整以避免出磨后风温增加的太快。
At the same time of interrupting material feed, operation of the main drive unit is stopped. Then, the speed of the mill fan must immediately be reduced to approx. 20%. Moreover, the hot gas flap must be closed as quickly as possible. The return air flap must be adjusted so that no overpressure is produced upstream of the mill.
中断进料的的同时，主马达停止。然后，磨机风机的转速必须降至20%。而热风风阀必须尽可能的迅速关闭。循环风阀门必须调整至入磨风无正压。
3.4.3 Operation with insufficient material quantity 不足料量的操作
If the mill is operated with an insufficient material quantity, the following displays in the con-trol panel inform accordingly:
如果磨机操作在不足料量的情况下，在控制台会出现以下相应的显示：
Displays: 显示
_ Stronger vibrations occur on the mill drive unit because, due to insufficient material feed, the material bed considerably decreases and the grinding rollers partly contact the table liners. Mill operation is stopped at a vibration level of more than 8 – 10 mm/s.
主马达传动装置上会有强烈的振动，由于不足的喂料量，料床会相应减少并且辊轮会部分的接触磨盘衬板。在振动值超过8 – 10 mm/s时磨机操作会被停止。
_ Decrease of the differential pressure of the mill is displayed in the control panel room. If the mill is operated with a differential pressure controller, the controller will automatically increase the material feed.
磨机压差的降低显示在中控室内。如果磨机操作是由压差控制器控制，则控制器会自动增加进料量。
Possible causes:可能的原因
_ Material feed insufficient or disturbed 进料量不足或者波动 _ Better grindability of the material feed 进料有更好的易磨性
_ Reduced number of material circuits inside the mill due to separator adjustment (towards coarser finished product) 由于选粉机的调整，磨机内料循环的次数减少(产品变粗)
3.4.4 Overfilling of mill 磨机过量进料
In case of overfilling of the mill, the displays inform as follows: 若发生磨机过量进料，会有如下之显示：
_ Strong vibrations occur on the mill drive unit because the higher material bed can produce a super proportional increase of the material bed depth which entails a higher rolling resistance of the grinding rollers. This also raises the specific energy consumption for the grinding process.
主马达传动装置上会有强烈的振动是由料床增厚磨内料量增加而引起。增加的料床高度需要更高的碾磨阻力。这也增加了碾磨过程的额定电耗。
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_ Significant increase of mill differential pressure. 磨机压差的显著增加。
_ Power consumption (kW) of the main drive unit of the mill considerably increases as a consequence of the higher rolling resistance. 主传动装置的电耗由于更高的碾磨阻力而增加。
Possible causes:可能的原因
_ Material feed is excessive. 过度的进料
_ Grinding force is insufficient. 碾磨压力不足
_ Discharge of ground material is not correct. 排出的碾磨料不好 _ Nozzle ring is blocked. 喷嘴环堵塞
_ Decrease of gas volume passing the mill. 通过磨机的气体量减少
_ Increased number of material circuits inside the mill by separator adjustment (towards finer finished product). 由于选粉机的调整，磨机内料循环的次数增加(产品更细)
3.5.5 Significant decrease of mill exit gas temperature
磨机存在的气体温度显著地降低
The causes for a decrease of the mill exit gas temperature can be as follows: 磨机存在的气体温度降低的原因如下：
_ Feed quantity for the coal mill is excessive. 煤磨喂料过多
_ Decrease of exhaust gas temperature of the heat exchanger or reduction of the hot gas quantity supplied by the heat exchanger.热风炉的热风温度降低或者热风炉提供的热风量减少。
_ Reduction of the hot gas quantity supplied to the mill due to increase of mill differential pressure (filling ratio) or of filter differential pressure.提供给磨机的热风量由于磨机压差增加(磨内填充料增加)而减少，或者收尘机的压差增高而使磨机的压差降低。 _ Considerably higher moisture content of the feed material.进料的含水量相当高 _ Heating-up of the plant was made too quickly.系统加热过快
_ Mill operation started at insufficient temperature downstream of the mill.磨机在出磨风温不足的情况下启动磨机。
If the controller “gas temperature downstream of mill” is unable to set the requested tem-perature level, the operator shall reduce the material feed quantity in order to ensure a sat-isfactory grinding and drying process.
如果控制回路控制器调节“出磨风温”不能达到设定的温度值，控制器会降低进料量以保证合适的粉磨和干燥过程。
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