直流锅炉的湿干态运行-中英文

直流锅炉的湿干态运行

Wet/Dry Operation of Once-through Boiler

一．超临界直流锅炉启动特点

ⅠStart-up characteristics of super-critical pressure once-through boiler

超临界锅炉的启动系统是超临界机组的一个重要组成部分。

Start-up system of super-critical pressure boiler is an important part of super-critical pressure unit.

由于超临界锅炉没有固定的汽水分离点，在锅炉启动过程中和低负荷运行时，给水量会小于炉膛保护及维持流动稳定所需的最小流量，因此必须在炉膛内维持一定的工质流量以保护水冷壁不致过热超温。

There is no fixed W/S separation point in super-critical pressure boiler, feedwater flow will be less than the minimum flow of furnace protection and to stabilize circulation during boiler start-up and running with low load, so it’s necessary to maintain certain working media to ensure that water wall will not get over-temperature.

设置启动系统的主要目的就是在锅炉启动、低负荷运行及停炉过程中，通过启动系统建立并维持炉膛内的最小流量，以保持水冷壁水动力稳定和传热不发生恶化，特别是防止发生亚临界压力下的偏离核态沸腾和超临界压力下的类膜态沸腾现象，保护炉膛水冷壁，同时满足机组启动及低负荷运行的要求。

The main purpose of setting start-up system is that during boiler start-up/shutdown and running with low load, maintain minimum flow in furnace by start-up system to ensure stable water dynamic force of water wall and sound heat transfer, in particular, to avoid departure from nuclear boiling(DNB) under subcritical pressure, and film boiling under super-critical pressure, so as to protect water wall and satisfy the requirements for unit start-up and operation with low load.

超临界锅炉与亚临界自然循环锅炉的结构和工作原理不同，启动方法也有较大的差异，超临界锅炉与自然循环锅炉相比，有以下的启动特点：The structure and working principle of super-critical pressure boiler are different from that of natural circulation boiler, so is the start-up method. In comparison with natural circulation boiler, super-critical pressure boiler is characterized by the following:

1．设置专门的启动旁路系统

Setting special start-up bypass system

直流锅炉的启动特点是在锅炉点火前就必须不间断的向锅炉进水，建立足够的启动流量，以保证给水连续不断的强制流经受热面，使其得到冷却。

The characteristic of start-up of once-through boiler is that before boiler light-up, it must continuously fill boiler with water to make start-up flow sufficient so as to ensure feedwater flows heating surface forcefully and continuously to cool it.

一般高参数大容量的直流锅炉都采用单元制系统，在单元制系统启动中，

汽轮机要求暖机、冲转的蒸汽在相应的进汽压力下具有50℃以上的过热度，其目的是防止低温蒸汽送入汽轮机后凝结，造成汽轮机的水冲击，因此直流炉需要设置专门的启动旁路系统来排除这些不合格的工质。

Unit system is adopted by once-through boiler of high parameter and large volume. During start-up of unit system, superheat degree of steam to warm and roll for turbine should be over 50℃ under its corresponding admission pressure, so as to avoid water impact on turbine which may be caused by low temperature steam entering turbine and condensing. Therefore, it’s required to set special start-up bypass system to discharge these unqualified working media for once-through boiler.

2．配置汽水分离器和疏水回收系统

W/S separator and drain recovery system

超临界机组运行在正常范围内，锅炉给水靠给水泵压头直接流过省煤器、水冷壁和过热器，直流运行状态的负荷从锅炉满负荷到直流最小负荷，直流最小负荷一般为25%~45%。

When super-critical pressure unit runs within normal range, through pressure head, boiler feedwater flows directly by economizer, water wall and superheater, load under once-through operation is from full load of boiler to the minimum load of direct flow which is generally 25%~45%.

低于该直流最小负荷，给水流量要保持恒定。

When it’s below the minimum load of direct flow, keep feedwater flow stable.

例如在20%负荷时，最小流量为30%意味着在水冷壁出口有20%的饱和蒸汽和10%的饱和水，这种汽水混合物必须在水冷壁出口处分离，干饱和蒸汽被送入过热器，因而在低负荷时超临界锅炉需要汽水分离器和疏水回收系统，疏水回收系统是超临界锅炉在低负荷工作时必需的另一个系统，它的作用是使锅炉安全可靠的启动及其热损失最小。

For example, in 20% load, the minimum flow is 30%, which means there is saturated steam (20%) and saturated water (10%) in outlet of water wall, the W/S mixture must be separated in outlet of water wall, dry saturated steam is put into superheater, so W/S separator and drain recovery system are needed in super-critical pressure boiler; drain recovery system is another necessary system when super-critical pressure boiler is running with load low, whose main function is to make boiler start-up safe and stable and heat loss minimize.

3．启动前锅炉要建立启动压力和启动流量

Making start-up pressure and flow ready before starting boiler

启动压力是指直流锅炉在启动过程中水冷壁中工质具有的压力。

Start-up pressure is the pressure that working media in water wall possess during start-up of once-through boiler.

启动压力升高，汽水体积质量差减小，锅炉水动力特性稳定，工质膨胀小，并且易于控制膨胀过程，但启动压力越高对屏式过热器和再热过热器的保护越不利。