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热处理熔炉的调制燃烧器燃烧控制

高炉和窑

烧结厂

用于欧陆图形监控器的高炉煤气点火头应用产品

炼钢／BOS 工厂

均热炉

连续退火和镀锌作业线

单堆叠和多堆叠分批退火

烧结厂

烧结厂的功能是为高炉提供烧结物，一种混匀矿石、熔剂和焦炭的混合物（被部分“烘烤”或烧结）。在这种形式下，原材料可以在高炉中有效地混合，从而使生产出来的产品具有更好的一致性和可控性。图 1 显示了一个烧结厂的简图。

原材料从库存仓送入烧结厂。它们在每个储料仓配备的称量斗中按正确的比例混合，如果要返回精确的值，则使用冲击计替代称量斗。在整个烧结过程中，称重都是持续进行的。进行过称重的原材料沿着传送带送到搅拌筒中，在这里手动或按照原材料重量的计算比例将水加入搅拌筒中。

焦炭的含水量是在索状辊式给料斗中测量的，用于调节次生水的流速。也可以测量混合磁导率，用于修改所需的水量。

混合好的原材料通过辊式给料机从贮水槽输送到索带上。通过调节节流板可以设置并保持料床的深度，节流板安装了探针，用于检测原材料的深度，并启动调整辊式给料机速度。通过自动调整具体原材料仓的进料量，可以保持给料机中的原材料的量恒定不变。

图 1 烧结厂简图

烧结

原料混合物通过点火罩点火，点火罩混合了焦炉煤气、高炉煤气，有时还有天然气。混合物的发热值和炉罩温度的设置是可以控制的。提供独立的控制系统通过调节点火罩下面的风箱节气阀来维持固定的炉罩压力。

带式烧结机是一个热烧结物的移动式输送带，使烧结物在离开炉罩后继续“烘烤”，通过带状通风机从烧结物上收集空气。

烧结过程中一个重要部分是烧穿。在该过程中，烧结层已经完全烧穿它的剖面，通过烧结层下面的温度探测器检测。烧穿是可以实现的，但是不会在点火罩点火后立即发生。通过对压力的测量控制主风机气窗来保持输送带上的气流收集为预置值。这个值将控制烧穿发生的点。

烧结操作

在输送带尾部，烧结物穿过齿辊破碎机和热屏风，进入旋转环式冷却机中。许多风扇通常都用于冷却，冷却器的速度由以下因素决定：

输送带速度
烧结床深度

通过热屏风去除的粉末被送到返矿槽中。

冷却后，烧结物被输送到卸载仓中。在这一过程中，通过改变出口给料速度（通常是振动筛）来控制水平。

然后，烧结物被传送到冷筛部分，在这里被输送到破碎机，并进行筛分，获得某一具体粒度范围的颗粒。小于所需大小的烧结物将通过皮带秤，和热粉末一起送回至返矿槽。

冷却粉末的重量和所产生的总粉末的重量之间的差值，用于计算热粉末的重量。热返矿屑和冷却返矿屑生产率的任何异常变化都可能预示着一个工厂故障。

以下因素可能会影响产生粉末的量：

混合控制
颗粒尺寸
化学性质
重量
含水量
烧结床深度
点火罩温度和压力
热筛选

烧结物的两个重要属性一个是碱性度，由石灰石的量控制，另一个是强度，由含碳量控制。

烧结物现在适合在高炉中使用。传送带将原材料输送到高炉料仓，在这里加入其他原料形成高炉配装料。

搅拌筒湿度控制

首次加水的量与输入搅拌筒的原料混合物的重量成比例。使用图 2 所示的欧陆过程自动化控制模块可以容易地实现该操作。

图 2 搅拌筒湿度控制

二次加水的给定值通常与原料混合物皮带秤 PV 值成比例。要获得更高的精确度，可使用湿度计读数来修正原材料／含水率。这样可以根据原料混合物所测量的含水量纠正水流量。

级联控制并不经常使用，但是因为水流环路响应比湿度环路响应更快，因此可以获得更好的结果。

点火罩温度控制

图 3 描述选择了控制比的点火罩温度控制的执行过程。

图 3 点火罩温度控制

采用定比空气引导温度控制，温度要求为气流提供一个给定值。按照气流以固定比例混合燃料可以获得更有效的燃烧率。

另一方面，由于采用可变比空气引导温度控制，气流是固定的，炉罩温度控制器输出（热需要信号）将给出燃气控制器的比例给定值配平输入信号。该方法通常在比较容易获得廉价燃料（例如高炉煤气）时使用。

点火罩压力控制

通过改变点火罩下面风箱里的节气阀设置来实现该功能。单环路 PID 控制器通常用于将压力自动保持在一个给定值上。

点火罩可燃气体的发热值控制

高炉煤气和焦炉煤气用于给点火罩喷嘴提供燃料。燃料的发热值通过一个独立的控制环路控制为一个恒定的值。如果输送带停止，数字信号将迫使点火罩为“低火状态”，并保持此状态，直到输送代重新启动。

如果燃料的发热值被控制在预定义限制内，大约为 4,000 - 6,000 kJ/m3，那么是比较容易保持点火罩温度为常数的。通过将焦炉煤气和高炉煤气进行混合，可以获得该发热值。图 4 显示了发热值控制策略。

图 4 点火罩可燃气体的发热值控制

烧结终点控制

烧结终点最好是在接近输送带末尾的地方。通过改变带式机速度进行控制。许多变量会影响烧结终点，例如带式机原料床深度、含水率和烧结物的质量。

带式机速度可以通过手动控制，或是通过测量作为烧结终点指示的废气温度来进行控制。如果烧结终点发生过早，那么平均废气温度将上升。如果发生的过迟，那么废气温度将降低，且带式机速度放慢以进行补偿。

图 5 烧结终点控制

风箱温度可用于改善监控效果，并增加给定值偏离值。图 5 显示了它的控制策略。

主风机吸力和废气超温控制

主风机产生的吸力是通过风机入口旁的气窗改变的，而气窗是由风机吸力控制器控制的。如果废气温度增加超过了安全工作限制，那么选择器开关将使废气过热温度控制器对气窗进行定位。

冷却器速度控制

在离开带式输送机后，热烧结物在回转式冷却器上冷却。

回转式冷却器的速度是受控的，以匹配根据带式机原料床深度和速度确定的带式机要求。

^{Figure 1: Simplified diagram of a sinter plant}

Sintering

The raw mix is ignited by the ignition hood, which is fuelled by a mixture of coke oven gas, blast furnace gas and sometimes natural gas. The calorific value of the mixture and the set hood temperature are controlled. A separate control system is provided to maintain a fixed hood pressure by adjusting the windbox dampers immediately under the ignition hood.

The sinter strand is a moving conveyor of hot sinter, which continues to ‘cook’ after leaving the hood, where air is pulled from the sinter by a strand draught fan.

An important part of the sintering process is burn-through. This is where the sinter layer has completely burned through its section and is detected by temperature probes under the sinter bed. Burn through should be achieved but must not occur too soon after the ignition hood. The draught on the strand is maintained at a preset value by controlling the main fan louvers from pressure measurements in the wind main. This governs the point at which burn through occurs.

Mixing drum moisture control

The amount of primary water added is proportional to the weight of raw mix entering the mixing drum. This can be easily achieved using a Eurotherm Process Automation control module as shown in Figure 2.

^{Figure 2: Mixing drum moisture control}

The secondary water feed setpoint is frequently taken as a proportion of the raw mix belt weigher PV. For greater accuracy, the moisture meter reading is used to trim the material/water ratio. This corrects the water flow rate according to the measured moisture content of the raw mix.

Cascade control is not always used but since the water flow loop responds faster than the moisture loop it does produce better results.

Sinter handling

After the end of the strand, the sinter passes through a spiked roll crusher and the hot screens to the rotating circular cooler. A number of fans are usually used for cooling, and the speed of the cooler is determined by:

Strand speed
Bed depth

The fines removed by the hot screens are conveyed to the return fines bin.

After cooling, the sinter is passed into the discharge bunker. At this stage, the level is controlled by varying the outlet feed rate (usually vibros).

The sinter then passes to the cold screening area, where it is passed through crushers and screens to produce particles in a specific size range. Sinter below the required size passes over a belt weigher and returns with the hot fines to the return fines bin.

The difference between the weight of the cold fines, and the weight of the total fines produced, gives a measure of the hot fines. Any abnormal variation in the rate of production of hot or cold return fines indicates a possible plant fault.

The following factors can affect the rate at which fines are produced:

Mix control
Particle size
Chemistry
Weight
Moisture content
Bed depth
Ignition hood temperature and pressure
Warm screens

Two important properties of sinter are basicity, which is controlled by the amount of limestone, and strength, which is controlled by coke content.

The sinter is now suitable for use in the blast furnace. Conveyors transport the material to the blast furnace stock house, where it is added to other materials to form the blast furnace burden.

Ignition hood temperature control

Figure 3 depicts the implementation of ignition hood temperature control with options for the control ratio.

With the fixed ratio air lead temperature control, the temperature demand provides a setpoint for the air flow. The fuel follows the air flow in a fixed ratio making this a fuel efficient method.

On the other hand, with variable ratio air lead temperature control, the air flow is fixed and the hood temperature controller output (the heat demand signal) feeds the ratio setpoint trim input of the gas controller. This method is normally used when there is a readily available source of cheap fuel e.g. blast furnace gas.

Ignition hood pressure control

This is normally achieved by varying the setting of dampers in the windboxes under the ignition hood. A single loop PID controller is generally used to automatically maintain the pressure at a desired value.

^{Figure 3: Ignition hood temperature control}

Calorific value control of ignition hood fuel gas

Blast furnace gas and coke oven gas are used to fuel the ignition hood burners. The calorific value of the fuel is controlled to a consistent value by a separate control loop. If the strand stops, a digital signal forces the ignition hood into a ‘low fire state’ and holds it there until the strand re-starts.

It is easier to keep the ignition hood temperature constant if the calorific value of the fuel is controlled to within pre-defined limits, about 4,000 - 6,000 kJ/m3. By mixing coke oven gas with blast furnace gas, this calorific value is achieved. Figure 4 shows the calorific value control strategy.

Calorific value of ignition hood fuel gas

^{Figure 4: Calorofoc value control of ignition hood fuel gas}

Burn-through point control

Burn-through point should ideally occur near the end of the strand bed. It is controlled by altering the strand speed. A number of variables will affect the burn-through point, such as strand bed depth, water content and the quality of the sinter.

The strand speed is either controlled manually, or by measuring the waste gas temperatures as an indication of the burn-through point. If it occurs too early, the average waste gas temperature rises. If it occurs too late, the waste gas temperature decreases and the strand speed is slowed to compensate.

Windbox temperatures can be used to improve the monitoring and are added as a setpoint bias. Figure 5 shows this in the control strategy.

^{Figure 5: Burn-through point control}

Main fan suction and waste gas overtemperature control

The suction produced by the main fan is varied by louvers near the fan inlet, which are controlled by a fan suction controller. If the waste gas temperature increases above a safe working limit a selector switch allows the waste gas overtemperature controller to position the louvers.

Cooler speed control

After leaving the strand, the hot sinter is cooled on a rotary cooler.

The speed of the rotary cooler is controlled to match the strand demand defined by the bed depth and the strand speed.