How to prevent electric condensate pump failure

This guest article was posted by the Engineering team at -Inveno工程。

世界不断经历reliabili蒸汽ty issues with electric condensate pumps that can be easily resolved with a proper understanding of the condensate system and by choosing the correct electric condensate pump system. The first step is to recognize that the world’s steam/condensate systems can be divided into two major categories: nonmodulating and modulating. The majority of the condensate pumps used in steam/condensate systems are for modulating steam systems. Selecting the wrong condensate pump system can lead to significant problems: unreliable electric condensate pumps can cause major issues with safety, reliability, production, optimization, energy, and loss of condensate (water).

图1：电冷凝水泵故障

技术论文将讨论调制蒸汽系统和选择电冷凝水泵的正确方法。电冷凝水泵系统是泵送冷凝物的最节能，最可靠的方法。了解以下几点将提供选择正确的电动泵所需的信息。

Determine the type of condensate system

调节蒸汽系统将具有冷凝水/闪光蒸汽（两相流）正在从蒸汽/冷凝物工艺中排出。调节蒸汽系统意味着该过程应用程序具有蒸汽控制阀，调节蒸汽到该过程，并且控制阀可以从0％（闭合）到100％（完全开放）和两者之间的任何地方运行。（见图1.）图1表示壳和管热交换器，但示例可以是带有蒸汽阀的任何蒸汽过程，该过程可以调节以接近或0 psig。

Examples of modulating steam processes;

• 任何产品温度出口温度为220^of或更低

0 psig的蒸汽温度为212^oF，因此需要非常低的蒸汽压力。很多过程温度在180^oF，例如CIP系统和处理热水系统。

蒸汽控制阀和过程热交换器之前的蒸汽压力可以根据过程条件而变化（P2读数）。P2处的压力范围从向蒸汽控制阀（P1）一直到“ 0”压力范围。

在这种情况下，冷凝水不能以以下方式排放；

1. 排放装置后的管道没有抬高（蒸汽陷阱或冷凝水阀）
2. The condensate line cannot be pressurized

取而代之的是，从蒸汽过程的冷凝水流必须以0 psig（P5）的压力排放到冷凝物线中，并将其输送到处于处于或接近“ 0”压力的通风冷凝接收机罐中。

Figure 2 depicts the typical condensate receiver tank arrangement, where the flash steam is allowed to be vented to the atmosphere.

图2：蒸汽控制阀

为什么需要泵送冷凝水？

使用电冷凝水泵有几个原因，但仅在需要冷凝水泵的情况下安装冷凝水泵。不需要安装的一定比例的冷凝水泵，可以从冷凝水系统中消除。以下有关系统中需要冷凝水泵的示例。

1. 排水装置后的冷凝水返回管道高程（蒸汽陷阱或控制阀）
2. 冷凝水返回线压力高于排水装置入口处的蒸汽压力（蒸汽陷阱或控制阀）
3. Condensate return line piping length or long distance back to the steam generation location

Simple Point,但是，经常被遗忘的“ P1或蒸汽陷阱入口必须始终高于蒸汽陷阱的出口P2”。如果P2高于P1，则不会从该过程中删除冷凝物。

Determining the condensate temperature that needs to be pumped

冷凝水以两相流（冷凝水/液体和闪光蒸汽/蒸气）的形式返回冷凝物系统。除非植物不隔离冷凝物线或冷凝水成分，否则闪光蒸汽将被冷凝至冷凝水，结果将是由于未绝缘的冷凝水系统而导致的，含量损失。

图3：标准电冷凝水泵

However, the condensate system is usually insulated and there will be two phase flow back to the condensate tank. Therefore, the condensate temperature will be close to 212^oF这必须是您选择过程的一部分。

凝结温度高于180^oF;电动泵需要NPSH

Figure 4: Low Condensate Temperature Electric Pump Unit

在选择冷凝水泵时应研究的关键因素是NPSH。Due to the two-phase flow (flash steam and condensate) which will keep the condensate temperatures close to 212^oF will require NPSH to ensure no泵空气。

图3：是一个具有180的低温冷凝物单元^oF condensate temperature design; which is due to theNPSH不足泵送180以上的凝结物^oF.冷凝物是重力冷凝物系统，将接近或接近212^oF;因此，在操作过程中，冷凝水泵将在不可靠的操作过程中进行起泡。

NPSHis determined by factors such as temperature, altitude, static head, and capacity. Condensate pumps are available that have been specifically designed to handle low NPSH, preventing cavitation, and thus able to operate at higher temperatures.

图5：NPSH

Cavitation

当液体在离心泵中进入叶轮的眼睛时，其压力会降低。如果叶轮眼中的绝对压力下降到流体的蒸气压，则蒸气口袋开始形成。当这些蒸气口袋沿着叶轮的叶片中流动，压力增加，口袋塌陷。

图6：泵空气

蒸汽气泡的这种崩溃称为空气气泡。

Cavitation is not only noisy but also damages the pump impeller, shaft and seal, and, over time, may reduce pumping capacity. NPSH refers to the minimum suction pressure, expressed in feet of water column, that is required to prevent the forming and collapsing of these vapor pockets.

The diagram shows the change in system pressure (Ps) as the fluid travels through the impeller. To prevent cavitation, Ps must remain above the vapor pressure. The top curve shows system pressure (Ps) remaining above fluid vapor pressure as it passes through the pumps; cavitation cannot occur. The bottom curve shows Ps falling below the vapor pressure as it enters the impeller eye. This will cause cavitation. The cutaway view of a pump on the picture shows the passage of flow through the impeller.

NPSHis determined by factors:

• 温度
• 高度
• 静态头
• Capacity

NPSH =气压压力，英尺。+吸力上的静态头。- 吸入管道中的摩擦损失，英尺 - 液体的蒸气压力，ft。

定义为吸气压力减去蒸气压在泵抽吸处的液体英尺中表达的。从泵抽吸上方的水高度产生的结果。

吸气头=进入泵吸力的液体的总压力

NPSH的两个值

NPSH有两个值：NPSHR和NPSHA。

NPSHR（必需）是防止泵空气泵的吸气头的量，由泵设计确定，并在泵曲线。它在不同的泵的不同泵之间有所不同，在相同设计的不同泵之间，随着任何一个泵的容量和速度而变化。这是泵的制造商必须提供的值。

NPSHA (available) is the amount of suction head available or total useful energy above the vapor pressure at the pump suction. This is determined by the system conditions. NPSH typically is measured in ft of liquid.

选择冷凝水泵系统

以下是在冷凝水泵选择过程中的项目检查清单

• 需要冷凝物容量；
  1. 最大
  2. Minimum
  3. 普通的

The plant needs to document the required capacity of the condensate pumping system. Condensate pumps are used in a variety of process and heating applications. The maximum load is never usually achieved and there is typically a great variance between the normal high condensate flow and the minimum condensate flow. Therefore, careful consideration must be given when defining the condensate capacity.

• Condensate temperature
• 指定温度所需的NPSH
• 泵速
  1. 永远不会超过1800 rpm
• 泵所需的排放压力
• Single or dual pump
  1. Single pump is preferred
  2. 始终设计可靠性，而不是失败
• 坦克尺寸
• 闪光蒸汽，忽略蒸汽系统
  1. 蒸汽的排气需要在低速下完成
  2. 建议低于3,000 fpm
  3. 向冷凝水供应商提供所需的蒸汽量
• 控制冷凝水的流动
  1. 开关
     1. 流速为12,000磅。每小时或更少
  2. 连续流
     1. 流速为12,000磅。每小时或更高

• 坦克材料
• 油箱的腐蚀津贴
• 位置和安装

PISG versus Feet of Head

Each pound of pressure developed by a pumping system is equal to 2.31 feet of head. Therefore, 10 pounds of pressure (PSIG) will lift water vertically 23.1 feet.

This can be calculated for any setting using the following formula:

每平方英寸磅=头为脚 / 2.31

Head in Feet = Pounds per sq. in. x 2.31

Sizing of Receivers

冷凝水接收器或储罐的尺寸应足以使冷凝水存储至少10分钟。

Example:

4,000磅。每小时（凝结能力）

• 4,000 divided by 8.3 (lbs. per gallon) divide by 60 (minutes in an hour) = 8.03 gpm
• 03 gpm x 10 = 80.3 - gallon storage tank