Steam - The Energy Fluid

Steam provides a means of transporting controllable amounts of energy from a central, automated boiler house, where it can be efficiently and economically generated, to the point of use. Therefore as steam moves around a plant it can equally be considered to be the transport and provision of energy.

For many reasons, steam is one of the most widely used commodities for conveying heat energy. Its use is popular throughout industry for a broad range of tasks from mechanical power production to space heating and process applications.

蒸汽 – 载能流体

蒸汽提供了一种手段，将总量可控的能量从中央自动化锅炉房传送到使用点，而在锅炉房能量可以有效且经济地产生。因此，当蒸汽在工厂各处流动时，同样可被视为能量传输和供应。

基于多种理由，蒸汽是用于传递热能的最广泛使用的货品之一。蒸汽传能在工业中普遍使用于从产生机械功到空间加热和工艺应用等广泛的使命。

Other methods of distributing energy

The alternatives to steam include water and thermal fluids such as high temperature oil. Each method has its advantages and disadvantages, and will be best suited to certain applications or temperature bands.

Compared to steam, water has a lower potential to carry heat, consequently large amounts of water must be pumped around the system to satisfy process or space heating requirements. However, water is popular for general space heating applications and for low temperature processes (up to 120°C) where some temperature variation can be tolerated.

Thermal fluids, such as mineral oils, may be used where high temperatures (up to 400°C) are required, but where steam cannot be used. An example would include the heating of certain chemicals in batch processes. However thermal fluids are expensive, and need replacing every few years - they are not suited to large systems. They are also very ‘searching’ and high quality connections and joints are essential to avoid leakage.

能量分送的其它方法

蒸汽的替代物包括水和热流体，例如高温油。每种方法都有其优点和缺点，各自在特定应用或温度范围内都适得其所。

与蒸汽相比，水热效较低，必须在系统周围泵送大量的水以满足工艺或空间加热要求。然而，水普遍用作一般空间加热和低高温工艺(上限120℃)，且对温度起伏变化较可接受。

需要高高温时(上达400℃)，而又不能使用蒸汽的情况下，可以使用热流体，例如矿物油。 常见实例如批量生产工艺中加热某些化学品等。然而，热流体比较昂贵，并且需要每几年更换一次 – 同时也不适合大型系统。油料“见缝即钻”和必须采用高质量的连接件和接头，以避免泄漏。

The final choice of heating medium depends on achieving a balance between technical, practical and financial factors, which will be different for each user.

Broadly speaking, for commercial heating and ventilation, and industrial systems, steam remains the most practical and economic choice.

加热介质的最终选择取决于技术，操作和成本因素之间达成的平衡，这对每个用户都各不相同。

总体来说，对于商业供暖和通风以及各种工业系统，蒸汽仍然是最实际和最经济的选择。

At this point it has reached boiling point or its saturation temperature, as it is saturated with heat energy.

If the pressure remains constant, adding more heat does not cause the temperature to rise any further but causes the water to form saturated steam. The temperature of the boiling water and saturated steam within the same system is the same, but the heat energy per unit mass is much greater in the steam.

At atmospheric pressure the saturation temperature is 100°C. However, if the pressure is increased, this will allow the addition of more heat and an increase in temperature without a change of phase.

Therefore, increasing the pressure effectively increases both the enthalpy of water, and the saturation temperature. The relationship between the saturation temperature and the pressure is known as the steam saturation curve.
水，加热到某一点，已经达到沸点或其饱和温度，即已被热能所饱和。

如果压力保持恒定，输入更多热量不会导致温度进一步升高，但会使水形成饱和蒸汽。同一系统内沸水和饱和蒸汽的温度相同，但是蒸汽中每单位质量的热能大得多。

在大气压下，饱和温度为100℃。然而，如果压力增加，就能容许更多热量输入和温度上升而不改变相位。

因此，增加压力有效地增加了水的焓和饱和温度。

Water and steam can coexist at any pressure on this curve, both being at the saturation temperature. Steam at a condition above the saturation curve is known as superheated steam:

• Temperature above saturation temperature is called the degree of superheat of the steam.

• Water at a condition below the curve is called sub-saturated water.

水和蒸汽可以在饱和曲线上的任何压力下共存，两者都处于饱和温度。在高于饱和曲线的条件下的蒸汽被称为过热蒸汽：

•温度高于饱和温度称为蒸汽过热度。

•低于曲线条件下的水称为亚饱和水。

 

If the steam is able to flow from the boiler at the same rate that it is produced, the addition of further heat simply increases the rate of production. If the steam is restrained from leaving the boiler, and the heat input rate is maintained, the energy flowing into the boiler will be greater than the energy flowing out. This excess energy raises the pressure, in turn allowing the saturation temperature to rise, as the temperature of saturated steam correlates to its pressure.

At 100°C, the theoretical internal energy of the saturated liquid is 418.9 kJ/kg while the theoretical internal energy of the saturated vapor is 2506.5 kJ/kg.1  Thus, there is roughly six times more energy in a saturated vapor (steam) than there is in the saturated liquid!

如果蒸汽能够以其生成速率等量地从锅炉输出，则输入额外热量仅能提高其生成速率。如果蒸汽被限闭在锅炉中，而又保持热量输入速率，则输入锅炉的能量将大于流出的能量。该过剩能量可升高压力，从而引起饱和温度升高，因为饱和蒸汽的温度与其压力是相关的。

在100℃下，饱和液体的理论内能为418.9kJ / kg，而饱和蒸汽的理论内能为2506.5kJ / kg。因此，饱和蒸气(蒸汽)中的能量比饱和液体中的约高六倍！

 

Superheated Steam

If the saturated steam produced in a boiler is exposed to a surface with a higher temperature, its temperature will increase above the evaporating temperature.

The steam is then described as superheated by the number of temperature degrees through which it has been heated above saturation temperature.

Superheat cannot be imparted to the steam whilst it is still in the presence of water, as any additional heat simply evaporates more water. The saturated steam must be passed through an additional heat exchanger. This may be a second heat exchange stage in the boiler, or a separate superheater unit. The primary heating medium may be either the hot flue gas from the boiler, or may be separately fired.

如果锅炉中产生的饱和蒸汽接触具有较高温度的表面，其温度将升高到高于蒸发温度。

此种蒸汽即为过热的，其过热度按其温度超过饱和温度的度数来描述。

蒸汽中尚存有水的时候不会发生过热，因为任何额外热量只会蒸发更多的水。饱和蒸汽必须通过单独的热交换器而形成。这可以是锅炉中第二热交换级，或单独的过热器单元。主加热介质可以是来自锅炉的热烟道气，或者可以是单独的燃烧。

Superheated steam has its applications in, for example, turbines where the steam is directed by nozzles onto a rotor. This causes the rotor to turn. The energy to make this happen can only have come from the steam, so logically the steam has less energy after it has gone through the turbine rotor. If the steam was at saturation temperature, this loss of energy would cause some of the steam to condense.

superheated steam is not as effective as saturated steam for heat transfer applications. This may seem strange, considering that the rate of heat transfer across a heating surface is directly proportional to the temperature difference across it.

过热蒸汽自有其应用，例如在涡轮机中，蒸汽通过喷嘴被喷射到转子上。这使转子转动。这个过程发生的能量只能来自蒸汽，因此在蒸汽通过涡轮机转子后，能量减少。如果蒸汽处于饱和温度，则这种能量损失将使得一些蒸汽冷凝。

过热蒸汽用于传热不如饱和蒸汽那么有效。这可能看起来难以理解，但想一下通过热表面的 热传导率与该表面的温度差是成正比的。

 

Why is steam so dangerous?

Because in order to turn water into steam (liquid to gas) it must be heated intensely past the point of boiling, therefore the resulting steam is obviously extremely hot. 

If you are referring to the danger of a catastrophic pressure vessel failure (boiler explosion) the danger comes from a three-pronged issue. Water under pressure will not boil at 212 degrees (100 C). As the pressure goes up, so does the temperature need to get the water to boil.

When a pressure vessel fails, there is the potential for an instantaneous drop in pressure from X pounds per square inches to ZERO psi. But the temperature of the water is (for example 350 degrees F) then without the pressure it will flash boil into steam. This is the theory of why locomotive boiler explosions were so deadly. It was common theory that when the firebox's roof sheet failed and the steam in the boiler evacuated into the firebox, the water flash boiler, instantly raising the pressure to 50 to 100,000psi.

蒸汽为何如此危险？

因为为了将水变成蒸汽(液体到气体)，必须急剧加热超过沸点，因此所得到的蒸汽显然极热。

如果你想到一次压力容器灾难性故障(锅炉爆炸)的危险，其危险来自三方面。压力上升，水就不会仍在100℃沸腾。压力升高，温度也要升高才能使水沸腾。

当压力容器破裂时，其潜在危险即是压力从 X psi (磅/平方英寸) 瞬时下降到 0 psi。但是水温很高（例如180℃），突然失压，就会闪蒸成蒸汽。这就是为什么机车锅炉爆炸如此致命。通常理论认为，当燃烧室的顶板失效并且锅炉中的蒸汽排入燃烧室时，水在锅炉中闪蒸，可将压力提高到50至100,000psi。

 

CORROSIVE STEAM

When the water used to generate steam contains dissolved air, oxygen or carbon dioxide, then these gases end up as contaminants in the steam. At high temperatures of steam both oxygen and carbon dioxide are extremely corrosive.

Carbon dioxide is acidic and therefore attacks metals whereas the oxygen corrodes metals and oxidises rubbers. Corrosion of metals in the presence of both oxygen and acids is forty times faster than with either alone. Boiler water is therefore normally treated not only to remove the“hardness” which would cause “furring” of the boiler but also to remove dissolved oxygen and carbon dioxide and to ensure that the steam is not only not acidic but even slightly alkaline. Boiler water treatment is a specialized subject to be covered in lengthy technical sheets but correct steam generation is important.

当用于产生蒸汽的水中含有溶解的空气，氧气或二氧化碳时，这些气体最终成为蒸汽中的污染物。在高温蒸汽下，氧和二氧化碳都具有极强的腐蚀性。

二氧化碳是酸性的，因此腐蚀金属；而氧也能腐蚀金属还能氧化橡胶。在氧和酸共同作用下，金属的腐蚀率比单一因素时快40倍。因此，通常对锅炉水要进行处理，以除去会导致锅炉“结垢”的“硬度”，而且还要去除溶解的氧和二氧化碳，并且确保蒸汽不仅不是酸性的，而且甚至是微碱性的。锅炉水处理是一个专门课题，要用冗长的技术清单加以论述，但正确的蒸汽生产很重要。


DETERIORATION OF STEAM HOSE蒸汽软管的退化

Like all rubber products steam hoses have a finite life and are subject to gradual deterioration with use.

Rubber steam hoses are oxidized and attacked by high temperature oxygen and acidic CO₂ within Corrosive Steam.

Water or moisture residing on surface and texture of inner wall of rubber steam hoses will be heated up by steam passing by and expands into vapour bubbles and break, which will crack the surface of inner wall of rubber steam hoses.

Steam hoses are mostly used at chemical and petrochemical plants. These factories and plants have aggressive atmospheres with substances such as chlorine and salt. Also, industrial hoses for steam are being dragged and used by workers in a dynamic, rough way.

These effects may result in a “popcorning” finish of rubber steam hoses sooner or later.

像所有的橡胶制品一样，蒸汽软管也有一定的使用寿命，其随着长期使用而逐渐退化。

橡胶蒸汽软管受到腐蚀性蒸汽中高温氧气和酸性CO₂的氧化和侵蚀。

存在于橡胶蒸汽软管内表面的水分或湿气会被通过的蒸汽加热，自身膨胀成蒸气泡，破裂，从而使橡胶蒸汽软管内壁的表面开裂。

蒸汽软管主要用于化工和石油化工厂。这些工厂和装置存在腐蚀性气氛，比如含氯和盐等物质。此外，用于蒸汽的工业软管被拖拉且使用者常以随动、粗糙的方式使用。

这些效应可能导致橡胶蒸汽软管的内表“爆裂”现象迟早都会发生。

未受侵蚀的蒸汽橡胶软管