Steam Production and Distribution in Industrial Settings
Steam Production and Distribution
A system of steam production and distribution generally consists of the following items:
- One or more boilers that can burn coal, fuel oil, gas, etc. In industry, fuel oil is often used as fuel.
- The water used must meet certain requirements, according to the rules, requiring the installation of a treatment plant.
- Once treated, the water must pass through a degasser, which removes oxygen and combustible gases.
- Feed pumps are responsible for bringing water from the degasser to the boiler.
- At the exit of the boiler, there is a sewage system and a series of steam branches coming out of this, responsible for supplying steam to all points of consumption.
Steam Plant Variants
The steam plant can be considered two main variants:
- Produce steam only
- Produce steam and electrical energy
In the first case, as shown in the previous figure, the steam will be produced at a pressure equal to or slightly higher than that required by the process. In the distribution, there may be one or more pressure levels. In the second case, electricity is obtained, and steam expansion will be used in the process. In practice, pressures of 100-110 kg/cm2 are used in boilers, and back pressure is imposed by the process. A further description of these facilities will not be developed since it would leave the purpose of this document. As will be explained later, a good network of condensate recovery is very important. The hot condensate will go to the degasser and then to the boiler. The recovery will prevent the use of cold water supply, thus saving energy.
Condensate Recovery System
A condensate recovery system requires, first, proper trap installation and maintenance, with the idea that the capacitor can be fully evacuated from the steam. In the two previous figures, this type of installation can be seen. Traps evacuate the condensate to a condensate drain, which will lead either directly into the degasser or to an expansion tank. In the expansion tank, there is flash steam that is normally used in the degasser, and a condensed version will also go to the degasser.
Air and Hot Gas Facilities
The facilities of air and hot gases are also widely used in industry. Air is used in combustion processes in coolers and cooling towers, drying processes, etc. The hot fumes are used in the oven to heat the combustion air, thus improving combustion performance. Here, the air heater plays an important role, where sensible heat from the smoke is used (heat due to the temperature difference in the environment). The air goes to the burners by a forced draft fan, and hot fumes are taken at the foot of a chimney by an induced draft fan that passes through the preheater and then returns to the cooler chimney, where they are evacuated to the atmosphere. In a drying plant, hot gases from the combustion air are mixed to lower your temperature and get the required temperature for the process. The following figure shows an installation where there is a recycling of hot gases that go to the flask to reduce the excess air and improve performance. A second use of the sensible heat of the gas fireplace is achieved in the changer to preheat the combustion air. Technical fluids are used in chemical processes where the use of water or saturated steam as a heating fluid forces working at high pressures. To avoid all this, technical fluids with a high boiling point are used, offering great advantages: the heat exchange surfaces in the heat exchanger can be kept small, with slight differences in temperature, and the thermal transmission facility may be operated with small overpressure.
Condensate in Transport
In any steam pipe, a part of it condenses due to losses by radiation and convection. If condensate is not removed from the steam, it will accumulate by gravity in the low points of the installation until the vapor pressure moves it. Thus, when the passage of vapor plugs is driven by it at high speed until it reaches an obstacle such as a valve or a change of direction, it can cause serious damage to the installation. This is the water hammer.
Effects of Water Hammer
This phenomenon can have two effects: noise and stress on pipes and fittings. The way to drain the pipe sections is to install wells and drip traps, spaced 50 to 80 m as appropriate. The presence of the drip hole, with the same diameter and depth as the main pipe, as shown in the figure below, ensures that all condensate gets to the trap.