Selection of Steam Traps in Chemical Engineering Design

Steam trap and its selection method

   Trap is a device that automatically eliminates non-condensable gases such as steam condensate and air in heating equipmen t or steam piping, and does not leak steam. As the trap has the role of steam drainage, steam heating equipmen t can be evenly to heat, make full use of steam latent heat pipe to prevent the occurrence of water hammer. It is to ensure a variety of heating process equipmen t required for the temperature and heat and can work properly as an energy-saving products.

1.1 The classification of traps

   Many different types of traps, each with different performance. Steam trap to be able to "identify" steam and condensate, in order to play the role of steam drainage. "Identification" of steam and condensate is based on three principles: density difference, temperature difference and phase transition. Three types of traps are manufactured according to three principles: mechanical, thermostatic, thermodynamic.

1) mechanical trap, also known as float type trap, is the use of condensate and steam density difference, through the condensation water level changes, so that float (ball or bucket) driven valve flap open or closed, to block steam Drainage purposes. Mechanical type steam traps have a low degree of undercooling and are not affected by working pressure and temperature changes. Water is discharged without heating in the equipmen t, so that the heating equipmen t can achieve the best heat transfer efficiency. Mechanical trap with free float, lever float, floating bucket, inverted bucket, etc .;

2) Thermostatic type steam trap is the use of steam and condensate water temperature difference caused by a variant or expansion valve driven valve opening and closing valves. Thermostatic traps have a large undercooling degree, generally undercooling 15 degrees to 40 degrees, it can use part of the condensation of sensible heat, there is always a high temperature before the valve condensate, no steam leakage, energy-saving effect is significant . Thermostatic traps have bellows, steam pressure or balance pressure type, bimetallic, liquid expansion;

3) Thermodynamic traps are based on the principle of phase change, by steam and condensate flow through the flow rate and volume changes in different thermodynamic principles, the valve up and down to produce different pressure, drive valve switch valve. Because of the thermal power type steam trap work power comes from the steam, therefore the steam wastes is bigger. Thermodynamic traps are divided into disc type, pulse type, labyrinth type or micro hole type.

1.2 trap selection instructions

   In the heating process of conveying, soda separation, heating, drying, heat preservation, heating, disinfection, distillation, concentration, cooking, heat exchange, heating and air conditioning, in order to ensure the required heat quantity, Condensate to prevent steam leakage, you must install the trap. For the selection of steam trap, requiring high sensitivity, accurate resistance to steam drainage, no leakage of steam, can improve the utilization of steam, reliable performance, high back pressure, long service life, easy maintenance and other conditions.

   Steam trap selection principles:

1) If the equipmen t is required to have the fastest heating rate, the heating temperature is strictly controlled, and keep in the heating device can not accumulate condensate, you should choose to be saturated water mechanical trap; 2) If the heating equipmen t has a greater heat, according to the use of the displacement of the number of equipmen t, the choice of trap must consider the safety factor; 3) the use of equipmen t to reduce the amount of water, Trap is to determine the displacement of the pressure difference.

Specific selection is as follows:

1) mechanical type steam trap maximum back pressure of 80%, the work of high quality, is the production process heating equipmen t, the best trap. Small gate valve sensitivity of the larger gate. In addition to the inverted bucket trap can rule out a small amount of hot and cold air, this type of valve can not rule out the air. Free floating ball structure is simple, high sensitivity, row of saturated water, anti-water hammer, poor dirt resistance, suitable for large-caliber and large displacement, but the manufacturing process is complex.

2) Thermostatic type steam traps can be installed in the upper part of the steam equipmen t, simply use the exhaust valve. The liquid expansion type is suitable for the heat tracing pipeline with low heating temperature and the pipeline for heating. Steam pressure type or balanced pressure type Structure is simple, action sensitive, continuous drainage, exhaust air, good performance, small leakage, but poor water and dirt resistance, wide range of applications can be used as steam system exhaust valve . Bellows-type heating system is widely used for hydrophobic, but also as a steam system, air valve. Bimetallic action sensitivity is not high, continuous drainage, good drainage, undercooling and adjustable, from low to high pressure are applicable, the maximum temperature of up to 550 degree celsius . Anti-fouling, anti-water hit strong.

3) Thermodynamic power traps have a high sensitivity to handle condensate, small opening and closing, low inertia and fast switching speed. Disc-type traps for high temperature and high pressure steam pipes, dryers, heaters and super heated steam equipmen t. Pulse steam trap back pressure is low, suitable for rotating drum drying siphon drainage, to exclude a certain amount of hot and cold air. Labyrinth or porous trap simple structure, continuous drainage, exhaust air. Micro-type for small displacement, labyrinth for large displacement.

1.3 Trap installation requirements

    Thermodynamic trap should be installed in the horizontal pipe; float type trap must be installed horizontally, arranged in the outdoor should take the necessary anti-freezing measures; bimetallic trap can be installed horizontally or upright; pulse traps generally installed In the horizontal pipe, the valve cover upward; inverted bucket trap should be installed horizontally not tilt; install the trap, the flow direction arrow on its body must be consistent with the flow of condensate in the pipeline, or the trap to lose its function.