The operate of a cooling water system and cooling tower in an acid plant is to reject excess course of heat to the setting. This heat comes from a quantity of different sources: weak acid cooling, gasoline condensers, acid coolers, oil coolers, refrigeration tools, and so forth.
Cooling towers use evaporation because the means of cooling the circulating water. They’re designed to expose the maximum transient water floor to the maximum circulation of air, for the most important time frame.
Design Wet-Bulb Temperature
A wet-bulb temperature that’s not exceed in no more than 5% of the total hours during a standard summer is mostly used because the design wet-bulb. A worth of 5% is chosen as a result of the hours by which the wet-bulb temperature exceeds this temperature are seldom consecutive and normally occur for less than brief durations of time.
The wet-bulb temperature that’s specified is usually an ambient wet-bulb moderately than an entering wet-bulb. The coming into wet-bulb temperature is the value used to design the tower and may or will not be the identical as the ambient wet-bulb. If the ambient wet-bulb is specified, the vendor might alter the wet-bulb temperature he makes use of for sizing the tower upwards to account for any potential recirculation.
There are mainly two types of cooling tower usually use in an acid plant:
Counter-Present Cooling Towers
In counter-current towers, air moves vertically upward by way of the fill, counter to the downward fall of water. Water is distributed throughout the fill using a system of headers, feed pipes and sprays. In acid plants these towers are typically induced draft.
In crossflow towers, air moves horizontally by means of the fill across the downward fall of water. Hot water is delivered to the recent water basin the place it is distributed by gravity across the fill by metering orifices within the floor of the basin. In acid plants the towers are usually induced draft.
The dimensions of a cooling tower is affected by 4 primary parameters:
2. Temperature Range
3. Strategy to Wet-bulb
four. Wet-bulb Temperature
Tower size is straight proportional to the heatload. If heatload is doubled, the tower size doubles.
The temperature vary is the difference between the cooling water return temperature (scorching) and cooling water provide temperature (chilly). The range should be maximized to attenuate the size of the cooling tower and the full circulating water move. Nonetheless, this is offset by will increase in the size of heat trade equipment in the plant as a result of lower LMTD’s.
The dimensions of the cooling tower varies inversely with the temperature range. Rising the vary, will increase the driving force between the recent water temperature and the wet-bulb temperature just like a normal heat exchanger.
Approach to Wet-bulb
Tower size varies inversely with the strategy to the wet-bulb temperature. At a 5oF approach, the scale of the cooling tower begins to increase asymptotically. In essence, it might take a tower of infinite dimension to cool the water to the wet-bulb temperature.
At fixed heatload, temperature range and approach to the wet-bulb temperature, the tower measurement varies inversely with the actual wet-bulb temperature. The reason for this is that many of the heat switch occurs by evaporation and the air’s ability to absorb moisture reduces with temperature.
Cooling Tower Followers
Two velocity fans ought to be specified for all cooling towers. The excessive and low speeds permits extra flexibility in the management of the cooling water temperature. In climates with extreme winters, the fans needs to be reversible permitting the towers to be de-iced.
Fans are either belt driven or shaft driven via a gear field. Belt pushed models have motors positioned contained in the tower in a high humidity surroundings. Shaft driven models typically have the motors situated outdoors the tower.
Cooling Tower Bypasses
Cooling tower bypasses are usually specified for towers installed in chilly climates. The bypass is used to stop overcooling of the water when there may be little or no heatload in the system. The bypass ought to discharge into the tower basin so far as doable from the cooling water pump suctions. This reduces the chance of cavitation due to disturbances within the stream of water to the pump suctions.
Supplies of Building
Cooling tower buildings are fabricated utilizing primarily 3 supplies: wood, concrete and steel. In acid plant cooling towers the predominant building material is wood. Steel towers are used often while concrete towers are rarely used.
In wood towers, Californian Redwood and Douglas Fir are the two most extensively used woods. All wood utilized in a cooling tower should be handled with a preservative to forestall decay. Chromated Copper Arsenate (CCA) was initially used as a preservative however because of its arsenic content it has been changed by Acid Copper Chromate (ACC).
A lot of the smaller, manufacturing unit constructed towers are constructed of galvanized steel. Some local constructing codes and/or fire codes require large towers to be constructed of steel. Stainless steel has been used now and again however its increased cost make it extraordinarily rare
The 2 commonest materials for tower fill is wood and plastic. Splash type fill might be manufactured from wooden or plastic. Film type fill is usually product of polyvinyl chloride (PVC). The benefit of PVC as a cloth is that it is of course fireplace resistant whereas other plastic must be specially handled.
Cooling Tower Standards – CTI
Within the industry, standards for cooling towers is arrange by the Cooling Tower Institute (CTI). The CTI is a self-governing, non-profit technical affiliation devoted to the improvement of know-how, design, efficiency and upkeep of cooling towers.