Blowdown Rate of Closed Cooling Towers: Causes, Impact and Control

Blowdown rate is a key parameter of a closed cooling tower, with a direct bearing on equipment performance and operating stability. This article takes an in-depth look at why blowdown occurs, how it affects tower operation, and how it can be kept under control.

I. What Causes Blowdown

In a closed cooling tower, blowdown is mainly driven by the following two factors:

       1. Scale formation: as the cooling water circulates and its temperature drops, dissolved minerals precipitate out and settle as scale on the fill or condenser surfaces. As scale builds up, it steadily reduces heat transfer efficiency, so the equipment has to be cleaned and blown down at regular intervals.

       2. Suspended solids: cooling water can carry suspended matter such as silt and dust, which gradually settles at the bottom of the tower during circulation and has to be drained off periodically.

II. How Blowdown Rate Affects the Cooling Tower

Both too much blowdown and too little are bad for the operation of a closed cooling tower:

       1. Excessive blowdown: heat transfer efficiency falls and operating costs rise, while large volumes of blowdown also mean higher water consumption and a heavier wastewater treatment load.

       2. Insufficient blowdown: scale and suspended solids accumulate inside the equipment, impairing heat transfer and, in severe cases, causing blockages.

III. How to Control Blowdown Rate

Keeping a closed cooling tower running steadily calls for proper control of the blowdown rate:

       1. Periodic cleaning: clean the equipment on a schedule set by water quality and operating conditions, so as to limit scale formation.

       2. Filtration: filter the cooling water before it enters the equipment to remove suspended solids and other impurities.

       3. Chemical dosing: add scale inhibitors, dispersants and similar chemicals to the cooling water as required, to control the formation and deposition of scale.

       4. Monitoring and adjustment: install water quality instruments and flow meters to track blowdown rate and cooling water quality in real time, and adjust operating parameters promptly in response to the readings.

       5. Sound design: take water quality and operating conditions fully into account at the design stage, and specify the fill, condenser and other components accordingly, so that the equipment resists scaling and delivers better heat transfer efficiency.