FOULING IN HEAT EXCHANGERS

marzo 22, 2022

FOULING IN HEAT EXCHANGERS - MAINTENANCE

Fouling is the formation of unwanted material deposits on heat transfer surfaces during process heating and cooling.

It occurs in all industries and heat exchanger designs, with impacts ranging from heat transfer degradation to flow resistance and pressure drops. By forming a kind of insulation on heat-transfer surfaces and reducing heat transfer, fouling undermines heat exchange efficiency

COSTS OF FOULING

Fouling prevention for heat exchangers is typically focused around the heat exchangers itself, however the fouling and heat exchanger performance can be affected by system characteristics that are present both before and after the heat exchanger. These characteristics can include varying product properties, product handling prior to the heat exchanger and operational performance of other equipment, such as pumps, valves and back pressure.

In short, the costs of fouling are many and varied.

Production inefficiencies from pressure drops and poor heat transfer
Maintenance time and equipment for removal of heavy fouling deposits
Cleaning equipment & chemicals
Hazardous cleaning solution disposal
Reduced service life and added energy costs
Production loss from shutdowns
Replacement of plugged equipment
Decreased regeneration efficiency

TYPES OF FOULING

The most commonly occurring types of fouling and aging in hygienic processing fall into four main types:

Incrustation: the accumulation of a crust or coating of processed fluids, minerals, or cleaning agents on the surface of heat exchanger parts.
Scaling: a type of incrustation caused by calcium carbonate, calcium sulfate, and silicates.
Sediment: comes from corrosion products, metal oxides, silt, alumina, and diatomic organisms (microalgae) and their excrement.
Biological growth: Sources of biofouling include bacteria, nematodes, and protozoa.

CAUSES OF FOULING IN HEAT EXCHANGERS

several variables contribute to fouling, including water pH, product viscosity, and the roughness of component surfaces, among many others.

Together, the variables can be expressed as a fouling factor that numerically represents resistance to heat transfer — or thermal resistance — in your system.

KEY FOULING FACTORS

Dairy applications include fats, sugars, and proteins that contribute to fouling. In food and beverage applications, particulate matter can clump and clog, and in pharmaceutical applications, cosmetic and pharmaceutical particles produced during processing can stick and accumulate. To help control fouling, operators pay attention to four key processing factors:

Fluid velocity
Fluid temperature
Fluid chemistry
Materials of fabrication

HOW TO DETECT FOULING IN HEAT EXCHANGERS

Fouling detection typically occurs by physical inspection or by monitoring system performance.

Physical inspection includes measuring the fouling's thickness on plates, pipes, or tubes.

Heat transfer: because of the insulating properties of fouling, heat transfer can fall outside of operating specifications.
Pressure drop: Pressure drop increases between heat exchanger inlet and outlet may indicate frictional resistance or blocked flow paths caused by fouling deposits.

Monitoring temperature and pressures are the best way to troubleshoot and detect fouling in heat exchangers. Instruments measure and report critical variables that can indicate heat exchanger fouling.