Environmental Solutions

Ensuring cleaner, healthier air & minimum emission standards compliance and effective air pollution control by reliable environmental solutions.

Our customers throughout Southern Africa rely on John Thompson’s comprehensive range of efficient environmental solutions for air filtration, dust suppression, emission control, gas cleaning and product recovery.

Reliable particulate emission reduction, guaranteed

The Air Quality Act, 2004 defines air pollution as “any change in the composition of the air caused by smoke, soot, dust (including fly ash), cinders, solid particles of any kind, gases, fumes, aerosols and odorous substances”.

To facilitate our customers’ compliance with legislation aimed at protecting people and the environment from the effects of polluted air, we at John Thompson have developed a number of highly effective particulate emission reduction mechanisms. We have signed technology agreements with partners who provide efficient solutions that capture and remove the air pollutant particles right at the point source.

These innovative solutions are all customisable. They are developed by a team of professionally registered engineers, and John Thompson confidently provides guarantees for the emission reduction of systems using these products.

Are you facing an air-quality challenge? Discuss your needs with John Thompson.

Customised emission control design... and more

In addition to our proven design capabilities, we have manufacturing facilities, construction and installation teams, as well as operation and maintenance staff for emission control systems. We also supply spares for John Thompson and certain third-party equipment.

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Environmental Solutions

Pulse Jet Fabric Filters

Pulse Jet Fabric Filters, also known as bag filters, provide high-efficiency air and gas cleaning. Results of less than 10 mg/Nm³ are obtained in the field. Bag filters require higher differential pressure than some of the other cleaning mechanisms.

The dust-tight fabric filter has three sections:

a clean-air plenum at the top
a filtration housing containing a number of cylindrical filter bags in the middle,
and a dust storage hopper at the bottom.

The filter bags are supported by a tube sheet, which separates the filtration housing from the plenum.

Dust-laden air or flue gas enters the collector through a diffuser. The diffuser absorbs the impact of the high-velocity particles, distributes the air and reduces its velocity. The slower airspeed causes the heavier particles to drop into the hopper. The air stream then flows through the filter bags, depositing the fine dust on the outside of the bag. The cleaned air continues upward into the plenum, then exhausts into the atmosphere.

Filter bags are cleaned by momentary, high-pressure back-pulses of compressed air from the clean-air side of the bag filter. These pulses are delivered by blowpipes, arranged over each row of bags. Orifice nozzles in the blowpipes are directed into the centre of each bag. To effectively dislodge dust along the length of the bags, the bursts of air are optimised by venturis, located at the top of the bags.

An electronic sequence controller times the cleaning cycles. A differential pressure (DP controlled) option is available to conserve the compressed air.

Various inlet technologies are employed, depending on the specific application's requirements. Other factors influencing the choice of inlet technologies include limitations on site space. The choice of inlet plays a vital role in determining the performance of a bag filter, so John Thompson performs the necessary engineering studies, including Computational Fluid Dynamics (CFD) analyses to optimise the inlet required.

Off-line cleaning technologies are used in specific cases.

Envelope Pulse Jet Bag filters

Containerised Pulse Jet Bag filters

Reverse Air Bag filters

Reverse-air baghouses are effective for applications involving extremely fine dust where low outlet emissions are required. Bags are cleaned by reversing the airflow through the fabric. This simple cleaning design involves few moving parts. The result: low maintenance, low operating costs and extended bag life.

John Thompson offers two types of reverse-air bag filters:

pressure filters, and
suction filters.

For more information on our two types of reverse-air bag filters, please download this pressure filters and suction filters PDF.

Construction Features

Bag sizes to suit the application
Low-pressure drop
Minimal maintenance
Multiple modular or compartment design
Positive or negative pressure
Pyramid or trough hopper
“Soft” reverse air re-inflation
Temperatures from ambient to 228° C

Wet Scrubbers

Wet scrubbers for air cleaning use liquid to wash pollutants from the gas stream. John Thompson provides four different scrubber designs:

Dynamic scrubber with integral fan
High-efficiency venturi scrubbers
Packed towers for gas absorption
Vaned scrubber with no moving parts

We supply these in several configurations and a range of sizes. They can be constructed in carbon steel, plastics/FRP or exotic stainless steel.

Cyclones

High-efficiency cyclones are the most cost-effective solution for separating dry particulate (10 microns or larger) from gas streams. To keep operating costs low, our well-considered design delivers high efficiency with low pressure drop.

The mechanism of separation is:

centrifugal action of the gas (spinning action), and
inertial separation from the gas (momentum of particles is higher than the gas).

Benefits:

Low initial cost
Low operating expenses
Minimal space requirements
No moving internal parts

System design:

Seemingly a relatively simple device, a cyclone consists of components which must be optimised for the application to work properly together to achieve maximum dust-removal efficiency.

In designing an effective cyclone, John Thompson considers all the forces that dust particles are subjected to simultaneously:

Viscous drag or resistance due to the relative velocity between the carrier gas and the dust particle, its shape and size, and gas viscosity. Each particle must overcome resistance as it moves through the carrier gas stream.
Centrifugal force. This is affected by velocity, cyclone curvature profile and the particulate mass.
Particle inertia, whereby the particle would move in a straight line if not subjected tothe other forces.

Dust Suppression

To control dust generated in a materials handling system, dust suppression systems use the principle of agglomeration.

This process is best described as the atomisation of a water droplet to a smaller size than the dust particle to be captured.

During the operation of the dust suppression system, the dust particles are bombarded with atomised water droplets, typically sized between 3 and 30 microns.

The correct atomisation of the water droplet is critical to the effectiveness of the system, as the water droplet surface tension will repel a smaller dust particle, allowing it to escape.

The smaller water droplets attach to the dust particle, changing its density. As a result, the dust particle becomes heavier and subsequently drops out of the air stream.

The droplet size can be regulated by way of the water and air pressure controls in the main panel.

A typical spray pattern design to cover the mouth of a tipping bay:

Electrostatic Precipitator

Electrostatic precipitators (ESPs), also known as electrostatic air cleaners, use high voltage to charge dust particles for subsequent collection onto collecting plates. The discharge electrodes provide the negative charge which charges the particles. The ESP’s collection efficiency is influenced by the resistivity of the collecting particles and particle size distributions, making these devices ideal for utility coal-fired power stations with consistent combustion and lower power requirements.

The voltage required to charge the particles is supplied by either transformer rectifier sets or high-frequency power supplies. The latter type use high-frequency switching to increase the power supplied to the discharge electrodes, thereby increasing the collection efficiency by up to 60% without increasing the footprint of the electrostatic precipitator.

Flue Gas Conditioning

Flue Gas Desulphurisation

In the combustion of fossil fuels, sulphur is released from the fuel and emitted into the atmosphere. Flue gas desulphurisation (FGD) is the process whereby sulphur compounds are removed from the flue gas of fossil-fuel power stations.

John Thompson, through technology agreements, provides the following range of FGD solutions:

Dry sorbent direct injection system
Semi-dry circulating dry scrubber
Semi-dry systems with rotary atomisers or spray nozzles
Wet systems with lime or limestone
Wet seawater desulphurisation
Day-to-day and outage maintenance services on FGD plants.

Engineering Services

Emission licence requirement services

John Thompson provides design, selection, manufacture, construction, installation, commissioning and operation and maintenance services for compliance with any atmospheric emission licence requirement relating to the above equipment. Our spares department provides spares for the abatement equipment.

High-temperature environments

John Thompson has niche reliable options for high-temperature applications.

Retrofitting to Minimum Emission Standard compliance

John Thompson has successfully retrofitted a number of emission control systems in existing casings, where space constraints have been problematic. These interventions have enabled customers to comply with amendments to the listed activities and associated Minimum Emission Standards as identified in Section 21 of the National Environment Management: Air Quality Act.

Keeping air-quality compliant

To meet changing environmental requirements, John Thompson continually develops and provides products and services in compliance with updated legislation, such as the National Environmental Management Laws Amendment Act.

Enquire Nowabout our Environmental Solutions

Environmental Solutions

Environmental Solutions

Reliable particulate emission reduction, guaranteed

Environmental Solutions

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