Mechanical Technology may 2015

Mechanical Technology — May 2015

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Proactive maintenance, lubrication and contamination management

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ccording to the DEA’s National

Environmental Management:

Air Quality Act 39 of 2004, as

amended according to the Air

Quality Amendment Act 20 of 2014,

solid particulate emissions levels in in-

dustrial environments are reduced to no

more than 100 mg/Nm

from April 2015.

“Unfortunately though,” says Kirsch,

“the Act also makes provisions for

‘exemptions’ and last year Eskom put

in an application for exemptions for all

South African power stations. This appli-

cation was granted on Tuesday February

24, 2015, which means that Eskom is

effectively exempt from meeting nation-

ally binding emission limits for a further

five years,” he reveals. This five-year

exemption period takes the utility to the

2020 requirements, which halve emis-

sion limits again, down to the ultimate

goal of 50 mg/Nm

“The air pollution control systems

Because of Eskom’s focus on the backlog of essential maintenance

on the generation side, the legal requirements for improved emission

control at South African power plants have been shelved for a further

five years.

MechTech

talks to Clyde Bergemann Africa’s Themba

Masimula, senior sales engineer and Jeremy Kirsch, executive

director, about the company’s air pollution control solutions.

at our power plants are failing,” warns

Kirsch, “and anyone can see this from

Google Earth,” he says showing a current

image of the Duvha power station. “I call

this ‘the tail of two stacks’. Half of the

Duvha units have fabric filters, which

work relatively well, while the other half

have electrostatic precipitators (ESPs),”

he points out. Smoke is seen pouring out

of one of the stacks, while the other looks

reactively clean.

“150 mg/Nm

is permissible under

the current license, but few stations

are achieving anywhere near that,” he

suggests, adding that most power sta-

tions with ESPs are emitting more than

200 mg/Nm

on a regular basis. “The

bag filters are running quite well, but at

stations with ESPs such as Tutuka and

Lethabo, all the emission stacks are bad,”

Kirsch believes.

The reasons? “Mostly maintenance,

although the coal quality, with its high

ash content, and multiple-supplier

purchasing policies do not help,” he

responds. “The coal industry has been

opened up, which has lead to wider toler-

ances and more mixed coal quality. This

creates havoc in the furnace and with the

pollution control technologies,” he says.

Clyde Bergemann Africa’s Themba Masimula, senior sales

engineer and Jeremy Kirsch, executive director.

Clyde Bergemann offers proven wet and dry ESP technology which feature:

a low maintenance design with an electromagnetic rapping system located

outside the gas stream; a rigid (Rigitrode

) anode design; and Modulok

collecting electrode plates that overcome distortion for improved plate

alignment and structural integrity.

Clyde Bergemann’s retrofitted pulse jet fabric filters feature: a patented

stepped inlet manifold design for uniform gas distribution and reduce pres-

sure drop; a patented inlet vane system to uniformly distribute gas flow and

reduce bag wear; lower total pressure drop, which reduces I.D. fan power

consumption and operational costs.

Urgent! Upgrading SA’s air pollution systems

Citing a German power station that

receives coal from 124 different sources,

he relates that as each load of coal

comes in, by rail or barge, a sample is

taken and analysed before determining

where to stockpile the delivery. “The

coal is blended to achieve consistency

in terms of calorific value and ash. This

makes it easier to control the power sta-

tion’s output and its emissions. But coal

for Tutuka, for example, is delivered by

1 000-odd trucks per day. This makes it

very difficult to look ahead and manage

the coal quality and consistency. Power

station managers don’t always know

where the coal is from and are faced

with the impossible task of achieving

consistency,” says Kirsch.

ESP upgrades, an interim solution

Describing Clyde Bergemann Africa’s

response to the problem, Masimula says

that well designed and maintained ESPs

should be able to control particulate

emissions to below 100 mg/Nm

. “For

the foreseeable future, we still need to

carry on using ESPs, but we can’t con-

tinue to use the existing units with dated

technology without the quantity of ash

going up the stacks increasing dramati-