POWER December 2016 - 18

Boiler Cleaning with
Shock Pulse Generators
Increasing plant efficiency and reducing
maintenance costs is important for economic
power plant operation. One part of
the task involves keeping the boiler heating
surfaces as clean as possible, which
increases heat transfer, reduces maintenance,
and avoids unplanned standstills of
the plant. Shock pulse generators (SPGs)
are an innovative and efficient way to
manage boiler cleanliness.
SPGs-developed and produced by the
Swiss company Explosion Power GmbH-are
online boiler cleaning devices that produce
automated shock pulses through the ignition
of pressurized gas mixtures. The area
of application covers various steam generator
designs and a variety of solid fuels. SPGs
can thereby be utilized from the combustion
chamber/first pass-the hottest zone of the
steam generator-through the radiation and
contact passes, up to the coldest steam generator
zones in the economizer.
Plant operators have confirmed significantly
longer uptime for steam generators,
higher efficiency, and longer operational
lives for the steam generator tubes, resulting
in a sustainable and economic plant
operation. Some leading plant suppliers
have chosen to install SPG technology in
new plants in order to additionally benefit
from the equipment's modular system configuration
and compact design.
How Shock Pulse Generators Work
The SPG system consists of the following
components (Figure 1):
■ SPG mounted on the steam generator
wall.
■ Control cabinet connected to the distributed
control system (DCS).
■ Pressure control stations, which reduce
the gas cylinder pressures of the natural
gas/methane (CH4
), oxygen (O2
), and
nitrogen (N2) to 40 bar (580 psig).
■ Valve panel installed as a pre-assembled
module.
With SPGs, the automatically triggered
combustion reactions take place outside
of the steam generator in a stable, pressure-resistant
container, and the generated
pressure wave is passed through a
convergent-divergent nozzle into the steam
generator. The pressure wave generates a
structure-borne sound oscillation within
the caking and sets the flue gas flow and
the heating surfaces into a short-term vibration.
Soot buildup is efficiently cleaned
away through these simultaneously occurring
effects. The penetration depth of the
shock wave depends on the type of device,
but it can be more than 10 meters (m).
Figure 2 shows the sequence of events
during a typical cycle. The steps are:
1. During its waiting time, pressurized ni1.
System overview. Pressurized natural gas/methane (CH4) and oxygen (O2) are reduced
and fed to shock pulse generators (SPGs) via a valve panel when triggered by the controller
to initiate a cleaning cycle. Nitrogen (N2) is used to hold the piston forward during rest
periods. Source: Explosion Power GmbH
Pressurized air
Nitrogen
Oxygen
Control cabinet
(multiple)
Distributed control system
data connection
trogen holds the freely moving piston
forward in the SPG, sealing the outlet
gas-tight.
2. After being enabled by the controller,
the dosing container is
filled to the
set pressure with the necessary small
amounts of natural gas and oxygen. At
this point, the two gases are still completely
separated from each other and
are therefore noncombustible.
3. The transfer solenoid valves for natural
gas and oxygen open, and the two
gases flow into the combustion cylinder,
where they mix with each other and
become combustible.
4. The glow plug is energized, triggering
combustion. Due to the sudden pressure
increase in the combustion chamber to
350 bar, the piston shoots backward,
opening the outlet.
5. The pressure wave passes through the
outlet nozzle into the steam generator
and spreads out-initially linearly and
then spherically.
6. After the pressure wave has left the unit,
nitrogen pressure pushes the piston forward,
closing the outlet. A waiting period
follows, which can last for several hours.
The SPG can be mounted either horizontally
on the steam generator wall (Figure 3)
or vertically on the ceiling. Supplying gas to
the SPG can be easily accomplished using individual
cylinders or small bundles. The piping
to the SPG requires only a 12-millimeter
nominal diameter and a line pressure of 40
bar. A small compressor can also be used for
natural gas with an existing main connection.
The generators have been used in existNatural
gas
to other
Gas pressure
regulation units
shock pulse
generators
Valve panel
Shock pulse
generator
Boiler
inlet
ing plants as a replacement or supplement
for previously installed boiler cleaning technologies.
But another big advantage can be
realized in new construction projects. SPGs
allow a significant reduction in the enclosed
building volume, and thereby the steel required
for construction, compared to plants
designed with long retractable sootblowers.
The cost savings can be substantial. The low
construction volume of approximately 1 cubic
meter per generator even makes installation
in out-of-the-way spaces possible.
Gas supply
storage
Successful Installations
The Werdohl-Elverlingsen coal-fired power
plant in Germany is operated by Mark-E, a
subsidiary of the ENERVIE Group. Block E4
has an electrical output of 321 MW. The
unit has a Benson steam generator with
18
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POWER | December 2016
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POWER December 2016

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