Chemical Engineering August 2014 - 34

Feature Report
Advanced Control
Methods for Combustion
Advanced control techniques can
raise efficiency and lower pollutant
emissions in industrial combustion.
The capabilities and adoption of several
methods are discussed
Pal Szentennai
Budapest University of Technology and Economics
Maximilian Lackner
Vienna University of Technology
F
uel combustion in engines,
power plants, boilers, furnaces
and other equipment provides
energy for transportation, heating,
electricity and goods manufacturing.
Optimizing efficiency while
lowering pollutant emissions is the
main goal of industrial combustion,
and reaching those goals, coupled
with climate-change issues, have
triggered a great deal of research in
this field. One approach to improving
the efficiency and emissions
performance of a combustor is to
apply advanced control techniques
for both new and existing installations.
This article presents several
methods of advanced control for
combustion, ranging from new diagnostic
techniques to enhanced control
schemes. Key benefits are cost
savings through higher efficiency,
environmental benefits through
lower levels of pollutants, and increased
safety.
Classic versus advanced control
Combustion proccesses account for
85% of global primary energy production
[1-2], from electricity and
heat generation to propulsion in
terrestrial, marine and aerial transportation.
Measures to increase efficiency
encompass the combustion
High level commands and targets
Decision maker
Sensors
Actuators
Process
(with or without feedback)
Figure 1. The concept and components of closed-loop
control are shown here
Fig. 1:
Concept of closed loop control.
process itself, as well as fuel transportation
and storage, and the use of
its outcome (for instance, in cogeneration,
waste heat is being utilized).
Concerning pollutants, measures to
limit or reduce their impact can be
taken pre-combustion, during combustion
and post-combustion. Prominent
examples of these strategies
include sulfur-free diesel fuel, air or
fuel staging and selective catalytic
reduction (SCR) of NOx.
Energy-efficiency and emissions
strategies depend on the ability to
control combustion processes. Classic
combustion controls are based on
temperature (for example, adjustment
of the air-to-fuel ratio by peak
exhaust gas temperature), flame
emissions (such as the detection of
misfiring in stationary engines by
ultraviolet light detection), measurement
of in-cylinder pressure in
engines and measurement of CO,
CO2 or O2 in the exhaust gases.
Advanced combustion-control
strategies generally represent
extensions and improvements to
classical control methods. An advanced
control system has a closed
feedback loop (open-loop control
systems do not have feedback). In
combustion control, a sensor delivers
data to a decision maker, which
34 ChemiCal engineering www.Che.Com august 2014
sends a signal to an actuator for reaction
(Figure 1). Closed-loop control
can steer a process better than
one using an open-loop system [3-
4]. This article focuses on advanced
sensors and decision-maker algorithms,
because these control-system
elements have seen explosive
development in the past two decades,
whereas valves and actuators
have changed comparatively
little over that time. For more information
on the fundamentals of
process control, see Refs. 5-6.
Advanced combustion control can
be applied to virtually all types of
combustors, including the following:
gas turbines, furnaces, boilers and
reciprocating internal-combustion
engines, to name a few. Often, it is
possible to retrofit existing installations
so that significant economic
and environmental benefits can be
achieved [7].
Modern combustion options
Based on the huge variety of combustion
applications, modern combustion
processes differ significantly
from each other. Distinctions
can be made among combustion
processes of gaseous, liquid and
solid fuels. The two major modes of
combustion are those with the fuel
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Chemical Engineering August 2014

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