Advantages of a modern DCS in coal handling

GET WITH
THE SYSTEMRogerio Martins, Schneider Electric, Brazil, discusses
the advantages of modern distributed control
systems in coal handling preparation plants.
| World Coal | June 2014

T
he coal handling preparation plant (CHPP) plays a
key role in the mine supply chain in terms of
meeting customer orders, ensuring the quality of
the coal and managing stockpiles. The control
system used at CHPPs plays a key role in optimising the
processing operations and maximising uptime. It also feeds
data to the manufacturing operations management system to
drive decision making at an enterprise level.
As the ROM coal passes through the various crushing,
washing and separation processes in a CHPP, ensuring the
finished product meets the right grade and size required by
the customer, it requires an automation system to manage coal
flow, density, levels, ash and moisture, etc. These systems
were traditionally managed by a PLC/SCADAarchitecture.
However, mining companies are increasingly looking to
distributed control system (DCS) technology for enhanced
control system functionality and advanced data exchange.
PLC/SCADAsystems are typically very flexible, open and
connect to third party components easily. They are also cost
effective to run. On the other hand, however, there is a low
level of integration, which means operations teams have to
manage many different tools, often from different vendors.
DCS technology was initially focused only on control.
However, it has evolved dramatically over recent years to
become part of global IT. The DCS scope has been modified so
the system receives instructions from enterprise resource
planning (ERPs) and delivers data in return. The technology
also integrates safety systems and fulfills an asset
June 2014 | World Coal |

management role. DCS not only
performs the basic PID loops but also
achieves complex advanced process
control. The system serves as the
operator interface and ensures
operational efficiency. It alerts operators
and is embedded with a sophisticated
alarm management system.
CHPP lifecycles have been affected by
the use of DCS. Several decades ago,
plant evolution was not taken into
consideration when planning control
systems, but these days mining
customers must adapt their production to
meet customer requirements, which
means plants must be expanded or
modified frequently.As technology
evolves quickly, mining companies want
to protect their investment by having a
clear migration path. There is also a need
to consider the impact of emerging
technologies, such as mobile access, as
well as tighter integration into the supply
chain. This increases pressure on control
systems to continue to evolve to meet the
market demands.
As with most mining applications,
control systems in CHPPs must meet the
challenges of system robustness for
continuous use in harsh environments,
near zero downtime and the need for
powerful diagnostics for fast rectification
of any issues. The additional challenge
for CHPPs includes the special process
engineering requirements needed for
particular items of equipment, such as
configuring faceplate commands for
priority control.
Selecting a DCS
Global mining companies usually operate
CHPPs all over the world. They all
process coal, some using the same
methods, while others use different
machinery and procedures that result in
varying throughput and quality. Mining
companies like to standardise and gain
synergies in terms of resources and
maintenance. This enables an operator to
move from one mine to another with
minimal training or, alternatively, an
engineer can be sent to another site to
duplicate an innovation. Common
services should be able to be operated or
maintained remotely. DCS meets these
requirements, as it provides a
standardised environment from mine to
mine and for remote operation centres.
Energy management is increasingly
important for the mining sector, as it
shifts from the mantra of “production at
any cost”, to a quest for more efficient
production. The focus is not purely on
reducing consumption, so metrics such as
overall equipment effectiveness and
energy efficiency (OEE+E), rather than
energy cost or consumption, are
becoming mandatory indicators.Ahigher
degree of focus on sustainability is also
being driven by governments and
stakeholders to control the environmental
impact of operations.
Measuring the energy purchased and
the energy used within the mining
Figure 1. Engineering timeframe comparison.
Figure 2. Benefits for operators.
| World Coal | Reprinted from June 2014

process (as water, air, gas, electricity
and steam) can provide insight into the
efficiency of a CHPP and identify
opportunities where energy can be
saved. By measuring energy using a
DCS, it becomes a manageable input in
the mining process (much like
temperature, pressure, flow, levels,
etc.).
CHPP managers are often required
to do more with less. Operational
efficiency is a consideration when
planning the deployment of a new
system, particularly as the CHPP forms
part of the overall resource to market
operation. This includes what can be
delivered to an operator to obtain the
right information at the right time to
improve the decision making process.
Design considerations
Protection of investment is a major
concern for CHPP owners. When
designing a DCS, project teams must plan
ahead and consider the following:
nn The architecture requirements and
constraints.
nn Any potential modifications that are
required.
nn The project library.
nn Operating data, such as interface
with the ERP and other systems.
The lifecycle of a CHPP must be
considered from the beginning. Adesign
that does not take future modification
into account is not a good one. CHPPs
need flexibility to adapt production to
new customer requests, so scalability is a
key factor. The ability to easily
implement a change request without
revisiting the initial design will make a
difference in the future.
Abig differentiator of DCS over
PLC/SCADAis the standardisation they
provide. In the early stages of design, the
first priority is to define the project
library of objects, such as valves.
Suppliers of valves usually offer different
models of control valves and some even
have an open model that can be
modified to fit their customers’ habits or
specification. Selecting the right model
for all basic objects – and choosing
whether to take a standard valve or build
a new one – will effect not only the
development itself but also the complete
lifecycle of the CHPP.
In terms of hardware and the
flexibility brought by fieldbusses, the
architecture design is key and careful
consideration of the I/O distribution will
impact future maintenance. Agood
design will meet the topology
constraints.
Traceability is also a key parameter to
consider. During the functional design
phase, CHPPs must clearly specify the
data that needs to be tracked, how it will
be stored, how it will be retrieved, and
what kinds of parameters have to be
accessed. In the big data era, the size of
the files is no longer an issue: what is
important is information and how easy it
is to find it.
Engineering with DCS
One of the main benefits of engineering
with DCS is the shorter timeframe to
implement a sequential process
engineering method. The design,
implementation and verification stages
can be consolidated because consistency
is guaranteed by the object oriented
programming, single data entry point
and change propagation features. The
enhanced diagnostics also make the job
easier during system start up.
The consistency of a DCS enables a
reduction up to 30% in engineering time
when compared to the engineering time
to install a conventional PLC/SCADA
system.
Integration is key and engineering
with DCS affects the configuration time,
minimising tests so commissioning can
occur quickly.As most engineers will
know, in the automation world, almost
anything is possible with a little effort.
However, almost every engineer has
experienced the issue of interfacing two
devices using the same protocol, just
because there was a parity difference
somewhere along the line. Project
managers often rank interface as one of
the main reasons for a delay or overspend
on a project.ADCS avoids these kinds of
interface issues.
ADCS offers a database with a
“configure once” philosophy; i.e., there
are no databases to map. For every piece
of data, such as a flow measurement,
Figure 3. The object has all the control and supervisory parts imbedded into it,
including useful information such as documentation, web pages, etc.
Reprinted from June 2014 | World Coal |

there will be a unique identification
throughout the system, both for the
program in the controller, as well as the
symbol on the operator interface. This
tag could be linked to a physical
address and then, no matter what
modifications occur, it will be
completely transparent regardless who
uses the data.
Next generation systems go a step
further, integrating the best of
PLC/SCADA and DCS worlds with
energy management capabilities. This
means that the latest DCS are flexible,
open and easy to use, and combine
integration capabilities, single database
and powerful diagnostics, alongside
energy optimisation, load shedding and
real-time dashboards.
Operations and
maintenance
A CHPP is a continuous process and
stoppages can significantly impact the
coal processing in many ways,
including non-conformance to out-load
plans and poor process performance.
Improved operational intelligence and
simplified maintenance – and therefore
greater uptime – can be achieved with a
good DCS system: i.e., one that enables
operators to quickly and easily navigate
to root causes and rectify any issues.
Basic asset management is now
included in any recent DCS. It gives
operators the minimum information
needed in case of process failure.
A DCS gives a CHPP operator the
ability to navigate easily from one
display to another. The faceplates are
the primary tool. They give the
operator a quick overview of any
process element, allowing them to
pilot the plant with all the process
information needed.
A DCS is usually embedded with
native diagnostics, which means that
an operator can get accurate, real-time
information about any malfunction in
the system, such as why a feeder will
not start. The object library enables the
operator to quickly access manuals,
trend information and understand the
links to other equipment so they can
resolve issues. The latest DCS allow
configuration changes to be made
online without stopping the plant.
Operational and maintenance
efficiencies can be gained for a CHPP,
as a result of greater embedded features
and intelligent data available at an
operator level.
Case study
QingHe coal washing plant is located
in Green River Industrial park in Altay
(in the Xinjiang Province of China)
with an output of 1.5 million tpa of
coal. The main processes in the plant
are non-desliming and non‑pressurised
heavy medium cyclone separation
technology, coarse coal slime recovery
with high frequency sieve and fine coal
slime flotation filter. There are also
workshops for coal washing,
filter press, flotation separation, slurry
concentration and a conveyor belt
corridor. The DCS selected for the
plant was Schneider Electric’s
PlantStruxure process expert system
(PES), which gives the plant object
modelling capabilities and increased
flexibility.
Resolving engineering
challenges with DCS
For this particular project, the challenge
was in the special process requirements.
One of these was the interlock status.
The equipment can also be started or
stopped manually using the popup
faceplate. For any situation, the stop
command on the faceplate should be
given first priority.
Another challenge was the controls.
In the CHPP, besides the group control
(such as raw coal conveying), there
were also some process controls, such
as PID, to control the qualified
medium density. There were also a lot
of analogue variable control processes.
Libraries were the cornerstone of
this project and they were developed to
cater to the special process
requirements, taking into account the
control logic and the human/machine
interface style. The open nature of
PlantStruxure PES enabled third party
libraries to be incorporated into the
system. In the early stages of the project
implementation, the third party library
was modified to fit the requirements of
the coal washing plant before being
integrated into the PES.
Ongoing benefits of DCS
Ongoing maintenance of the plant will
be simplified. This will require fewer
specialised skills and less time, while
the object library can be customised
according to the customer’s standards.
Conclusion
Since they were first launched almost
40 years ago, DCS have evolved from
simple control focused systems to
become an integral part of the
integrated planning and optimisation
solution in a mining operation. The
latest generation of DCS is based on
field-proven hardware and open
ethernet technologies that extend from
device level, through control and
supervisory levels and provide a way
to share information with higher level
operational systems, delivering
intelligence that leads to
operational efficiencies.
Figure 4. Supervision screen of the DCS system.
| World Coal | Reprinted from June 2014

Advantages of a modern DCS in coal handling

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