How to enhance process efficiency and profitability by new controlling technology

How to enhance process efficiency and profitability
of water treatment systems in cooling towers
by new controlling technology
White Paper
March 2009
How to enhance process
efficiency and profitability of
water treatment systems in cooling
towers by new controlling technology
Dr. Egon Hüfner, Segment Manager Water,
Bürkert Fluid Control Systems
Water treatment systems in cooling towers are dynamic entities that are
subject to numerous factors like varying operating and environmental
conditions, seasonal alteration in water chemistry, and compliance with
tightening environmental regulations. Securing the requested water quality requires continuous control of source water, and permanent surveillance of the treatment process. At the same time, analysis requirements
and compliance with environmental provisions create a growing need
for analysis recording and transmission of relevant data concerning
water output and quality. The automation of water treatment systems
reduces costs. It increases productivity, saves water and energy, and
minimizes the risk of chemical overfeed or underfeed while simplifying
compliance with environmental standards.
Water treatment systems for cooling towers can be controlled manually when
water quality and operating conditions are consistent. Samples then have to
be taken regularly by technicians, who analyse the process conditions before determining the ratio between the supply of fresh water and chemicals
New controlling technology enhances process efficiency and profitability of
water treatment systems in cooling towers
2
required. They adjust the pH, ORP (oxygen reduction potential), conductivity,
alkalinity, hardness, corrosion and other factors. These steps require in-depth
experience as well as time and manpower.
Sometimes however, the initial conditions may not be simple enough: high
personnel costs, scarce and expensive water resources, and inconsistent
water quality may create a need for more than manual chemistry control. This
is where multi-parameter transmitters have recently established themselves.
They are used as inline signal conditioners, sending analogue inputs to PLCs
(programmable logic controllers). However, as global competition increases
for water treatment OEMs (original equipment manufacturers), these companies are driving their suppliers to incorporate multiparameter transmitters into
single-platform, multifunction flexible controllers—reducing controller and instrumentation costs in some cases by as much as 50 percent as well as saving
water and chemical costs.
Maximizing turns:
The increasing concentration
of minerals which is a result of
water evaporation in cooling
towers creates difficulties for
heat exchange processes.
Mineral deposits (scaling) in
the pipes of heat exchangers
affects their heat transfer
performance. Bacteria too can
produce organic residues (fouling), which also compromise
process efficiency. The continual automatic measurement
and control of pH, ORP, conductivity, alkalinity, hardness,
corrosion and other factors
avoid these problems. The
use of an automated controller with integrated networking
capabilities—like Bürkert’s new
multi-channel mxCONTROL
8620—in combination with the
necessary analytical sensors,
valves, flow transmitters and
switch’s, allow a normal conductivity only controlled cooling
tower to go from a two turn system (ratio between water in and
water out of a cooling tower)
Bürkert´s mxCONTROL 8620 can be used in general process and
chemical control applications such as cooling towers or reverse osmosis systems. It saves time and space by allowing parameterization
and data logging of a wide number of control variants via an
SD card slot, Ethernet interface or USB connection
New controlling technology enhances process efficiency and profitability of
water treatment systems in cooling towers
3
to a seven or eight turn system. This increased number of turns means less
water is required to remove the same amount of heat from the plant. Some
water stressed regions have taken note of this and are even offering financial
incentives for plants to upgrade their controller in an effort to conserve water.
The central control unit regulates the feed of chemicals that prevent corrosion,
scaling and fouling processes. Biocides for example are added over a predetermined period of time as determined necessary during an initial water analysis. An example of chemistry cost savings is the Biocide pre-bleed function.
Continuous monitoring and effective control of biocides provide greater protection from harmful bacteria. Biocides preventing legionella, algae and other
bacteria, are added periodically over a 2 week window. It is often the case
when biocide chemicals are added, loop conductivity increases. This being
the case, it is some times beneficial to bleed to a conductivity set point that is
lower then normal. This is called the “Biocide PreBleed Setpoint“. To prevent
bleeding expensive chemicals to drain, an internal interlock prevents the bleed
valve from opening while chemicals and biocides are added to the system
even if high conductivity set points are reached. In addition, a time delay “lock
out“ prevents the bleed valve from opening for a predetermined period of time
after the chemical is added to ensure that the added biocide has maximum
effective contact time in the system to kill all unwanted organics.
Cooling system corrosion is another unwanted expense factor. Accurate pH
and conductivity readings cannot always guarantee a low corrosion environment throughout the system. A corrosion sensor is often connected to the
control unit. If a predetermined corrosion limit is reached, the control unit will
shut down the pH dosing module and energize the general alarm alerting local
maintenance to investigate. In addition, corrosion inhibitor chemicals can be
added based on a feed water ratio automatically.
Automated all-rounder
With the development of mxCONTROL 8620—a state-of-the-art modular multichannel control system—Bürkert responded to the trend for full automation
and cost saving.
By allowing parameter setting of a wide number of control variants via an SD
card, serial interface or modem connection, the mxCONTROL 8620 saves
time, space and equipment costs in cooling towers, as well as in boilers, dead
end and cross flow membrane filtration systems. With the launch of the mxCONTROL, users no longer have to select a model type that fits their specific
application. Instead, via customised software and a standard SD card, the
number of control variants is unlimited, making the mxCONTROL a true “onesize-fits-all” solution.
The mxCONTROL 8620 is specifically designed for seamless integration into
countless chemical or process control applications. Its modular design integra-
New controlling technology enhances process efficiency and profitability of
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4
tes multiple,
customerselectable
inputs and
outputs
(4-20mA,
Pt100,
digital, relay
and transistor), combines these
with various
control
parameters
resulting in
dozens of
flexible conThe mxControl 8620 is capable of processing up to four analogue, two RTD, and eight digital inputs
as well as five relay and four digital transistor outputs and four optional analogue outputs – a total of
figuration
23 I/O (model dependent) – simultaneously
possibilities.
In addition to normal chemistry control, the 8620 can also integrate control of
a large number of traditional process variables such as pressure, temperature
and level, removing the requirement in many automated systems for external
devices to cover the same functions. Understanding the needs of the water
treatment users, and combining these with the processing power of the mxCONTROL, has led to the introduction of intelligent control of the water parameters that significantly reduces waste by avoiding unnecessary or untimely
dosing and bleeding-off.
The flexible control and easy adaptation to processes made possible by the
8620 controller are the result of a high-level software architecture, which enables all standard modules to be easily loaded by SD Card, serial interface or
remote modem. Alternatively, the future possibility of Ethernet can be used to
configure and set the parameters on the controller or down load historical data
saved on the SD card. Local manual interface is also available where an operator can simply set and display all important variables and parameters via five
soft-touch keys. Once this is achieved, sophisticated electronics and state-ofthe-art control algorithms ensure that optimum process control is maintained
at all times with minimal operator intervention. Moreover, operating security
can be tailored to individual applications, with three levels of human-machine
interface available: Open Access, Operator Only Access, or Specialist Access.
The key to this high level, automated control is a 32-bit micro-process controller, supported by an integrated 512 kB flash memory for parameter storage
and additional languages. This enables the mxCONTROL to support up to a
maximum of eight active control loops with minimum sample periods of 100ms
(50ms for 4 active loops). This could involve simultaneously processing of
up to four analogue, two RTD and eight digital inputs, as well as five relay
outputs, four transistor outputs and four analogue outputs. In addition, data
New controlling technology enhances process efficiency and profitability of
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logging and parameterization uploading and downloading is possible via an
SD memory card that fits into the front of the controller via an SD card slot.
The modularity provided by the mxCONTROL is virtually unlimited due to the
unit’s functionality and flexible software configuration possibilities. The primary functions include: Conductivity Control, which features on/off control or
specific set point with PI(proportional integrator)-controlled continuous dosing
through pulses, automatic or manual bleed off; Chlorine/Redox and pH control, both of which offer on/off control, and PI-controlled continuous dosing
through pulses or analogue outputs; Flow Control and totalizing, with K-factoring; and Biocide Dosing over a 14-day program, featuring 8 dosing events for
each of the two channels per day. These are complemented by additional features such as the display, transmission and recording of pressure, pH, ORP,
conductivity, O2, CL2, level, temperature and TDS, frequency filter, password
protection, alarm output, engineering units and an inverse function for on/off,
proportional or PID control.
Safeguarding the continuous operation of the mxCONTROL against the elements is IP65 (NEMA 4X) ingress protection: this is effective when the door of
the unit is closed. Further safeguards are provided by the unit’s rugged screw
terminals and cable glands; and by the 10-year service life of the replaceable
lithium battery which backs up the mxCONTROL’s real-time clock. The controller meets EN 61000 and EN 55011 European EMC standards, the IEC 68
environmental directive, and is CE marked. UL/CSA approvals are pending.
The Bürkert transmitter Type 8202 (left) is a compact and modular device
specially designed for measuring the pH or O.R.P. value of fluids while the
Type 8222 conductivity transmitter has 3 cell constant options for diverse
applications
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Contact
Do you have questions or can we show you our newest
controlling technology? Just contact
Bürkert Fluid Control Systems
Bürkert Werke GmbH
Dr. Egon Hüfner
Segment Manager Water
Christian-Bürkert-Str. 13-17
74653 Ingelfingen
Germany
Phone: +49 7940 10 91 470
Fax: +49 7940 10 91 204
Email: egon.huefner@burkert.com
Website: www.burkert.com
New controlling technology enhances process efficiency and profitability of
water treatment systems in cooling towers
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