classic | mobile
 

Search...

SA Instrumentation & Control Buyers' Guide

Technews Industry Guide - IIoT

Technews Industry Guide - Maintenance, Reliability & Asset Optimisation

 

Optimising the cost of steam generation
January 2012, System Integration & Control Systems Design


Steam has been described as the ‘lifeblood’ of industry. It is the medium by which heat from a boiler is converted into an easily transportable form that can provide diverse services from office heating to the mechanical energy that drives turbine generators. It is still one of the most popular methods of providing an energy source to a process and its associated operations. However, the true cost of generating steam varies from installation to installation depending on how effectively the generation set is optimised and the how the steam is transported through the operation.

It is now well accepted that measuring energy consumption is an important ingredient in the quest to improve energy efficiency. Efficient and accurate metering is vital to ensure that excessive consumption can be detected, along with an accurate picture of where the steam is being used to enable cross-departmental energy charging to be applied.

The rationale for regarding steam monitoring and control as a process is just as valid as monitoring and controlling other parts of the manufacturing process. The more accurate and reliable the measurements that are made, the more informed the decisions that affect costs and product quality. The following is intended to highlight a few areas where for a relatively modest investment; improved efficiencies can be gained quite quickly through the use of the most appropriate technologies.

Steam measurement

A common method of steam metering is the traditional orifice and differential pressure transmitter technique. The main areas of concern with this type of measurement are the orifice plates’ susceptibility to wear introducing immediate inaccuracies, the relatively high pressure losses introduced into the system by the orifice plate and the small measuring range.

Another significant area of potential inaccuracy is the dp transmitter itself, even most so called smart dp transmitters still utilise analogue sensing systems. The primary analogue sensor is very susceptible to drift caused by static pressures and high temperatures. These factors, coupled with the inaccuracies evident at low measuring ranges, can cause the overall performance of the metering installation to be highly suspect. The performance of the transmitter can be improved by considering the Yokogawa DPharp series of transmitters. This series of ‘digital’ sensor transmitters have been extensively performance tested on numerous fiscal installations worldwide and have proven to be accurate and reliable.

Yewflow Vortex

Another approach to steam metering is to consider the use of a vortex shedding flowmeter. The Yokogawa Yewflow vortex flowmeter has been installed successfully in thousands of steam metering installations worldwide for over 30 years. The volumetric accuracy of the Yewflow is better than 1% of reading as opposed to 3-5% of full-scale when compared with the orifice method. Low pressure losses, only two connections to the process and high reliability coupled with zero maintenance are just some of the reasons why this meter has been applied in such numbers worldwide. The meter is available in line sizes from DN15 to DN400 with operating temperatures up to 400°C.

Pressure and temperature measurement

The majority of steam metering is still volumetric. With the output of the boiler measured in tonnes/kg/lbs per hour, any change in line pressure through demand can cause significant errors in inferred mass steam calculations on a volumetric measurement. For example, a 0,5 bar change in line pressure at 10 bar operating pressure will cause a 5% error in mass flow accuracy. The installation of a ‘steam computer’ along with pressure and/or temperature measurements (depending on whether the steam is saturated or superheated) can remove the errors caused by line pressure fluctuations.

Applications can be as diverse as condensate differential temperature control through to simple line pressure monitoring. A comprehensive range of pressure and temperature instruments can be supplied to give an accurate and reliable picture of what is happening in the system.

Fuel oil metering

Fuel oil metering is traditionally the domain of mechanical type flow meters, which can be highly prone to problems of blockage or simple mechanical wear and tear due to contaminants in the system. The mechanical meters also introduce a high-pressure loss in the system, which in turn can increase the transportation costs. A modern alternative would be to consider the Rotamass coriolis mass flowmeter. Some of the benefits that can be accrued by applying this type of measurement on boiler fuel oil metering are:

* High accuracy, typically 0,1% of mass flow for liquid applications.

* Wide measuring range.

* Outputs in kg, tonne, lb etc.

* Density outputs available.

Water flow rate monitoring

The Admag AXF electromagnetic flowmeter can be applied on all conductive fluids over 1 μS/cm conductivity. The meter has virtually no pressure losses with its full bore design and has one of the widest dynamic flow ranges available. The high accuracy of reading coupled with low maintenance requirements makes it a sensible alternative to more traditional mechanical type meters.

Boiler combustion measurements

Precise oxygen measurement is critical for boiler combustion control. To achieve optimum combustion efficiency and reduce emissions, the ratio of fuel to air is critical. Too much oxygen causes thermal losses through the exhaust stack, whereas too little produces unacceptable stack emissions. Customers applying the Yokogawa EXA series of oxygen analysers report extended calibration lifetimes due to the unique robust sensor design. In addition, field sensor replacement times have been reduced to only 30 mins instead of the usual 2-3 hours, a great saving of maintenance time and effort.

Conclusion

The benefit of making improved quality measurements on the boiler process is the recording of meaningful information that can be used to improve the optimisation of the boiler control system. Recording can consist of simple paper-based recorders, paperless devices that store the results on computer media or comprehensive data acquisition systems with full monitoring and logging capability.

Many different types of approach to optimised control can be applied, ranging from the single loop approach to a distributed control system based on an embedded operating system. Typical examples include:

* Three element boiler level control.

* Boiler fuel/air ratio control.

* Drum level pressure compensation.

* Automatic combustion control.

* Master steam pressure control.

Remember, the key to executing a successful control strategy is to start with an accurate definition of the desired result – Yokogawa offer’s consultancy and advice in this area.

For more information contact Johan van der Westhuizen, Yokogawa SA, +27 (0)11 831 6300, johan.vanderwesthuizen@yokogawa.com, www.yokogawa.com


Credit(s)
Supplied By: Yokogawa South Africa
Tel: +27 11 831 6300
Fax: +27 11 831 6350
Email: info@za.yokogawa.com
www: www.yokogawa.com/za
Share via email     Share via LinkedIn   Print this page

Further reading:

  • CIP keeps food and beverage plants working efficiently
    February 2017, Endress+Hauser, System Integration & Control Systems Design
    Endress+Hauser guarantee an efficient process within the standards of quality and food safety.
  • Yokogawa ensures uptime in the mill
    February 2017, Yokogawa South Africa, PLCs, DCSs & Controllers
    Centum VP brings premium uptime and data transparency to the sugar industry.
  • Digital indicator for process variables
    February 2017, Loadtech Loadcells, System Integration & Control Systems Design
    The LT1200 panel-mount process indicator is a precision digital indicator for interfacing to and measuring most process variables. The LT1200 is capable of measuring and processing variables such as mA, ...
  • Yokogawa releases wireless vibration sensor
    February 2017, Yokogawa South Africa, Industrial Wireless
    Yokogawa has announced its ISA100 wireless-based field vibration sensor with quick update data ability and a long battery life. By providing real-time updates on vibration levels in plant facilities, ...
  • Affordable robot kits from RS Components
    February 2017, RS Components SA, System Integration & Control Systems Design
    RS Components has introduced two new robotic ‘bundles’, which contain all of the components required to build a four-axis robotic arm and will bring the efficiency and reliability of robotic solutions ...
  • New topologies for automation systems
    February 2017, Schneider Electric South Africa, System Integration & Control Systems Design
    New topologies made possible by the Industrial Internet of Things.
  • PCS Global solution meets Nampower’s stringent requirements
    January 2017, System Integration & Control Systems Design
    Hopsol Africa specialises in the design and construction of solar power plants, targeting commercial, industrial and private customers, as well as direct feed-in independent power supply plants. The recent ...
  • PSY International screw compressor becomes energy efficient
    January 2017, PSY International, System Integration & Control Systems Design
    Control specialist PSY International recently collaborated with compressor specialist, Air Rotory Services, to create an energy-efficient screw compressor. PSY’s Paul Young believes the key was in using ...
  • Case History 152: Control problems with airflows in flotation banks
    January 2017, Michael Brown Control Engineering, System Integration & Control Systems Design
    I have written quite a few articles specifically dealing with control problems in mineral processing plants that are largely due to poor understanding, and apparently complete lack of concern of control ...
  • Yokogawa Operations and Production Management suite
    January 2017, Yokogawa South Africa, IT in Manufacturing
    Yokogawa’s Operations and Production Management suite of solutions has been designed to bridge the gap between production planning and process control, providing a fully integrated business to production environment.
  • Endress+Hauser guarantees an efficient CIP process
    January 2017, Endress+Hauser, System Integration & Control Systems Design
    The CIP system can be automated to any desired level to keep a plant working efficiently within the standards of hygienic quality and safety.
  • Yokogawa sets up Architecture Development Division California
    January 2017, Yokogawa South Africa, News
    Yokogawa Electric Corporation has announced that it has established the Architecture Development Division California, an organisation that is dedicated to the development of architecture for the industrial ...

 
 
         
Contact:
Technews Publishing (Pty) Ltd
1st Floor, Stabilitas House
265 Kent Ave, Randburg, 2194
South Africa
Publications by Technews
Dataweek Electronics & Communications Technology
Electronic Buyers Guide (EBG)

Hi-Tech Security Solutions
Hi-Tech Security Business Directory

Motion Control in Southern Africa
Motion Control Buyers’ Guide (MCBG)

South African Instrumentation & Control
South African Instrumentation & Control Buyers’ Guide (IBG)
Other
Terms & conditions of use, including privacy policy
PAIA Manual





 

         
    classic | mobile

Copyright © Technews Publishing (Pty) Ltd. All rights reserved.