Variable Speed Drives vary the speed of a normally fixed speed motor and in this way energy can be saved when production is low. Nampak Rigids was interested in installing a VSD on one of their high pressure compressors to realize some energy savings during their off-peak season.
Grey Green managed the project and facilitated the energy measurements before and after the VSD was installed to monitor the energy savings that were obtained. The actual Siemens VSD was installed by ART Mechatronics Lab and overseen by our team.
Grey Green recently completed a comprehensive energy audit at one of the largest tyre manufacturers in Africa. Our team investigated all energy and material flows. Excellent savings opportunities were found on:
Air compressors, plus compressed air distribution and use
Boiler, steam distribution and use
The sixteen best savings opportunities gave payback periods between immediate (no Capex required, just improved control or maintenance) to ~3.9 years, with the average at less than 2 years. These were also quantified in terms of reduced carbon dioxide emissions and decreased carbon tax liability.
Annual financial savings were several millions of Rands.
The tyre company management shall also be able to use our Scenario Planning Tool to:
Graphically compare the savings produced by each savings opportunity
Decide when each opportunity should be implemented
Grey Green also conducted pre-feasibility studies on various sources of renewable energy:
Earth – Biogas, from anaerobic digestion of locally sourced organic matter and biomass as a boiler fuel
Wind – Wind turbines opportunities in the region
Fire – Solar PV (i.e. photovoltaic) and solar water heating
Water – Hydro-electric options available.
As expected, the renewable energy opportunities have longer payback periods than energy efficiency opportunities, but once factory efficiency has been maximised, the only way of reducing energy costs further is by producing one’s own energy from renewable sources.
Grey Green was recently commissioned by Swisscontact as part of their Energy Efficient Clay Brick (EECB) project to complete a detailed Energy Balance and SARS 12L tax rebate case study for improving kiln efficiency by replacing clamp kilns with VSBKs (Vertical Shaft Brick Kilns) at a local brick works. See below for the case study – the savings are astonishing!
Grey Green has investigated the fans at numerous factories, including at several large grain mills. Often dampers are used to control flow rates and pressures. If so, removing the dampers or changing the fan speed produces good savings.
A mineral processing works has six identical, belt driven fans. All operate against dampers which are approximately half closed.
Grey Green calculated that a simple change to the belt drive ratio with fully open dampers would:
Cost approximately R 7 500 to implement (equipment only – installation could be done by the factory’s own maintenance staff).
Produce annual savings of R 173 400 (No typos here the payback period is really only 0.04 years – i.e. less than 1 month).
Another local grain mill has approximately 30 significant sized fans. None have damper control; whenever the mill is operating the fans run continuously at fixed speed.
Grey Green assessed 18 of the biggest fans. Our measurements and calculations showed that many of the fans were far from their optimum (maximum efficiency) operating points – i.e. when plotted on a fan curve like the typical one in the following diagram, their combination of flow rate and pressure rise was far from the best efficiency point.
Due to the age of the fans and their motors we recommended replacement of the worst performers.
For five fans replacement gave payback periods less than 1 year and total annual electricity savings of >R 2 million.
Six more fans could be replaced to produce payback periods between 1 and 2 years, with combined annual electricity savings of R 634 000.
Compressed air systems leak a bit, but not worth worrying about. Right? The shrug and ignore, business as usual approach is common. What a waste of an excellent opportunity to make big savings.
While assessing energy at factory, Grey Green’s engineers where able to measure compressed air leakage rate. Our client kindly agreed to leave all machines except their air compressor off for a few minutes. The photographs show the results.
The compressor is:
• An oil injected rotary screw machine
(by far the most common type used in SA factories).
• Relatively new, and fitted with a VSD (variable speed drive).
The photographs are of the display on the compressor when no other machines were running. The percentages show the speed of the compressor. Since it is a screw compressor, the percentages also indicate the proportion of rated flow rate which the compressor is delivering – an average of 41 %, when nothing else in the factory was on! 41 % of rated flow was feeding leaks!
• A 75 kW compressor supplying air to a system
with the same leakage rate
• Electricity cost of 65 c/kWh
• 2 shifts a day, 5 days a week, 48 weeks a year,
i.e. 3 840 hours operation a year.
• Wasted power = 0.41 x 75 = 31 kW
• Wasted energy = 118 080 kWh
• Wasted expenditure = R 76 750
Cost of locating and fixing leaks? Usually nothing more than time when a maintenance fitter is not busy with breakdowns.
Need help in getting started? Wondering what else could be improved on your compressed air system? Contact Grey Green now.
SARS’s 12 i scheme allows companies to claim tax rebates for capital expenditure which produces energy savings. Several requirements apply. One is a baseline report which shows the energy intensity before installation of the energy savings equipment.
Grey Green compiled a baseline report for a large dairy in the Eastern Cape.
The baseline report met all the requirements and the diary is proceeding with installation of energy savings equipment.
Baseline reports have to conform to the procedures of the IPMVP [International Performance Measurement and Verification Protocol) and SANS 50010 – South Africa’s standard for Measurement and Verification.
Producing the baseline included correlating energy usage with production. The following graphic is an example.
Effect of Production on Steam Usage
Seasonal variations in production and therefore energy are common with agro-processing. For our dairy client these were investigated by first considering how output varies from month to month. The following graphic shows that there is considerable seasonal variation.
Seasonal Variation in Production
Next month to month electricity usage was investigated. The following graphic indicates that it does not change much.
Seasonal Variation in Electricity Usage
In addition to using a baseline report for tax rebate applications, the data will often reveal opportunities for energy savings. For example, comparison of the previous two graphics seems to show a mismatch between production variations and monthly changes in energy consumed.
Grey Green have audited six wineries in the Western Cape during the harvest period over the past few months with another two winery energy audits in progress and a further three in the pipeline.
On average, the energy saving opportunities identified at each site could potentially save the wineries approximately R 370 000 per annum with a promising average pay-back period of 3 years. We also calculated an average of 400 tonnes of equivalent carbon dioxide emissions saved through our recommendations.
Highlights of the proposed interventions included:
Effluent Treatment Optimizations
Feasibility Studies for Solar PV
Waste-Heat Recovery System design
Energy Efficient Extraction System design
Efficient Lighting Retro-fit proposals
Chiller System Optimizations including. insulation
Interestingly, chillers (cooling/refrigeration) accounted for approximately 40% of the total energy consumption, with the exception of those wineries with a distillery. The distillery accounted for 18% electrically and when converting the boiler fuel into equivalent kWh (using the calorific value of the fuel), the fuel accounted for 94% of the total energy consumption!
We have successfully completed a major lighting upgrade program at Peninsula Beverage Company in Parow Industria consisting of 5 sub-projects over a period of more than 2 years and including some 3000 fittings. Every high-bay and fluorescent in the plants, warehouses and offices was replaced with a more efficient alternative. As a result, Penbev are now benefiting from more than R1.1m in annual energy savings and an additional estimate of R270k in demand charge reductions per annum. Grey Green also managed to secure ESKOM rebates for our client in excess of R1.1m to help subsidize the client’s investment in the program.
Grey Green has been appointed by the National Business Initiative to conduct a detailed diagnostic energy audit at a plastics manufacturing plant in Western Cape. This is part of the Private Sector Energy Efficiency program managed and subsidized by the NBI. The audit is expected to take one month and shall be completed by the end June.
Grey Green has been awarded a contract for a major lighting upgrade at Faurecia’s Cape Town operation. The scope of the project includes financing, supply and installation of the new lights, before and after lux level drawings, as well as a 3 year maintenance program. This project shall save our client approximately R 2.5 M over 3 years and is expected to be completed by end June 2014.