Case Studies
Over the last 20 years Air Technology have made some interesting and often surprising findings. Below are a selection of case studies and discoveries that we have made.
Screw Compressor producing no air, but pulling high power
In a very recent survey site had reported that they were running more compressors than they had previously, but production had not increased. They had lost pressure to the factory twice causing loss of product and did not understand why as they appeared to have more than sufficient compressor capacity.
Air Technology noted that there were anomalies in the stage temperatures and recommended testing the machine to confirm its output. On testing the machine was found to produce no air at all and would only make a pressure of 2.6barg. Investigation within the machine revealed the 1st stage dump valve was open, venting all of the air to atmosphere. The actual problem was a corroded bolt on the control air feed to the solenoid. Once rectified the machine performed as would be expected of a machine of its type and age.
The compressor control panel (and the system controller) was showing that the compressor was fully loaded and site cold not understand why they were experiencing problems. A simple hour fix was all it took to bring the compressor back to a working condition. The machine had been running like this for an estimated 5months costing an estimated £12,500.
Centrifugal compressor running at surge limit constantly
One of our engineers conducted a single day survey at this facility. It was noted that the power and assumed flow readings did not tie up. Further investigation with flow and power metering along with interrogation of the compressor panel revealed that the machine was running fully turned down almost all of the time, and was thus, running extremely inefficiently. Performance testing later confirmed this.
On the back of this an entirely new compressor house was commissioned with state of the art compressors and dryers utilising heat recovery. This provided scope for further expansion and a more efficient compressed air system
Screw Compressor stage dump valve open - reducing capacity to 60%
During acceptance testing it was noted that the machine was performing very poorly. Inspection of stage temperatures/pressures revealed a discrepancy and it was revealed that a dump valve was passing from the first stage. The fault was tracked down to a glitch in the software. When rectified the machine tested extremely well.
Wrong gearing on Rotary lobe blower - running at wrong speed
A rotary lobes blower was suspected of performing poorly. Air Technology installed flowmetering and measured the output of the machine and confirmed that it indeed was performing badly. Further inspection revealed that incorrectly sized ratios had been used in the machine causing it to operate at around 1/2 speed.
Extremely inefficient motors
Performance testing a large multistage axial blower, it was noted that the specific power consumption was extremely poor. It was noted that the motors were lo-tech offering a very poor efficiency. This had escaped notice during the purchasing procedure.
Incorrectly working dewpoint meter indicated -70oC PDP, was actually -15oC
On a instrument air that was critical to site operation it was discovered that the site dewpoint meter had been jammed by debris in the pipework. On clearing this and measuring with our own dewpoint meter it was found that the supposedly extremely dry instrument air system was operating on air with a +ve dewpoint. This had caused numerous production outages in the past, costing significant amounts of money. A new dryer was recommended as the old unit was found to be beyond economic repair.
Centifugal machine, surge protection wired incorrectly
During performance testing the blower went into surge, this is not uncommon during testing where tolerances are pushed. However, what was uncommon was that the machine did not detect this and failed to shut down until it was e-stopped. If this had occurred naturally then the machine would have continued to surge until tripping on another parameter. It was noted after testing that all the compressors tested poorly, presumably down to the aerodynamics being adversely effected by periodic sustained surging increasing the tolerances to a large degree. It was subsequently found that the surge protection system had been wired into the wrong ports on the PLC, rendering it useless - this was a common problem across all of the blowers.
Ammonia Control Installation
During one of our projects in the wastewater industry Ammonia control was installed at a site. It was immediately evident that the aeration energy costs had plummeted. The graph below illustrates the energy savings recovered.

WwTW - Case Study 1

1. Identified and repaired fault on the unloading valves of two of the blowers.  These valves were not closing resulting in the blower delivery flow being vented to atmosphere.
2. Identified that all the blowers were running at the wrong speed due to incorrect pulleys being fitted and arranged for the correct pulleys to be fitted.
3. Identified fault on the control system of Tank 2, which prevented the assist blower shutting down at low demand and organised the repair.
4. Identified that the belt drives and tensioning system on the blowers were inadequate and causing excessive torsional vibration.  The controls were modified so that the blowers could be run safely.  It was subsequently identified that the wrong motor mounting plates had been fitted.   

Total energy savings equating to 393,120kWhr per year have been achieved from these actions.

WwTW - Case Study 2
Identified that the control DO meter on MBBR Tank A was reading much lower than the actual DO of 6 – 7mg/l.  The flow to this Tank was over 2,500Nm³/hr higher than the other tanks.   The meter has been calibrated and the flow is now the same as the other tanks. 

This has produced energy savings equating to 604,440kWhr per year.

WwTW - Case Study 3
Identified and reduced the leakage from the passing drain trap on the aeration pipework.  This has produced energy savings equating to 10,580kWhr per year. Early into the investigation the control system was changed such that the one of blowers would shut down during periods of low demand. 

This has produced estimated energy savings equating to 450,000kWhr per year.  

Wind Energy - SW UK
Energy use at this pharmaceutical site in the rural south west of England is made up of electricity for site plant and office operational requirements, natural gas and fuel oil which are used building heating and steam generation process use. Based on 2007 data the site consumes 4,884,995kWh of electricity a year. There are also 122,000litres of fuel oil consumption which equates to 142,740kWh and an additional 116,095kWh of natural use. Half hourly data indicated a site base electricity load profile of ~520kW.

The identified scheme considers installation of 2 number 2 megawatt wind energy generator (WEG) turbines to generate electricity for site demand and export to the grid or other end users. It has been identified that annual site electricity demand is ~ 4.8GWh/year and that potential combined WEG output would be ~7.4GWh/year.

Taking this into account ALL on site demand can be met with notional WEG output with a further ~2.6GWh of electricity being available for export to the grid or potentially a private wire system to other industrial estate end users.

For the purposes of economic appraisal savings identified are calculated based on the combined value of displaced electricity (at 10p/kWh current price), Renewable Obligation Certificates (ROC’s) revenue at £34.30/MWh and the value of grid export electricity which has been estimated at a value of 5p/kWh which is thought to be representative of potential market acceptance.

Two implementation options are recommended for consideration, those being option 1 to enter into a long term design build and operate agreement with a wind energy contract entity whereby a pence per kilowatt hour (p/kWh) charge mechanism would apply and option 2 where the company would realise full capital investment for erection and operation of wind turbines at their site.

There is an identified cost benefit of £155K a year saving for option 1 and £563K per annum saving for option 2 with an estimated payback of 6.92 years against an estimated total capital investment of ~£3.9 million.

Indicative carbon dioxide savings from displaced grid supplied electricity by wind turbine generation output are 3,186.3 tonnes a year.

CHP - SW UK
This company is a multi-national chemical and pharmaceutical business who has an aspiration to deliver a reduced energy cost base whilst reducing their carbon footprint as part of business plan and Corporate Social Responsibility (CSR) objectives. In addition the site has historically experienced unplanned power outages from grid supply resulting in a significant loss of sales; taking this into account the study has also reviewed security of supply as part of potential CHP business need objectives.

Two implementation options have been identified as part of the CHP feasibility study; they are shown below:

Option 1 to utilise a biodiesel fuelled CHP installation 
Option 2 to implement a natural gas fired Spark Ignition Reciprocating engine CHP with heat recovery steam boiler for process distribution.

Both options identified are based on a ~1 MW electrical and ~1.3 MW thermal installation as calculated from average current and future predicted process steam demand at the site.

At the higher level at present only Option 2 would be economically viable as a potential CHP installation technology, which if implemented could deliver a simple payback of ~5.55 years. Alternatively it is estimated that a Third Party Design, Build, Finance and Operate CHP contract would cost ~£84/MWh including gas fuel costs, however at present calculations indicate a net increase in annual costs for the site of ~£75K a year. It should be recognised however that this is an estimated figure and further commercial competitive tender evaluation is recommended.

In summary, overall saving opportunity identified of £149,498 is the product of grid supplied electricity and Climate Change Levy cost avoidance, plus thermal cost avoidance minus gas consumption cost for CHP and maintenance cost for CHP.

Opportunities for Waste Utilisation - Northern Ireland
Option 1 – Installation of a 25 ktpa Dry AD Fermentation Process with CHP Energy Recovery
This option would require installation of a suitable Dry AD Fermentation plant capable of treating up to 25 Ktpa of organic waste input. Appendix 1 details key process inputs and outputs which have been modelled on assumed data and plant performance parameters. At the higher level the plant would typically require a ~ 2 hectare area footprint including upstream waste handling, installed AD's, a CHP unit of ~200 KWe capacity and downstream composting before final disposal offsite. It is estimated that this solution would have a capital cost of ~£1.4 million and achieve saving of ~£302K a year.
Option 2 – Installation of a 45 ktpa Wet AD Process with CHP Energy Recovery
The wet AD option requires upstream brown bin management to achieve appropriate segregated food and kitchen organic waste input through municipal authority combined waste management. The brown bin waste would be collected every week in 25 litre containers from domestic and appropriate commercial sources having a dry solids content of ~3-6%. The key factor in realising a successful project is provision of a homogenous material with modelled plant performance and assumed input
data detailed in Appendix 1. It is estimated that an installation could deliver ~11,549 MWh of electrical output and ~15,000 MWh of thermal output. Estimated digester retention time is approximately 15 to 20 days with mesophilic operation. Capital costs of ~£6.7 million have been identified with annual saving including NI ROC's estimated at ~£1.67 million a year with this figure potentially increasing if planned ROC banding criteria are implemented in 2009 which would give AD technologies 2 ROC's for every MWh of output.
Option 3 – Installation of 2 MW Thermal Biomass Boiler
This option would utilise existing wood waste biomass as a biomass boiler fuel to provide thermal energy to an appropriate site or industrial estate. Appendix 1 provides modelled data based on a fuel input of ~5 ktpa to produce ~17,000 MWh of thermal output. Revenue savings are calculated from an indicative biomass gate fee of £25/tonne for NWP, with the operational user potentially avoiding heating gas costs of ~£690K a year based on a gas cost of 4.1p/kWh.