Hospitals are normally a place we all go when we are in poor health or need of medical intervention, however until now little thought has been given to the effects of poor air quality on the health of staff and patents. Air quality is normally thought about as an outside issue, especially when we think of Internal Combustion Engines exhaust emissions running generators, however this thinking needs to change. Musgrave Generators was contacted to provide a solution to a hospitals poor air quality issue.
The Hospital had identified an issue when staff complained about the poor air quality when the emergency standby generator operated, the offending generator like many critical power generators it is tested periodically with loads between 40 - 60% of its maximum duty along with its emergency backup power role. Running the generator for testing, proving and any emergency power shortages this caused irritating fumes to enter the operating theatre and surrounding areas. Emergency Standby generators are the solution to provide life critical power supply if the electrical grid fails, so are required in many applications.
Why do we need emissions control on generators?
It was identified that the poor air quality was a very possible life critical situation when the generator was running, the issue was present when the generators exhaust emissions were being drawn into the clean air system in the hospital. The ingress of exhaust gas into the operating theatre not only caused irritation but also breached the workplace exposure limits for harmful pollutants, putting both staff and patents at risk of immediate respiratory conditions and complications.
The next stage for the hospital was to undertake air sampling and quantify the issue, the results from the testing backed up the concerns from the staff working in the ultra-clean ventilated operating theatre possibly exceeding Workplace Exposure Limits (WELs). This caused concern when an emergency power out or periodic testing conditions were observed as this would potentially expose people to negative immediate health effects.
Integrated futureproofing – immediate benefit to health
Along with our specialist partner we designed a bespoke emissions reduction system to install on the critical power generator so improving the air quality, enabling the continuous use of the operating theatres with minimum negative effects on the air quality, we set about the task by surveying the site and locating various barriers to the normal emissions reduction solutions. After site discussions with all the stakeholders the opinions matched that a bespoke solution with future proofing would both offer higher emissions reductions but also offer all around reductions of pollutants. The system proposed would reduce the pollutants and the requirement for exhaust silencers, removing one of the barriers to using exhaust gas emissions reduction systems along with reducing an underestimated pollutant noise.
Challenges for retrofitting
The retrofit of exhaust gas equipment can be a challenge when the original exhaust system is designed with high exhaust gas back pressure, installing the emissions reduction unit after silencers is not best working practice unless the system is designed to accommodate it from the initial design. Installing the equipment post silencer can cause issues with engine load acceptance and blockages if the insulation material moves increasing backpressure and reducing the system’s ability to operate at high efficiencies. The increase in back pressure can greatly reduce the generator’s ability to accept load (if a load is applied i.e., the building load this may cause the generator to fail) also the increased back pressure causes a reduced level of oxygen in the combustion process, this raises the combustion temperature and can cause turbo charger and exhaust valve failure. The reduced oxygen levels also increase black smoke or particulate, so increasing the pollution issue.
Forward thinking solutions equals clean air for everyone!
The system designed would require the removal of the two-stage exhaust silencing originally installed, along with installing a supporting framework erecting outside the plant room. This was the most effective way of reducing the emitted exhaust gas emissions, while still allowing the generator to provide 100% duty. The calculations were carried out for both NOx and Particulate matter reductions at both full building load 40-60% and the no load testing conditions, the system was optimized for these load conditions. Cost saving was high on the list so original pipe and framework were used if and where possible.
Ground-breaking designs leading to a cleaner future for all
The design of the emissions reduction system The task of reducing the emission must be broken-down into many stages to ensure extremely high effectiveness of the system, the first pollutant that required reducing are the unburned diesel fumes or Hydrocarbons and the Soluble Organic Fraction in the soot. This is stage is carried out by a platinum group metal coated Diesel Oxidation Catalyst (DOC) the DOC also changes the ratio of NOx =NO/NO2, the increase of NO2 is utilized later in the oxidation of the diesel soot. The Catalyst also carries out other functions in this system, reducing Carbon Monoxide and Aromatic Hydrocarbons. After the gases pass through this section the NOx reduction starts. Urea or AdBlue is injected into the exhaust stream the next stage is to Hydrolyse the Urea solution separating it into its components, Ammonia, and water. The ammonia is used to react with the NOx over a special catalyst later in the process, reducing the Harmful NOx to harmless Nitrogen. The next stage is to reduce the particulate matter or the visible smoke, this is done using a particulate filter. The particulate filter is a highly effective physical barrier to the particles stopping up to 98% of particles sized from PM10-PM2.5. The NOx with the higher NO2 ratio is now utilized in the Oxidation of the Exhaust soot, Oxidizing, or burning the soot in a similar way to a household charcoal BBQ, so the large volume of soot is reduced to a small amount of ash. Finally, the remaining NOx is reduced using the Ammonia, the effective Zeolite catalyst enable remarkably high efficiency over a vast range of temperatures reducing the tail pipe emissions by up to 92%
After installing the emissions reduction system, the generator was run for calibration and a site acceptance test for two days, no pollutants or irritants were detected inside the building in the critical areas. The noise was also greatly reduced allowing widows to remain open during the testing and SAT test. It was commented by the theatre staff that they “did not know the generator was running”, a quite different situation to pre-emissions control.
Pre-install site testing results show that the original emissions samples inside the building were up to three times the workplace exposure limits, placing everyone inside the building at risk, but after the installation of the system when the same testing was carried out to prove the effectiveness of the emissions reduction system the results proved the effectiveness of the system. The results were surprising to the hospital as after a two-hour emissions test run of the generator the pollution levels measured inside the building were zero!
For the first time the operating theatre had clean air with the generator running critical power.
Musgrave along with our specialist have had a small part in keeping staff and patents safe for today and far into the future at this hospital, by ensuring the lights can stay on without people becoming ill from poor air quality.
Please contact our sales team for further information and to arrange a free consultation on 01327 703868 or info@musgrave-generators.com