Roscrea Waste Water Treatment Plant

Location:

The Roscrea WWTP is located on the outskirts of Roscrea.

Facility Function:

The treatment plant process effluent from the town of Roscrea. It uses a more passive design to reduce the BOd of the effluent versus the more common aeration method. It has an anerobic digester that uses the sludge to produce biogas. This biogas is burnt in a 40kw CHP to produce power fo the plants own use and the heat is used to keep the digester up at the required tempreature. It also uses LPG to keep the digester warm.

Anerobic digester and storage tank.         Combined heat and power gas engine.

Connection Method:

A data logger has been installed at the electricity meter and also at the incoming gas supply.

There are two gas meters, one for biogas one for LPG.

The connection method for the waste water treatment plant data

Annual Energy Consumption:

The current key parameter of the efficiency of the digester plant is the use of LPG. It is currently measured monthly by the refill quantity from the supplier. This data does not give the plant operators sufficient knowledge to modify parameters to increase yield. Biogas production will be a key performance indicator going foreward, now that there will be sufficient detail.

Main Energy Consuming Equipment

Cost and Energy Savng Actions

1. Co-firing of the CHP research study.

The CHP installed in the plant uses all the stored biogas in approximately 30 mins, then shuts off afterwards.  The boilers run intermittently on the biogas and the whole control regime is not well understood. It was designed to use biogas from multiple digesters that are not as of yet constructed. This may happen in the future. There is clearly a need for increased storage to allow continuous running of the CHP in prime electricity price periods. Short terms there is a study being commenced as a final year dissertation to ascertain if it is feasible to co-fire the methane with propane to allow for a better running regime and output of the CHP. It will be economical to run the CHP on either propane or Methane at current day rate prices. The question remains about the investment cost to allow this to happen.

2. Digester Gas Yield Optimisation.

Untill now there has been no real way to determine the yield versus several operating parameters, i.e. operating tempreature, tempreature cycling, feed rates etc. With the installation of the monitoring equipment, it will now be possible to see yield differences vs these operating parameter changes.

3. More to follow

A thorough analysis has yet to be completed, and will happen towards the end of 2007.

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