TECHNICAL AND ECONOMIC ANALYSIS OF AN ENERGY EFFICIENCY INTERVENTION WITH INSTALLATION OF A PELLET-POWERED BOILER
Premise
The efficiency project presented here is related to the modification of a thermal power plant by replacing a methane boiler with a pellet-powered boiler.
The efficiency project involved the site of the residence for the elderly “Il Roseto”, a health facility that houses 56 patients and is based in Avellino in a five-storey building above ground for a total of 8,400 m3 to be air-conditioned.
The thermal power plant serving the property is designed to provide both domestic hot water and winter heating. The power plant that existed before the efficiency operation consisted of a 380 kWt boiler, which fed the heating system, and an 80 kWt boiler, which fed the domestic hot water system. In addition, it had a third boiler of 320 kWt, not in operation, which was supposed to power an adjacent building later disused. The following photos detail the status of the plant before the efficiency intervention:
DESCRIPTION OF THE PROJECT
The efficiency project started from a careful analysis of the real consumption of the structure and its real demand for thermal energy for heating and for the production of domestic hot water. The Analysis was carried out both by analyzing the invoices for the supply of methane and by making an energy diagnosis of the entire building in relation to the real conditions of use.
The energy diagnosis showed that the existing thermal power plant was oversized compared to the real needs of the structure. In fact, the calculations carried out showed that the overall thermal energy requirement could be met by a single pellet-powered 300 kWt boiler and by making appropriate changes to the architecture of the plant in order to improve its efficiency.
The main condition to be respected in the realization of the project was the absolute absence of interruption of the operation of the plant in order to avoid any discomfort for the guests of the structure. Therefore, the first phase of the project inpredicted the reactivation of the 320 kW boiler, bringing it back to perfect efficiency. Subsequently, the 380 kW boiler was removed and the CA base was made to bear the load of the pellet-powered boiler. Subsequently, changes were made to the hydraulic circuit of the plant necessary to allow the correct operation of the new boiler, with the possibility of leaving the two existing boilers operational as emergency boilers to be used during the maintenance of the new boiler or, in the event of the absence of pellets.
The photo below details the status of the plant after the efficiency operation. It can be seen that the size of the pellet boiler (of 300 kWt) is considerably larger than the methane boiler (of 320 kWt). On the left of the photo, in blue, you can glimpse the presence of an inertial tank of the volume of 2500 liters inserted in order to improve the efficiency of the system and consequently to reduce consumption by optimizing the operation of the boiler that, will no longer be controlled by the water temperature of the heating system but, by the temperature of the water present in the inertial tank that in turn feeds the heating system. In this way, the time to reach the temperature of the radiators is zeroed because, at the time of ignition, within just 5 minutes. all radiators have reached the operating temperature.
Another important aspect in the realization of such a project is the management of pellets, starting from the availability on the market and ending with the management of storage.
Before starting the project, a study was carried out on the availability and costs of pellets in the areas where the plant insists. It should be said that in southern Italy the use of large biomass-powered power plants (pellets) is still very limited, instead small pellet stoves /boilers entrusted to the management of the individual user who buys the pellets exclusively in 15 kg bags can also be found in shopping centers. It is evident that the management of pellets for the supply of large power plants is absolutely different from the management of pellets for feeding small boilers. In fact, the first aspect to be taken care of is the quality of the pellets because, the large boiler manufacturers, at the time of the order, make a commitment to feed the boiler exclusively with certified Class A1 pellets (pure wood pellets) penalty, the forfeiture of the warranty and the loss of the parameters established by the emission legislation. A large pellet-fired power plant requires the need to install an external tank in which sufficient quantities of pellets are stored to power the plant for at least three weeks. The size of the tank must be determined according to the power of the plant and the availability of the pellets in the territory in which the plant insists.
In the specific project illustrated here, the installed tank can contain up to 11 ton of pellets, sufficient for an average duration of three weeks of operation of the plant during the maximum utilization period (15 Nov – 15 Apr in Avellino). The photo below depicts the tank installed at “Il Roseto” in Avellino:
The pellets are supplied in a 1400 kg big bag. The big bags are hoisted by a crane truck on the tank, where there are three loading vents.
Pellet certificates are provided at each discharge. The supplier identified is a supplier operating in the territory based in the Province of Salerno. Normally, in order to obtain the best supply price, given the annual quantities provided for large plants, a framework agreement with an open order is signed with the supplier.
Normally, from the moment of ordering, the pellets are unloaded within five working days. To date, the plant installed at “Il Roseto”, has never been stopped due to lack of fuel.
SPECIFICATIONS OF SUPPLY
The new biomass plant consists of a Viessmann brand pellet boiler model KOB 300 of 300 kWt, an inertial tank of 2500 liters brand Cordivari and a tank for the storage of pellets of 17 m3 (11 Ton) brand MAFA (Sweden) model SUCCE’ BIO.
Maintenance
A pellet-powered boiler does not require special maintenance. In fact, a large pellet boiler is a boiler normally controlled and monitored through a series of sensors and photocells that monitor all operating parameters and parameters related to emissions into the atmosphere. The monitoring is of the continuous type and takes place through an electronic control unit (supplied by the manufacturer). With the installation of a special system, the boiler can also be monitored remotely.
The type of ordinary maintenance is therefore, aimed at the constant removal of ash. These activities are scheduled and take place in accordance with the provisions of the use and maintenance booklet provided by the manufacturer. The cadence of interventions is on average every 300 hours, 600 hours and 1000 hours of operation. Ordinary maintenance interventions can also be carried out by non-specialized personnel because they are mainly cleaning interventions. Any failure interventions must necessarily be carried out by the manufacturer’s service center.
For the above, the costs for routine maintenance are very low. The senior residence “Il Roseto” has entered into an annual ordinary maintenance contract for € 3,000.00. To date, no extraordinary maintenance has been required.
AUTHORIZATION PROCEDURE
Normally, the modification of a thermal power plant is authorized by a simple CIL if no interventions are required that change the volume of the building. But, even in the case of any volumetric changes, since the thermal power plant is a technical room, most municipalities authorize intervention with a SCIA.
IMPLEMENTATION TIMES
In the absence of special authorization procedures, the installation and commissioning of a pellet-powered boiler takes a maximum of six months from the signing of the contract to the issue of the certificate of acceptance by the competent bodies (INAIL) and VVFF.
ECONOMIC AND FINANCIAL ANALYSIS OF ASSISTANCE
The residence for the elderly “Il Roseto”, before the efficiency intervention had a cost of methane for heating only and domestic hot water of 29,312 €/year for a consumption of 37,967 smc (as shown in the table below).
Making a simple calculation, to produce the same energy, but with pellet feeding, it would have taken 75,934 kg/year of pellets. Therefore, even from the simple comparison of the two fuels, the considerable savings (about 30% less) in economic terms were evident. Adding to these numbers, the greater efficiency of the pellet-powered plant compared to the methane-powered one, achieved an estimated return on investment over about 7.5 years.
With the support of this data, the Board of Directors of the “Roseto”, decided to carry out the transformation of the thermal power plant.
DESCRIPTION OF THE FINAL DATA
Below are the real consumption data obtained from a match of the costs actually incurred in the first two years of operation of the new boiler:
Year from 1 July 2017 to 30 June 2018
During the period under consideration, 6 detailed pellet loads were carried out in the following table:
Comparing with the pellet consumption figure provided for in the economic and financial plan of 75,934 kg/year, there is a saving of about 40% that in economic terms is realized in a saving of about 32% considering that proportionally, for the purchase of 75,934 kg of pellets a total cost of about € 19,742.00 would have been incurred compared to the 13,426.00 Euros actually spent.
Year from 1 July 2018 to 30 June 2019
During the period under consideration, 6 detailed pellet loads were carried out in the following table:
Comparing with the pellet consumption figure provided for in the economic and financial plan of 75,934 kg/year, there is a saving of about 40% that in economic terms is realized in a saving of about 33% considering that proportionally, for the purchase of 75,934 kg of pellets a total cost of about € 20,122.00 should have been incurred compared to the 13,443.00 Euros actually spent.
The best result is mainly due to the fact that the energy efficiency of the existing plant provided for a new calculation of the actual thermal power that the building needed for the same internal climatic conditions. The new calculation showed that in the face of a 380 kWt boiler for heating and an 80 kWt boiler for the ACS it was sufficient to install a single 300 kWt boiler that, connected to a thermal flywheel, provided for the heating and production of ACS. The facts have shown that the efficiency project has been fully successful, allowing less time for the return on investment than initially estimated.
In fact, if initially the return time of the investment was estimated at 7.5 years, the reality has shown that the return time of the investment, in the absence of any state contribution, is equal to 5.5 years.