Production of Energy from Biomass Residues (Nuts and Fruit Processing Waste)

1. Aim of the Project The aim of the project was to construct a combined heat and power demonstration plant fuelled by agro-food industry residues, in particular: hazelnut shells, olive kernels, fruit stones, pine cone seed wastes, other fruit processing wastes and wood chips.

Photo 1: General view of the plant

2. Introduction The company Energonut srl in Naples has built in the industrial area of Pozzilli this cogeneration plant. The plant construction was completed by the end of 1996 and is operating since early 1997. The fuel material is biomass derived from agro-forestry and agro-industrial activities, such as olive husk, pine cones, hazelnut shells, fruit stones, wood residue etc., gathered inside an area in a range of about 300 km from the power station. The typology of the various fuels, their physical characteristics (calorific value, moisture and ash content etc.) and the seasonal properties of the products required the development of a specific and thorough strategy for purchase and use, specially as every single product needs an individual storage care and mixing conditions. This influences considerably the management of the feedstock supply to the boiler in order to obtain the best fuel mix while at the same time trying to meet very diverging fuel specifications. Italian laws n.9 and 10 of 1991 govern the production and sale of electricity from renewable resources (like biomass) from private operations. The ENERGONUT plant fully complies with the requirements of the above laws and will therefore benefit by the price per kWh for

the electric energy produced by it and sold to ENEL. The electric energy price actually paid covers the production costs of the plant after the significant modifications introduced as suggested by experience.

3. Technical description The project included the design, engineering, construction and commissioning of the complete power station, consisting of the biomass storage yard and handling facilities; the grate steam boiler and flue gas treatment; the turbo-generator and steam condenser, the transformers, switchboards and power connection system to the national electrical network (ENEL); the condenser water cooling system; the ashes recovery and shipping unit; ancillary plants; and the waste heat supply for third party's utilisation (greenhouses, etc.). The steam boiler is equipped with a moving grate specially designed for proper regulation of the combustion rate and a design value for unburned carbon of less than 0.5 %. The ashes (about 200-300 kg/h depending on the fuel mix) are conveyed to an ash silo for storage of 30 m3. The silo is periodically emptied into trucks and the ash is sent to an authorised landfill nearby. ENERGONUT is investigating the possibility to sell the ash as a soil conditioner due to its high potassium content, compost component or cement additive. Natural gas is used as auxiliary fuel for start up and transient phases.

4. Performance of the Plant One of the main objectives was to demonstrate the multi-fuel operation of the boiler since this will give great operational flexibility for this and future plants. Table 1 gives a typical blend of the biomass fuel based on the various types of residues available. The net calorific value, on dry basis, of the fuel fed to the boiler is in the range of 19 - 21 MJ/kg. Photo 2 shows the biomass storage area.

Photo 2: The biomass storage silos

Table 1: Typical blend of the biomass

Type of biomass residue Weight % Olive oil residues 10-20 Almond, walnut shells & apricot stones 10-20 Pine seeds shells and cones 10-30 Other wood residues 50-60

The steam data are summarised in table 2. The electricity production, 70,000 MWh/y, is totally sold to ENEL. The waste heat is available for the customers in the form of warm water at 40 °C. The plant has an annual consumption of 80,000 t/y of biomass fuels corresponding to 36,000 Toe saving. The net rated power output is 9.8 MWe. Figure 3 shows a general view of the plant.

Table 2: Steam data and steam turbine performance

Steam data Steam turbine Steam output 43 t/h Steam generation 43 t/hSteam temperature 505 °C Exhaust steam rate to condenser 38 t/hSteam pressure 67 Bar a Nominal output power 11,000 kWPrimary fuel consumption 8-10 t/h Total plant efficiency 28-29 %Boiler efficiency 94.3 % Net power delivery 9,800 MW

Photo 3 : General view of the installation

During the commissioning of the plant several tests were made with various feedstock mixtures in terms of their quality and of the moisture content. A significant data basis has been established on operating performance with several feedstocks, their characteristics, the transport properties as well as their combustion efficiency. This data basis has been used to improve and optimise the operational status of the plant and to introduce specific and necessary experience based modifications. It has been necessary to make equipment modifications and operational adjustments for the fuel preparation and feeding system, the combustion system and the cooling towers. Before these modifications the plant was operating at significantly reduced availability of about 50 %. After the modifications were completed the availability was improved to 90 % of the rated value. The operators plan to reach the 100 % operational capacity by optimisation in several areas of the plant with emphasis on the feedstock handling, preparation and feeding. Considering the complicated nature of the feedstocks, these problems are understandable. This concept can be disseminated in several countries with similar biomass and agricultural residues especially in the Mediterranean area such as Spain, Portugal, France and Greece.

5. Economic Performance As the plant has reached its full operational capacity only since 1999, it is not possible to have sufficient data concerning its economic performance. However, the total amortisation of the investment is estimated to be completed over the first 8 years of the operation of the plant during which ENEL will buy the exported electricity at subsidized prices. In the same period possible additional income may be gained from the sale of waste heat and the high potassium content ashes which will significantly improve the economic viability of the plant. The useful life time of the plant is estimated to 25 years.

6. Project Identifiers

Project: BM/496/93 Owner: ENERGONUT Srl Via Privata D. Giustino 3/A

80125 Napoli Italy Tel: +39-0865-911028 Fax: + 39-0865-911777

Contractors: SITICEM Spa of Pisa & BABCOCK ENTERPRISE, Group CNIM-Paris.

Technology: BABCOCK ENTERPRISE Total Cost: 21,340,000 ECU EC Support: 2,118,135 ECU