Evaluation of environmental and energy effects of biomass district heating by a wide survey based on operational conditions in Italy

Highlights

• We analysed the state of the art of biomass district heating in Italy.

• We provided a database and calculated energy, environmental and economic indicators.

• We resumed the outcomes by tables and graphs.

• We underlined strengths and weaknesses of the set of plants.

• We provided suggestions for the evolution of these plants towards low carbon scenarios and 4GDH.

Abstract

The research aims to evaluate the technical features and the performance of a large sample of biomass district heating plants (BDHP), mainly located in northern Italy and fuelled by wooden chips. These plants have determined the development of a local energy supply chain based on forest by-products, as an alternative to traditional fossil fuels. Main strength of the research is the representativeness of the sample (65 plants of different size and features) and the reliability of data collected. After a deep desk research, data were collected by a questionnaire and then refined and elaborated by an Excel database. Energy, environment and economy indices and indicators were calculated. Despite the large range of variation of results, the following improvements and drivers can be defined: reduction of heat losses between heat generation and final users; optimization of the matching between heat demand and supply during the day and taking into account the winter or summer operative conditions, and, in a smart district heating framework, integration of other renewable sources, cascade use of heat, cogeneration and district cooling (where needed).

Introduction

District heating appears in Europe at the beginning of the 20th century and currently 4174 district heating plants (DHP) are in operation for a total coverage of 10% of the heating market, fuelled also by renewable energies and waste heat. Many researchers have focused their studies to investigate this field, underlining the important role of DHP in order to match the European targets defined for the following decades [1].

In Italy district heating networks are mainly distributed in the northern part and permit to satisfy about the 5–6% of the total heat demand [[2], [3], [4]].

In 2016 the Italian DHP were about 236, with a total thermal capacity of 8,727 MW. This power includes 3,705 of basic power and 5,022 MW of backup thermal power; 1,209 MW, about one third of the basic power, are provided by CHP (combined heat and power). Presently the most part of these plants is fuelled by fossil fuels [3]. Italian biomass district heating plants (BDHP) are the focus of the present research. They are around one hundred for a total thermal power of about 614 MW (considering only biomass boilers) and are mainly located in the mountain areas of northern Italy. The Italian BDHP include small sizes (thermal powers < 1 MW), medium sizes (thermal powers from 1 to 6 MW) and relatively big sizes (thermal powers from 10 to 20 MW and more). Our survey evidences that the majority of the plants are characterized by a small size, suitable with the approach that enhance the sustainable use of the resources locally available [4].

Despite of the many barriers related to the regulatory, administrative and economic difficulties, district heating (DH) based on renewable sources and use of waste heat is increasing [3], with many effects related to the relationship between people and their territory [4].

In this framework, BDHP have considerable importance, in fact forests cover about one third of the Italian territory giving a wide spread availability of wood derived from maintenance activity and as by-product of timber industry.

The design of a BDHP represents an important project of local energy planning and as an interesting investment for the territory. The characteristics and dimensions of BDHP depend mainly on biomass availability in the surroundings, climatic, morphologic and orographic conditions, availability of users and regulative framework in force. Several benefits can be achieved: to use properly an available renewable sources, otherwise not exploited; to contribute in reaching energy target about thermal uses [4,5]; to support the local forest-energy chain that can be even combined with territorial agricultural activities [4,6]; to reduce the penetration of imported fossil fuels, where not precisely convenient; to mitigate the environmental effects related to fossil fuels exploitation; to foster the accomplishment of underground infrastructures (e.g. broadband connection); to improve the protection of the territory, reducing the risk of flooding and landslides; to promote the development of local economies, reducing the risk of abandonment of territories economically depressed.

These issues have been investigated in several recent researches such as [[7], [8], [9]]. In particular, [7] underlines that, despite the institutional framework and regulation vary between the different countries and cultures, in general, the primary motivation for developing DHP is security of supply and replacing oil with various local and/or cheaper fuels. Referring to the long lasting Danish experience on this framework, the authors of [8] conclude that the best solution for providing heat in the future is to combine a gradual expansion of district heating with individual heat pumps and to implement a gradual technological improvement. Moreover, [8] underlines that the expansion of district heating will help utilize heat production from waste incineration and industrial excess heat production, biomass, geothermal and solar sources. In Ref. [9], the authors underline the variability of legal frameworks and pricing principles among regions and countries for DH.

As other energy sources, biomass have to be used properly and effectively [6]. Therefore, the real operative conditions of a large sample of Italian BDHP are investigated in order to verify accurately the produced effects. The research shows great room of improvements of the operative conditions, highlighting the need to focus on heat storage, heat losses and energy sources integration, key elements for the generational shift [7,8]. This issue is very challenging as demonstrated by interesting recent researches. As example, [7] provides a precise description of the technological evolution of DH all over the world and define the concept of 4th Generation District Heating (4GDH) including the relations to district cooling and the concepts of smart energy and smart thermal grids. Furthermore, the development of 4GDH involves meeting the challenge of more energy efficient buildings as well as being an integrated part of the operation of smart energy systems, i.e. integrated smart electricity, gas and thermal grids. Also [9] underlines the necessity to enhance the current district heating technology to align with future conditions associated to renewables and buildings with low heat demands, introducing again the 4GDH technology. The authors of [9] conclude that district heating and cooling systems have strong potentials to be viable heat and cold supply options, but more efforts are required for identification, assessment, and implementation of these potentials in order to harvest the global benefits. In Ref. [10], focusing in particular on a case of large-scale DH in Tallinn (Estonia), the barriers faced by existing DH systems in the transition process towards the 4th generation are reviewed, allowing to assess the main dynamics, as well to focus on the characteristics of DH systems, which need to be improved. In Ref. [11], the evolution of DH also towards 5th Generation District Heating and Cooling Networks is described, underlining the relation with the evolution of buildings and consumers and the need of analysing the flexibility and optimization potential of these networks for a given urban district.

The present research origins in this framework, with the first aim of analysing the state of the art of Italian BDHP, their effects and potential evolution. The study was supported by Fiper¹ (the Italian federation that involves the most part of the Italian biomass district hating plants) in order to clarify the actual performances of the associated plants towards the stakeholders involved in the overall chain.

The effects of the BDHP are investigated taking into account the so called “3E” approach (Energy, Environment and Economy aspects). In particular, the issues of energy efficiencies, thermal renewables integration, impacts on climate change and air quality have been faced. Conversely, the economic effects will be better explored as further developments of the work.

Final considerations about the lessons learned will be provided in order to give guidelines for future energy policies at district, municipal and regional level.