Energies 2019 , 12 , 247
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energy efficiency, where SEC is commonly used as an e-KPI. Examples of how many and what type of companies that have been studied in the PPI are 48 pulp and paper mills in Sweden 2006–2015 [6] and 40 pulp and paper mills in Sweden [29]. Examples of other industrial companies that have been studied are 27 foundries in Sweden [30], 65 foundries in Europe ([31,32]), 23 iron and steel mills in Sweden [33], 21 industrial companies in Sweden [34], 11 sawmills [18], and 8 manufacturing firms in Sweden [35]. A database containing data about the use of individual energy carriers and individual pulp and paper products by individual PPI mills in Sweden since 2002 is used, among others studying SEC, for [6]. The rest of the named studies were conducted by collecting data by questionnaires and/or interviews as well as complementing by data from databases in some studies. The results are based on a literature search using Linköping University Library’s literature search system—UniSearch—that was described in detail in Lawrence et al. [36]. UniSearch contains publications that also available through the Web of Science, Scopus, ScienceDirect, etc. In brief, SEC was searched for within those studies that primarily addressed energy management in the pulp and paper industry. Additionally, the snowball method was applied, whereby e.g., publications that referred to other studies using SEC were also included. The literature search was limited to English-language, peer-reviewed, full-text literature accessible via UniSearch in November 2018. In addition to the scientific review, several standards were reviewed in relation to the meaning and usage of SEC as an energy performance indicator: SS-ISO 50001:2011 (energy management systems [15]), SS-ISO 50006:2017 (energy management systems—measuring energy performance using energy baselines (EnB) and energy performance indicators (EnPI) [17]), SS 16212:2012 (energy efficiency and savings calculations, top-down and bottom-up methods [37]) and SS 16231:2012 (energy efficiency benchmarking methodology [9]). SEC in the PPI has been used as an example to illustrate the differences in SEC. The PPI was chosen as an example because it is one of the five most energy-intensive industries globally [3]. In fact, the PPI may account for as much as 5.6% of the global industrial energy end-use [3]. With today’s attempts to achieve a sustainable circular economy, and given the renewable nature of the resources for production, pulp and paper production is likely to increase. Additionally, the PPI is facing challenges in terms of remaining competitive, where the energy efficiency improvement is seen as one of the most effective strategies for remaining competitive in some countries (e.g., [38]). In this study, when needed, primary energy factors (PEFs) and SEC were calculated by dividing the sum of gross electricity produced plus imported/exported electricity, by net electricity used in the country (e.g., [6]). If the SEC in the references was given in units other than the GWh/kt, then the units were converted. Additionally, when the use of energy carriers was given in the references, e.g., use of electricity and heat, then the usage of the primary energy was calculated by using 2.5 as the PEF. PEF of 2.5 means that the generating efficiency for final energy carrier is 40% and implies that 2.5 units of primary energy carriers generate 1 unit of final energy carrier, e.g., electricity. In this study we presented PEF, therefore, if final energy generating efficiency was presented in a reference, such as that the efficiency for generating electricity was 40% in ref. [8], it was recalculated to PEF. In cases where the total energy used was already presented in the references without specifying the PEF used to calculate it, not specified (n.s.) is noted.
4. Results and Discussion
4.1. The Meaning of Specific Energy Consumption (SEC) SEC is a widespread term used by international energy agencies, e.g., [3], and in research studies, e.g., [38]. Nevertheless, energy can only be converted from one form to another or transferred among systems, and cannot be destroyed or created ([39,40]). According to the first law of thermodynamics: “Although energy assumes many forms, the total quantity of energy is constant, and when energy disappears in one form it appears simultaneously in other forms” ([39], p. 22). Thus, energy cannot be “consumed” as such. It is the exergy, i.e., the measure of the quality and quantity of energy, that
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