Industrial Heating and Residual Heat Emission

Abstract

In the current industrial classification, the classification methods vary with demands. For example, the industries can be classified into light and heavy industries by product purpose and into discrete and continuous industries by mode of production.

4.1 Characteristics and Classification of Industrial Non-Electric Energy Use

In the current industrial classification, the classification methods vary with demands. For example, the industries can be classified into light and heavy industries by product purpose and into discrete and continuous industries by mode of production. To reflect the present situation of industrial heating and residual heat more accurately, we classify industries into two categories based on the characteristics of non-electric energy use for processes in different industries. One is the process industry: Fossil energy is used as fuels and even raw materials to take part in the production of industrial processes, and the energy use in this industry category often has an extremely high demand for temperature and produces rich residual heat resources; The other is the non-process industry: Fossil fuels are primarily used to generate steam, high-temperature hot water, etc. as the heat sources for process, and this category of industry usually has a heavy demand for medium- and low-temperature heat. The specific definitions of the two categories of industries are as follows:

The process industry means the industry using fossil energy as fuels or raw materials, including steel and cement clinker. In the process industry, it is necessary to cool the product stream from the high-temperature reaction or conversion process; therefore, excess heat is discharged at different temperatures to generate rich industrial residual heat resources.

The non-process industry means industry uses hot water and steam as the main heat sources for processes, including food manufacturing, beverage manufacturing, and textile industry. The non-process industry usually has a heavy demand for medium- and low-temperature heat, and hot water or steam is required for heating.

By the above-mentioned definitions, the 31 major manufacturing industries in the Industrial Classification for National Economic Activities are classified, as shown in Table 4.1. It can be seen that the process industry mainly consists of.

Table 4.1 Classification of manufacturing industries

In 2020, the total non-electric energy consumption of the process and non-process industries was about 1.68 billion tons of standard coal, resulting in about 4.55 billion tons of carbon emissions, in which the percentages of the process and non-process industries were 84 and 16% respectively.

4.2 Present Situation of Non-Electric Energy Use and Residual Heat in the Process Industry

The process industry consumes a lot of fossil energy which not only serves as fuel to provide heat for the production process but also partly serves as raw materials to take part in the production, and we cannot merely consider the heating demand. Hence, in this section, both the raw material consumption and the fuel consumption are considered to reflect the consumption of fossil energy in the process industry in a comprehensive manner.

In 2020, the total consumption of terminal fossil fuels in petrochemical, some chemical, nonferrous metal, ferrous metal, and nonmetallic mineral manufacturing was equivalent to 1.41 billion tons of standard coal. The percentages of these five process industries in the total fossil energy consumption are illustrated in the diagram below (Fig. 4.1).

Fig. 4.1

Non-electric energy use structure of the process industry

The non-electric energy use and residual heat potential of major products in the five process industries in 2020 are summarized in the Table 4.2. The theoretical residual heat resources of the process industries amounted to about 11.2 billion GJ, and steel and cement industries had huge residual heat potential:

Table 4.2 Non-electric energy use structure and residual heat potential of major products in process industries (2021)

4.3 Present Situation of Heating in the Non-Process Industry

The present situation of heating in the non-process industry is analyzed based on the China Energy Statistical Yearbook: In 2020, the non-process industry consumed about 8 billion GJ of heat in total, equivalent to about 278 million tons of standard coal and leading to about 710 million tons of carbon emissions. The heating demands were mainly concentrated in some chemical raw materials and chemical products manufacturing, textile, papermaking and paper products, agricultural and sideline food processing, food manufacturing, chemical fiber manufacturing, pharmaceutical manufacturing, wine, beverage, and refined tea manufacturing, and rubber and plastic products. The heating demand of the nine industries accounted for about 79% of the total, producing about 590 million tons of carbon emissions (Fig. 4.2).

Fig. 4.2

Structure of heating in the non-process industry

To better understand the heating demand of the non-process industry, we surveyed the process flows, heat use procedures, and temperature distribution in the textile, papermaking, pharmaceutical, rubber, food manufacturing, and other industries.

For chemical engineering manufacturing falling under the non-process industry, the major products include chlorine alkali, synthetic rubber, polystyrene, and PVC, the main heat use procedures include drying, evaporation, melting, and reaction, and the main temperature demands of heating are concentrated in a range of 150–200 °C.

Food and beverage manufacturing includes agricultural and sideline food processing, food manufacturing, and beverage manufacturing, and under these three major categories of industries, there are such sub-industries as dairy products, sugar manufacturing, meat product processing, and juice manufacturing. The main heat use procedures are evaporation, drying, disinfection, cleaning, etc., and the temperature demands are generally below 150 °C.

For the textile, printing, and dyeing industry, the main process flows include spinning, weaving, printing, and dyeing. The main heating procedures are slashing, cooking, drying, printing, and dyeing, and the temperature demands are generally below 150 °C.

The major products of chemical fiber manufacturing are polyesters, the production process links that use heat directly include the esterification reaction system, the pre-polycondensation system, and the final polycondensation system, and the temperature demands of heating are high, generally above 200 °C.

The main links using steam in pharmaceutical manufacturing include reactive extraction, concentration, and preparation, and the temperature demands are mostly below 150 °C.

The main links using steam in rubber and plastic manufacturing include calendaring, extrusion, and vulcanization, and the temperature demands are concentrated below 150 °C.

The main heat use links in the paper manufacturing industry include bleaching and drying, and the temperature demands are concentrated below 150 °C.

The temperature demands of nine major non-process industries are divided by the temperature demands of the production processes of major products (Table 4.3).

Table 4.3 Structure of temperature demand of heating in the non-process industry

Looking at the heating demands of the nine industries, it is found that 93% of heating demands in the non-process industry at present are concentrated below 200 °C and that 50% are concentrated below 150 °C, which can be met totally by using heat pumps and other low-carbon heat sources. Among them, 26% of heating demands in chemical raw material and chemicals manufacturing are concentrated below 150 °C; in addition, 86% of heating demands in other non-process industries are concentrated below 150 °C (Fig. 4.3).

Fig. 4.3

Structure of temperature demand of heating in the non-process industry in 2020

The characteristics of the chemical industry, food industry, and light industry are as follows: 1. There is a wide range of products, energy use is relatively decentralized, the downstream demands are complicated, and the industrial demands are hard to be quantified with the specific product output; 2. As high-value-added industries, they will be the key components of the added value of the future secondary industry, and the future energy consumption demand may be predicted based on the added value of the industry. Therefore, in this study, the structure of added value of industries in 2050 and the energy consumption per unit of value added are determined mainly with reference to the existing different situations of developed countries and in combination with the future orientation of China to becoming a manufacturing powerhouse. Meanwhile, the key fossil energy alternatives in the industries are analysed, the future promotion rate is planned based on the feasibility analysis, and finally, the industrial energy use in different scenarios is obtained. The final estimates are as follows: The heating demand of the four industries in 2050 will be about 12.5 billion GJ, including about 7.6 billion GJ of heating demand below 150 °C.