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Integrated Control of Emission Reduction, Energy-Saving and Cost-Benefit Using a Multi-Objective Optimization Technique in the Pulp and Paper Industry Zongguo WEN, Chang Xu, and Xueying Zhang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/es504740h • Publication Date (Web): 18 Feb 2015 Downloaded from http://pubs.acs.org on February 24, 2015

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Environmental Science & Technology

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Integrated Control of Emission Reductions, Energy-Saving and Cost-Benefit

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Using a Multi-Objective Optimization Technique in the Pulp and Paper

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Industry

4 5 6

Zongguo Wena,*, Chang Xua ，Xueying Zhanga State Key Joint Laboratory of Environment Simulation and Pollution Control (SKLESPC), School of Environment, Tsinghua University, Beijing, 100084 China

7

a

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*Corresponding author: Tel&fax:+86 10 62792921

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Email address:[email protected]

School of Environment, Tsinghua University, China

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Abstract

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Reduction of water pollutant emissions and energy consumption are regarded as key environmental objectives

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for the pulp and paper industry. The paper develops a bottom-up model called the Industrial Water Pollutant

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Control and Technology Policy (IWPCTP) based on an industrial technology simulation system, and

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multi-constraint technological optimization. Five policy scenarios covering the business as usual(BAU) scenario,

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the structural adjustment (SA)scenario, the cleaner technology promotion (CT) scenario, the end-treatment of

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pollutants(EOP) scenario and the coupling measures (CM) scenario have been set to describe future policy

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measures related to the development of the pulp and paper industry in 2010-2020. The outcome of this study

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indicates that the energy saving amount under the CT scenario is the largest, while under the SA scenario

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smallest. Under the CT scenario, savings by 2020 include 70 kt/year of chemical oxygen demand (COD)

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emission reductions and savings of 7443 kt of standard coal, 539.7 ton/year ammonia nitrogen (NH4-N) emission

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reductions and savings 7444 kt standard coal. Taking emission reductions, energy-savings, and cost-benefit into

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consideration, cleaner technologies like high efficient pulp washing, dry and wet feedstock preparation and

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horizontal continuous cooking, medium and high consistency pulping, and wood dry feedstock preparation are

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recommended.

ACS Paragon Plus Environment

is the


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Key words: Emission reduction; energy saving; cost-benefit; bottom-up model; pulp and paper

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TOC art

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TOC Art

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1. Introduction

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The control of wastewater pollutants and the reduction in energy consumption are both the key objectives of

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environmental management in industry. The Chinese government has been carrying out a series of pollutant

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control and energy-saving policies. In recent years, The 12th Five-Year-Plan about National Economy and

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Social Development1clearly indicated that the emission reduction goal that calls for the total quantity of chemical

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oxygen demand (COD) should be reduced by 8% and the discharge of ammonia nitrogen (NH4-N) should be

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reduced by 10% by 2015 compared with that in 2010. In addition, it has been proposed that the energy

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consumption per unit of GDP should be reduced by 16% in 2015 based on 2010 level, resulting in energy savings

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of 0.67 Gt in coal equivalent from 2011 to 2015. 2 The pollutant-energy nexus of the wastewater treatment and


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energy consumption is an integrated system. On one hand, energy consumption is needed when removing COD

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and NH4-N during wastewater treatment. In addition, supplemental energy is required for the operation of

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machines. A previous study showed that energy consumption to eliminate 1kg COD or NH4-N would decrease

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with the reduction of total pollutants. 3On the other hand, from the perspective of Life cycle assessment (LCA),

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the additional energy consumption would bring about the upstream emission discharge in the other way round.

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Emission reductions and energy consumption connect with each other and restrict each other. It is very clear that

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one can’t be realized or produced without involving the other. Therefore, the coordination control of pollutant

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emission reductions and energy savings is key to avoiding transference among environmental targets and

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therefore realizing an overall environmental improvement goal. In addition, energy saving can bring about lower

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operational costs for wastewater treatment. Therefore, pollutant reduction ，energy saving，and cost benefits are

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intertwined with respective needs, making it hard to figure out the issues associated with each in isolation.

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There are many studies that have aimed at analyzing emission reduction or energy saving with a

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technology-based bottom-up model, particularly focusing on energy consumption, energy efficiency, and

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greenhouse gas (GHG) reduction. Typical examples are Long-range Energy Alternative Planning （LEAP ）

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model applied to predict the reduction effect of chief atmospheric pollutants and GHG4. TIMES (The integrated

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MARKAL-EFOM System), has been used to assess transport energy consumption and CO2 emissions for China

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and the USA.5 Based on the Asian-Pacific Integrated Model (AIM), 6the potential for energy conservation and

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CO2 emissions mitigation is evaluated in China’s iron and steel Sector.7 Up to now, assessing wastewater

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pollutant reductions using a bottom-up model is relatively lacking. One study assessed energy conservation and

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water pollution reduction in China’s synthetic ammonia industry with a bottom-up model, and another study

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analyzed industrial water conservation by industrial water conservation potential analysis(IWCPA). The



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difference between studies which used bottom-up models to assess emissions reductions and energy savings and

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the ones which focus on wastewater pollutant reduction is the establishment of the technology system and the

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optimization goal. The former mainly selected technologies related to carbon emission reduction and energy

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savings, most of which have negative costs because of saving energy. The latter chose technologies relevant to

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wastewater pollutant reduction, most of which have positive cost.

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The pulp and paper industry is one of the highest energy and emission intensive sectors in China. 8According to

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the latest statistics, the total energy consumption is 1.38 tons of coal equivalent per ton of pulp or paper in

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China.9 The wastewater discharge ran up to 3.94 Gt, accounting for 18.6% of the total industrial discharge. The

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discharge of COD has reached 0.952 Mt, taking over 26% in the whole industrial discharge. The emission of

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NH4-N reached 25 kt, occupying 10.2% in the whole industrial discharge. 10 The existing published works in the

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pulp and paper sector are mainly about water pollution issues, energy issues and co-benefit control. The water

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pollution sector included not only recent wastewater treatment methods, 11 but the application of advanced

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oxidation processes,12 and their combination with biological treatment, to effluents and the re-use of

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Waste-Activated Sludge13 in the pulp and paper industry. What the majority of the studies in energy issues have

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in common is the strong focus on energy conservation14, energy cost15and energy efficiency. 16As for the

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co-benefit control studies, GHG emission reduction and energy consumption have been widely discussed in

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different industries.17

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Our previous studies covered the policy assessment for water pollution control in China’s pulp and paper

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industry18 and established a model for technology forecasting to reduce water pollutant emissions in China's Pulp

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Industry 19, focusing on only water pollution problems. This paper is a follow up of our earlier study and fills in


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an important gap in integrating estimates of wastewater pollutant (COD and NH4-N) discharge related to the pulp

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and paper industry, with energy consumption and cost-benefit analysis. This provides new insights to researchers

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and policy makers interested in (1) getting a better understanding of the pollutant-energy nexus in wastewater

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treatment, (2) keeping a balance between environmental targets and cost benefits when promoting cleaner

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technologies, (3) Analyzing a specific industry as a whole system instead of focusing on one environmental

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factor, (4) providing an optimum cleaner technology list under emission reduction, energy saving and cost

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benefit objectives, (5) identifying whether these recommended cleaner technologies discussed in our study are in

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accordance with other research findings.

90 91

2.

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2.1. A bottom-up technology model

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The model of industrial water pollutant control and technology policy (IWPCTP) is made of five sub-modules,

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including system simulation of industrial technology, basic data collection, scenario setting, environment impact

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calculation and technology optimization. (Fig.1) Sub-module 1 describes the matching relationship among

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process, technology and products. Sub-module 2 covers the macroscopic variables that were used for calculation,

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technology list and technology parameters. Sub-module 3 can represent the industrial structure and many

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developing scenarios are based on industrial history data, present situations and future trends. Based on

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Sub-module 1, 2, and 3 (system simulation of industrial technology, basic data collection and scenario setting),

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we can calculate pollutant discharge, emission reduction, energy consumption and cost benefit, realizing the

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structural and technological decomposition under a specified target of emission reduction and transference

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among environment targets. Sub-module 5 can recognize the optimum technology under constrained conditions,

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like energy saving, emission reduction and cost benefit.

Materials and Methods



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105 106

Fig1.The structure of the IWPCTP model

107 108

2.2. Industrial technology simulation system

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When simulating the technology system aiming at certain industry, one should have an overall understanding of

110

the raw material, product, process types, current status of the related technology, the development trend, and the

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recognition of key industrial pollutant prevention technologies. Based on the matching relationship such as

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“Raw material-Process-Technology-Product”, the pollutant production and the characteristics of the discharge

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route, the framework of pollution emission loads simulation in industrial sectors is comprised of raw material,

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process combination, products, pollution prevention technologies, end-of–pipe technologies and pollutant

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emissions (See the Supporting information for more details).

116 117

In China, the raw material, production process, production scale, and products involved in the pulp and paper

118

industry are complex. During the process of system simulation of industrial technology, regarding the “Raw


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material-Process-Technology-Product” as a unit, we can simulate the technology framework in the pulp and

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paper industry in China (See the Supporting information for more details). Meanwhile, through substantial

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literature research, interviews and discussions with experts in corporations and government in the pulp and paper

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field, we chose 14 typical wastewater pollutant prevention technologies during the process of pulp and paper

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production, including wood dry feedstock preparation, modification batch cooking, modification continuous

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cooking, dry and wet feedstock preparation and horizontal continuous cooking, high efficient pulp washing,

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advanced black liquor recovery, closed screening, oxygen delignification before bleaching, elemental chlorine

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free bleaching(ECF), total chlorine free bleaching (TCF), enzymatic deinking, flotation deinking , medium and

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high consistency pulping, white water enclosed recycling and reuse in paper machines. Later, according to every

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kind of pollution prevention technology and end-of-pipe technology which are applicable to the raw material,

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process, scale and products and the popularity situation in the corresponding process combination, we embed the

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pollution reduction technologies in the framework of the pollution emission loads simulation in the industrial

131

sectors so that we can establish an integrated pulp and paper industrial simulation system.

132 133

2.3. Basic data collection

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The model of basic data is mainly composed of industrial level parameters and technology parameters. Industrial

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level parameters are made of product output, raw material structure, process structure, and scale structure. The

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technology parameter usually is in correspondence with the industrial technology structure, including production

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process parameters, process technology parameters and end-treatment technology parameters. Industrial level

138

parameters can be obtained from the industrial statistical yearbook. Production process parameters were obtained

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mainly from 《The Handbook of Industrial Pollutant Resource Production and Discharge Factor》. 20 The

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process technology parameters can be gained from various sources, such as 《Advanced Industrial Applicable



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Technology Directory》《Feasible Pollution Control Technology Guide》21extensive literature search, field

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surveys, and consultation with experts in this field. For the end-treatment technology parameters, one can utilize

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《The Handbook of Industrial Pollutant Resource Production and Discharge Factor》，《Water Pollution

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Discharge Standard》，《Wastewater Treatment Project Technology Criterion》20as references and conduct some

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more in-depth literature research. We assume that the performance of the technology parameters is stable during

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the process of operation among different enterprises.

147 148

According to the 12th Five-Year-Plan for the development of the paper-making industry, the average annual

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growth rate of output and demand regarding paper and paper board is set as 4.6% during 2011-2015 and 4.2%

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during 2016-2020.Total pulp demand is calculated through multiplying by the pulp to paper ratio of 0.92. The

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ratio of wood pulp demand, recycled pulp demand and non-wood pulp demand is 22%, 62.7%, 15.3%

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respectively in 2010 and 24.3%, 64%, 11.7% in 2015 and 2020. Based on the assumption, total paper and paper

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board output will be 116 Mt in 2015 and 142.6Mt in 2020; the total paper and paper board demand will be

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114.7Mt in 2015 and140.9Mt in 2020; and the corresponding total pulp demand is 104.57Mt in 2015 and

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131.2Mt in 2020.

156 157

2.4. Scenario Design

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In this section, five scenarios are set to describe future policy measures related to the development of pulp and

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paper industry in 2010-2020, including the Business-as-usual scenario (BAU), Structural adjustment scenario

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(SA), Cleaner technology promotion Scenario (CT), End-treatment of pollutants scenario (EOP) and Coupling

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measures scenario (CM) (Table1).The BAU scenario is set assuming no policy intervention and keeps the

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structure and technology the same as in 2010. In the SA scenario, there is phasing out of backward small-sized

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production capacities by changing plant size and scale. 22The requirement is that chemical wood pulp lines below


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51kt/yr, non-wood pulp lines below 34kt/yr and recycled fiber-based pulp lines below 10kt/yr must be closed.1

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Promoting cleaner production technologies in both new and existing plants is shown under the CT scenario. (See

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Table 2 for details). The current popularity rate of the key cleaner technologies in Table 1 are based on literature

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review. Future popularity rates are investigated through technology guidelines and experts’ suggestions.23As for

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the EOP scenario, it is realized by stricter discharge limitations. The proportion of tertiary treatment in large and

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medium enterprises have been increased a lot. Until 2015, the application rate of tertiary treatment will reach

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40% and until 2020, it will reach 80%. 24In the CM scenario, the combined effects of all individual policy

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measures are presented and reach an ideal environmental performance.

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Table1 Outline of pollutant control policy scenarios in the pulp and paper industry Scenario Name Scenario Description

Business-as-usual scenario(BAU)

Keep the industrial external policy environment the same as 2010 and make the development of technology with a low inertial pace.

Structural adjustment scenario

Close down backward small-sized pulp and paper plants, limiting backward energy

(SA)

consumption technologies and increasing the average size of newly built mills.

Cleaner technology promotion

Promote cleaner production technologies in both new and existing plants, reaching

Scenario (CT)

expectation standard of relevant national environmental technology catalogue and technology promotion policy. The change of industrial structure is the same as BAU.

End-treatment of pollutants

Implement stricter discharge standard and fasten the promotion as well as the

scenario (EOP)

transformation of end-treatment technologies. Techniques of wastewater handling and recycling would be enhanced remarkably.

Coupling measures scenario (CM)

Combine different kinds of wastewater pollution prevention technologies, adjust industrial structure and the CT、EOP， achieving the ideal effect.

175 176 177

Table2 Technology popularity rates in the CT scenario(%) Technology

Wood

dry

Popularity rate

feedstock

preparation Modification

batch

cooking Modification continuous

2010

2015

2020

55

75

90

18

28

38

10

25

45



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cooking Dry and wet feedstock preparation

and

horizontal

continuous

40

70

85

45

70

90

30

60

85

30

60

90

50

80

85

15

45

50

cooking High

efficient

pulp

washing Advanced

black

liquor

recovery Closed screening Oxygen

delignification

before bleaching ECF TCF

2

6

10

Enzymatic deinking

2

8

20

Flotation deinking

40

75

90

20

40

65

20

40

65

Medium

and

high

consistency pulping White

water

enclosed

recycling and reuse in paper machines

178 179

2.5. Calculation

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The environmental impact calculation model includes pollutant discharge calculation, energy consumption

181

calculation and cost benefit calculation.

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2.5.1. Pollutant discharge calculation

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On a yearly basis, the total amount of pollutant emissions from the pulp and paper industry are simulated. Firstly,

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the pollutant generation coefficient of each production process is calculated based on the diffusion of cleaner

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technologies, which is shown in Eq. (1)

186

G(tm+∆,it, s ,a ), p = G(tm ,i , s , a ), p ⋅

187 188

Where m refers to the raw material, i refers to production process; s is the production scale; a is the product; ( m , i , s , a ) refers to the combination of the production process; p is the pollutant, ct is the cleaner technology;

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G(tm,i , s , a ), p

t  1 − θ ct,( m ,i , s , a ) ,p ⋅ β ct,t +∆  ( m ,i , s , a )  ∏ct  1 − θ t ct∈SET( m ,i ,s ,a )  ct,( m ,i , s , a ) ,p ⋅ β ct,( m ,i , s , a ) 

(1)

refers to the generation coefficient of pollutant p from the combination of production


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θct,( m,i ,s ,a ) ,p

190

process ( m , i , s , a ) for producing per unit product a within year t;

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while cleaner technology ct is applied to the combination of production process ( m , i , s , a ) meeting the

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prerequisite that

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combination of production process ( m , i , s , a ) within t under the circumstance that

194

the time span and usually is set as 1 year; the set of

195 196

combination of production process ( m , i , s , a ) .

197

To calculate the pollution reductions from the end-of –pipe treatment, the pollutant emission coefficient is

198

therefore derived from Eq. (2)18

199

  t E(tm ,i , s , a ), p = G(tm ,i , s , a ), p ⋅  γ eop ∑ ,( m , i , s , a ) ⋅ (1 − ϕ eop ,( m ,i , s , a ), p )   eop∈SET(eop  m ,i , s ,a )

200

Where eop is called the end-of-pipe technology;

201

the combination of production process ( m , i , s , a ) for producing per unit of product a within year t;

202

the application rate of eop in the combination of production process ( m , i , s , a ) within t;

203

removal ratio of pollutant p through eop applied in the combination of production process ( m , i , s , a ) ;

is the reduction rate of pollutant p

t 0 ≤ θ ct,( m ,i , s , a ) , p ≤ 1 β ct,( m ,i , s , a ) ; is the popularity rate of cleaner technology ct applied in the

0 ≤ β ct,t ( m ,i , s , a ) ≤ 1

;

∆t refers

to

ct

SET( m ,i , s , a )

E(tm ,i , s , a ), p

is the cleaner technology collection applied in the

(2)

refers to the emission coefficient of pollutant

from

t γ eop ,( m,i ,s ,a )

ϕeop,(m,i,s,a), p

is

is the

eop

204

SET( m ,i ,s ,a )

is the collection of eop technology interconnected with the combination of production

205 206

process ( m , i , s , a )

207

In the end, the total emission load is calculated through summing up the emission loads of all production

208

processes as given in Eq. (3)18

209

TE At , p =

.

∑

D (tm , i , s , a ) ⋅ E (tm ,i , s , a ), p

(3)

( m , i , s , a )∈ SET A( m ,i , s , a )

TEAt , p

210

Where A refers to certain industry,

211

of product a through the combination of production process ( m , i , s , a ) within t;

is the total emission load of pollutant p within t;

D(tm ,i , s , a )

is the yield

( m,i ,s ,a )

process ( m , i , s , a )

SETA

is the collection of

212 213

production

214

2.5.2. Energy consumption calculation

215

The reduction of pollution by certain technologies can lead to the consumption of energy. The calculation of

in industry A.



216

energy consumption is shown as Eq.(4)

217

∆ECt tech = ∑ Pt ⋅ PRi ,t ⋅ ECi i

∑ P ⋅ PR t

j,t

⋅ ES j

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(4)

j

218

where i 、j refers to the set of pollution reduction technologies during the production process in a certain industry;

219

P is the product output; PR is the technology popularity rate; EC is the index of energy consumption per unit of

220

product; ES is the energy economic index per unit of product.

221 222

2.5.3.Cost benefit calculation

223

The total investment cost per year is calculated as Eq.(5)

224 TL

225 226 227 228 229 230 231

fC = P ⋅ IN ⋅ PR ⋅

i(1 + i) i ,t TL (1 + i) i ,t − 1

(5)

where f C refers to the total fixed cost; P is the product output in accordance with certain technology; IN is initial investment; i is the discount rate (Based on the national standard, i is set as 8%), T L is the technical life span (20—40 years). The total investment cost within t years can be summed up as Eq.(6) TL  i (1 + i ) i ,t  fCt = Pt ⋅ ∑  IN i ,t ⋅ PRi ,t ⋅  TL (1 + i ) i ,t − 1  i 

(6)

232

Where

233

The smaller the unit cost of pollution reduction, the better the technology of pollution reduction from the

234

perspective of cost benefits, which means that this kind of technology is recommended.

fC t

refers to the total fixed cost within t year.

235 236

3. Results

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3.1. Energy saving trends under policy scenarios

238

The result of the energy saving amount under different policy scenarios is presented in Fig1. The amount of

239

energy saving under CT scenario is the largest as the high popularity of the pollutant reduction technology and

240

the industrial structure keeps the same development model as the BAU scenario. The energy saving amount is


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8.94 Mt and 13.2Mt in coal equivalent in 2015 and 2020 respectively, which is 2.6 times and 3.8 times compared

242

with that in 2010.The energy saving amount of the SA scenario is the smallest as small-sized pulp and paper

243

mills with backward production capacities have been eliminated. However, those kinds of mills usually have

244

high emission discharge and low energy consumption. Therefore, the integrated energy saving effect of SA

245

scenario decreased a lot. As for the CM scenario, it’s the combination of all the individual policies, which

246

emphasize on controlling different measures and therefore reaching better emission reduction effects. The effect

247

of energy saving is not necessarily better than that of BAU. This paper only considered the cleaner technology

248

during the production process and disregards the energy saving amount of end-of-pipe treatment. Thus the

249

energy saving amount of each technology under EOP scenario is the same as BAU scenario.

250 251

In order to understand the extent of contributions from each technology to industrial energy saving, we

252

decomposed the emission reduction technologies during the production process under different kinds of policy

253

scenarios (Fig.2) Even though the amount of energy savings under different industrial scenarios may be different

254

for a particular technology applied, the differences in the amount of energy savings between different

255

technologies applied are relatively consistent across all industrial scenarios. In particular, dry and wet feedstock

256

preparation and horizontal continuous cooking and high efficient pulp washing can save the most energy,

257

accounting for 70%-80% of the total amount of energy savings. Other technologies, including medium and high

258

consistency pulping and wood dry feedstock preparation, can save 20%-30% of the total energy.



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1400

2010year

2015year

2020year

1200

The energy saving amount （10 kt in coal equivalent）

1000 800 600 400 200 0

BAU

SA

CT

EOP

CM

259 260 261 262 263

Fig2.The energy saving amount produced in the application of emission reduction technology under different scenarios. This paper only considered the cleaner technology during the production process and disregards the energy saving amount of end-of-pipe treatment. Thus the energy saving amount of each technology under the EOP scenario is the same as the BAU scenario

264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283

Fig3. Decomposition of the emission reduction technologies under different scenarios

284 285

3.2. The emission reduction cost analysis under CT scenario

286

The cost benefit curve about COD and NH4-N in 2020 is shown in Fig4,5, which is accomplished through


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287

inserting an area chart in Microsoft excel. Based on the calculation of the unit cost of pollution reductions, we

288

can regard the unit cost of pollution reduction of all the technologies on the Y-axis and regard the pollution load

289

of each technology on the X-axis. The width of a bar in the Fig4,5 represents the amount of emission reduction,

290

which means the wider the width is, the larger the emission reduction amount is. From the width of the bar in

291

Fig4,5, we can see TCF, closed screening and advanced black liquor recovery have remarkable effect of reducing

292

both COD and NH4-N. Comparing the cost benefit curve of COD with cost benefit curve of NH4-N, the unit

293

emission reduction cost of NH4-N is much higher that that of COD, which is approximately 400 times that of

294

COD. From the reduction cost per unit COD and reduction cost per unit NH4-N, enzymatic deinking , flotation

295

deinking and oxygen delignification before bleaching have relatively less investment, about 0.04 Yuan/kg COD,

296

61.5 Yuan/kg NH4-N. However, flotation deinking is applicable to the small recycled paper deinking industry,

297

but the ratio of small pulp mills would result in a decreasing trend with the impact of the policy on the

298

elimination of backward production capacity, and therefore the potential of emission reduction will be at a

299

standstill in the future. Modification batch cooking and modification continuous cooking have the highest cost

300

when reducing the emission of COD and NH4-N as the equipment is expensive and the processes are complex.

301

Thus, enzymatic deinking and oxygen delignification before bleaching are recommended based on cost.

302



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3.5 1 The unit emission reduction cost(Yuan/kg COD)

3.0

2 3

2.5

4 5

2.0

6 7

1.5

8 9

1.0

10 11 12

0.5

13 14

0.0 0.E+00

1.E+04

2.E+04

3.E+04

4.E+04

5.E+04

6.E+04

COD emission reduction amount (ton)

303 304 305 306 307 308 309

Fig 4. The COD emission reduction cost benefit curve in 2020 Note:1-Enzymatic deinking,2- Flotation deinking,3- Oxygen delignification before bleaching,4- Closed screening,5-Wood dry feedstock preparation,6- High efficient pulp washing,7- Dry and wet feedstock preparation and horizontal continuous cooking，8-TCF,9-ECF,10- White water enclosed recycling and reuse in paper machines,11- Advanced black liquor recovery，12- Medium and high consistency pulping，13- Modification continuous cooking，14- Modification batch cooking

310 1

The unit emission reduction cost (Yuan/kg NH4-N

1,400

2

1,200 1,000 800

4

312

5 6

313

千克氨氮）

/

7

600

8 9

400

10

314 315

11 单位减排成本（元

200 12 13

0

14

0

100

200

300

400

500

NH4-N emission reduction amount (ton)

319 320 321 322 323

311

3

316 317 318

Fig 5. The NH4-N emission reduction cost benefit curve in 2020 Note:1- Oxygen delignification before bleaching,2- Enzymatic deinking,3- Flotation deinking,4- Wood dry feedstock preparation,5- High efficient pulp washing,6-TCF,7- Closed screening,8-ECF，9- Dry and wet feedstock preparation and horizontal continuous cooking，10- Advanced black liquor recovery， 11- Medium and high consistency pulping，12- Modification continuous cooking，13- Modification batch cooking，14- White water enclosed recycling and reuse in paper machines


Page 17 of 24


324 325

3.3 The integrated analysis of emission reduction, energy saving and cost benefit under the CT scenario

326

The results of the COD & NH4-N emission reduction prevention technology sequence and the relationship

327

between emission reduction and energy saving in 2020 are presented in table3. The lower the cost is, the higher

328

the rank is. Based on cost, we can get the cost priority sequence of pollution emission technology. However,

329

considering that saving energy can bring about economic benefit

330

brought by each technology into economic benefit and take the fixed investment of technology into consideration,

331

the cost priority sequence of pollution emission technology would change a lot. For example, ECF and TCF

332

ranked in the middle based on cost. When considering the economic benefits of energy, the unit pollutant

333

reduction cost of ECF and TCF are the highest as they are energy-intensive technologies.

25

we convert the amount of energy saving

334 335

When adding the yearly emission reduction amount and energy saving amount data brought by the 14 cleaner

336

technologies, they can achieve 70 kt/year COD emission reductions and economize 7443 kt of standard coal,

337

539.7 ton/year of NH4-N emission reductions and economize 7444 kt of standard coal in 2020. If we compare the

338

data of emission reductions and energy savings, we can find that the cleaner technologies can be divided into two

339

categories: The first category is the technologies that can realize the pollutant reductions but increase the energy

340

consumption, including modification continuous cooking, ECF and TCF. The second category are the

341

technologies that can both reduce the COD and NH4-N discharge and have remarkable effect of energy saving,

342

including wood dry feedstock preparation, dry and wet feedstock preparation and horizontal continuous cooking,

343

modification batch cooking, medium and high consistency pulping and high efficient pulp washing.

344 345

Considering the multiple targets synthetically, including the emission reduction, energy saving and cost, the

346

recommended cleaner technologies include high efficient pulp washing, dry and wet feedstock preparation and

347

horizontal continuous cooking, medium and high consistency pulping, wood dry feedstock preparation.



348 349 350

Page 18 of 24

Table3 COD &NH4-N emission reduction prevention technology sequence and the relationship between emission reduction and energy saving in 2020

Technology name

High efficient

Dry and wet feedstock

Modification

Medium and

Wood dry

Closed

Advanced

Flotation

Enzymatic

Oxygen

White water

Modification

pulp washing

preparation and

batch cooking

high

feedstock

screening

black liquor

deinking

deinking

delignification

enclosed recycling

continuous

horizontal continuous

consistency

preparation

cooking

cooking

pulping

recovery

before

and reuse in paper

bleaching

machines

ECF

TCF

Technology Sequence COD

1

2

3

4

5

6

7

8

9

10

11

12

13

14

NH4-N

1

3

4

2

5

6

7

8

10

9

12

11

13

14

COD

6

7

14

12

5

4

11

2

1

3

10

13

9

8

NH4-N

5

9

13

11

4

7

10

3

2

1

14

12

8

6

COD

2000

2000

2000

3000

5000

1000

11000

0

3000

5000

10000

2000

13000

3000

NH4-N

15.2

15.4

10.3

16.2

52.7

73.5

88.4

0

13.2

43.2

44.1

18.7

118

30.9

COD

251.4

206.7

68.4

189.2

73.2

8.1

9.4

0.7

0

0

0

-0.5

-53.4

-8.7

NH4-N

251.4

189.2

206.7

68.4

73.2

8.1

9.4

0.7

0

0

-0.5

0

-53.4

-8.7

based on cost ( converting energy saving into cost benefit)

Technology Sequence based on cost

Yearly emission reduction Potential(ton））

Energy saving amount(10 kt in coal equivalent)


Page 19 of 24


351

4. Discussion

352

Water pollution reduction and energy saving are identified as prominent environmental issues for

353

environmental management as well as industrial development. The pulp and paper industry is a

354

highly energy and emission intensive sector in China. The development plan for paper industry in

355

the 12th Five-Year indicated that in pulp and paper sector, the average energy consumption per ton

356

paper and paperboard should be reduced by 18% in 2015 based on the data in 2010. In addition,

357

the COD discharge amount should be reduced by 10-12% and the discharge of NH4-N should be

358

reduced by 10% in 2015 compared with that in 2010. 1Thus, the issues of wastewater emission

359

reduction and energy savings should be solved simultaneously.

360 361

In this study, development of the IWPCTP model enables us to analyze how cleaner technology

362

and policy would collectively influence the coordination control of wastewater emission

363

reductions and energy savings combined with economic benefit. Policy scenarios are adopted to

364

assess the energy saving trend in 2010 to 2020. Different policy measures would result in the

365

difference in technology popularity and industry structure. Our study showed that the CT scenario

366

can save the most energy as the high popularity of cleaner technologies and the industrial structure

367

keeps the same development model as the BAU scenario. The early study also showed that the

368

utilization of cleaner technologies in the printing industry reduces energy consumption by

369

149,841kwh/year.26

370 371

Energy saving and emission reductions have drawn wide attention internationally. Among

372

co-benefits of energy saving and emission reduction analyses, most researchers focus on GHG



373

emission reduction rather than wastewater emission reduction. For example, one study has

374

estimated and modeled GHG emission and energy consumption in wastewater treatment plants of

375

the pulp and paper industry.27

376 377

In industrial sectors, in order to speed up the popularization of the cleaner technologies, economic

378

benefit is a key factor to guarantee further development. There should be a balance between

379

environmental targets and cost benefits. The previous study regarded scenario as a unit to estimate

380

cost, 18while our study assessed the emission reduction cost based on individual technology, which

381

helped us select technologies with a lower cost. Considering the multiple targets synthetically

382

covering the emission reduction, energy saving and cost, the recommended cleaner technologies

383

that can eliminate both COD and NH4-N would consist of any one or a combination of the

384

following: high efficient pulp washing, dry and wet feedstock preparation, medium and high

385

consistency pulping, and wood dry feedstock preparation. The China paper association28 and

386

Ministry of Environmental protection of the People’s Republic of China 29also point out that wood

387

dry feedstock preparation, medium and high consistency pulping and high efficient pulp washing

388

are technologies that both save energy and reduce emissions.

389 390

In summary, this study showed the relationship between energy saving and wastewater pollution

391

reduction in the pulp and paper industry and they can interact with each other. In addition, we also

392

provide an optimum cleaner technology list considering environmental benefits and cost benefit,

393

which can be regarded as a technology reference for policymakers and managers in industrial

394

sectors.


Page 20 of 24

Page 21 of 24


395 396

Acknowledgements

397

The authors gratefully acknowledge the financial support from the national Natural Science

398

Foundation of China (71103110) and National Science and Technology Major Project for Water

399

Pollution Control and Treatment (2013ZX07504-004).

400 401 402

Supporting Information

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