2015 International Conference on Management Science & Engineering (22th) October 19-22, 2015 Dubai, United Arab Emirates Optimal Policies in Remanufacturing System with Product Substitution under the Constraint of Carbon Emissions WEI Li,CHEN Wei-da,LIU Bi-yu School of Economics and Management, Southeast University, Nanjing 211189, P.R.China Abstract: Given increasing concern related to CO2 and other greenhouse gas, green manufacturing is a choice for manufacturers to reduce their carbon emission. This paper studies the decision problem of steel remanufacturing with two kinds of products produced in blast furnace and electrical furnace and a downward substitution under the constraint of carbon cap and trade mechanism. The profit-maximization optimal production model with carbon cap and trade mechanism is established. The condition satisfied by the optimal policy is given. The numerical experiments are shown to illustrate the impact of carbon price, carbon cap on the strategy with product substitution, carbon emission, the total profit and the substitution quantities. Some managerial insights and policy implication regarding the steel remanufacturing enterprise and the government are obtained. Keywords: remanufacturing, product substitution, carbon emission, production decision 1 Introduction Given industrial development and improved living standards, steels play an important role in our modern societies, while steel enterprises are supposed to be a prime source of the carbon emission. From an economic perspective, steel recycling is cheaper than mine virgin ore. The recycling of scrap iron and steel plays will be a trend in supplying precious raw material for steelmaking [1] . Iron and steel recycling has been considered of important to society, almost 75million tons of steel were recycled or exported for recycling in 2008 in the US alone [2]. In china, the consumption of scraps rose from 3.44 million in 2001 to about 8.1 million in 2009, an increase 2.4 fold. Depending on the grade of steel and steelmaking process, internal steel components may be made using either 25 percent or more than 90percent recycled steel [3]. The chemical process industries are a major contributor to greenhouse gas emission, especially carbon dioxide. The iron and steel recycling is also a Supported by the National Natural Science Foundation of China(No.71271054, 70971022), the Scientific Research Innovation Project for College Graduates in Jiangsu Province(No.CXZZ12_0133) 978-1-4673-6513-0/15/$31.00 ©2015 IEEE becoming especially important in the context of environmental benign steelmaking. Many countries have attempted to enact legislation or design market-based carbon trading mechanism for controlling carbon emission since the global warming caused by CO2 and other greenhouse gas (GHG). Due to the production operation of manufacturing enterprise is the main source of carbon emission, manufacturing enterprises are under growing pressure to reduce their carbon emission. The carbon cap and trade mechanism are both economical problem and technical matter and they will become even more significant in the future for the purpose of reducing carbon emission. Laurens G. et al. [4] considered introducing a remanufacturable product in a market that consists of heterogeneous consumers who have different choice to the retreaded tires. The low-end and high-end consumer populations are different across markets. They discussed the impacts of the market and technology drivers of product manufacturability and identified some phenomena of managerial importance. Klausner et al. [5] considered the remanufacturing of electrical motors. Products containing remanufactured electrical motors have no significant differences in quality or can be sold in a low-end market at a discounted price. In order to satisfy the customer’s special demand for the product with different quality and price, a remanufacturer have to produce different quality remanufactured products. In this paper, we investigate the decision problem of steel remanufacturing with returned product remanufacturing and product substitution under the constraint of carbon emissions, where a remanufactured product with high quality level may be used to substitute another one with low quality level. The following literature discussion is intended to provide context for the production planning with carbon cap and carbon emission trading. Letmathe et al. [6] presented two mathematical models that can be used by firms to determine their optimal product mix and production quantities in the presence of several different types of environmental constraints, in addition to typical production constraints. In the research [7], a mixed-integer nonlinear programming (MINLP) model was proposed for the production planning of refinery processes to achieve maximum operational profit while - 219 - reducing CO2 emissions to a given target through the use of different CO2 mitigation options. Hua et al. [8] studied how firms manage carbon footprints in inventory management under the carbon emission trading mechanism. They used an EOQ model to obtain the optimal order quantity, and also analyzed the impacts of carbon trade, carbon price, and carbon cap on order decisions, carbon emissions, and total cost. Bin et al. [9] studied the multi-item production planning problem with carbon cap and trade mechanism and analyzed the impacts of carbon price on the shadow price, production decisions, carbon emission and the total profit. Note that the decision problem of remanufacturing with returned product remanufacturing and product substitution under the constraint of carbon emissions has not been investigated. Gong et al. [10] consider the manufacturer how to make a balance between carbon emission and production policy. Nouira et al. [11] not only cinsider the selection of manufacturing processes, but also input items (components). A optimization models formanufacturing systems considerthe environmental impacts is showed. Wellington et al. [12] study the optimal product mix under emission restriction, propose Interior analysis to solve this problem. Shen et al. [13] analysis the manufacturer’s production decision-making problem under carbon cap and carbon emissions trading. While many works are related to the production planning for remanufacturing, the literature dealing with remanufacturing and products substitution at the same time is limited. The related literature considers the product substitution under various situations. Regarding one-way product substitution, Inderfurth [14] present combines methods to analysis the optimal policies in hybrid manufacturing/remanufacturing systems. Bayındır. et al[15] jointly consider one-way product substitution and a capacity constraint of the manufacturing/remanufacturing system. Rao. et.al [16] study the Multi-product inventory planning with downward substitution, stochastic demand and setup costs and present a two-stage integer stochastic program model. Bayindir et al. [17, 18] investigated the profitability of remanufacturing option. They constructed a single period profit model under substitution to investigate remanufacturing was profitable. Li et al. [19] investigated an uncapacitated muti-product production planning problem with returned product remanufacturing and demand substitution, where no backlog and no disposal are allowed. A dynamic programming approach was derived for the optimal solution. In 2007, they analyzed a version of the capacitated dynamic lot-sizing problem with substitutions and return products and applied a genetic algorithm to determine all periods requiring setups for batch manufacturing and batch remanufacturing[20]. To respond to government regulatory on carbon emission and environment concerns, same researches in operations management (OM) and operations research (OR) have been arisen in the efforts optimizing operational decisions. Huang et.al[21] congsider a multiple-product newsboy problem with partial product substitution, develop an iterativealgorithm to solve the model. Liu et.al[22] study the two-way productsubstitution and present an ewsvendor game with the impact of loss aversion. Ahiska et.al[23] also study a product substitution strategy for a stochastic manufacturing/remanufacturing system and formulat it as a discrete-time Markov Decision Process. Zhang et.al[24] concentrate on the consumer environmental awareness and channel coordination with two substitutable products within a one-manufacturer and one-retailer supply chain. Most studies on product substitution focused on the impact of substitutable, overlooked the factor of natural environment (Carbon emissions etc.)The objective of the study was to focus on the green manufacturing and develop an optimization model, to achieve the optimal expect profit, by integrating the carbon emission scheme. Integrating the carbon emission scheme in steel remanufacturing makes it possible to choose their remanufacturing technology to comply with the regulations. We optimize production planning with carbon cap and trade mechanism. A mathematical model is presented to formulate the problem. We derive the optimal solution of production and carbon trading quantities. In practice, steel can be subdivided into different categories which represent different chemical composition standards. People are pursuing different grade steel products for diverse purposes in the market, when the demand of one product is not satisfied, the product substitution can avoid the loss coursing by the stock out. And the same time, the steel remanufacturing firms face the challenge of managing product production system with product substitution under the constraint of carbon emission. To reduce CO2 emission, the industry is undertaking long-range, high risk research and development into new steelmaking processes whose designs emit much less CO2. This is the main problem we are going to study in this paper. Zhang et.al[25] use an empirical analysis to verify the relationship of CO2 reduction and Chinese iron & steel (IS) companies. Tang et.al [26] recognize the energy consumption cost as a nonlinear function of the production quantity in a steel production process, a mixed integer nonlinear programming(MINLP) model is formulated. Tang [27]also investigates the effective decisions for the batching problems of steelmakingand continuous-casting production. [28,29] study the continuous casting planning. In order to improve the efficiency and feasibility of charge planning, Dong et.al[30] formulated a multi-objective mathematical programming model and designe Two new meta-heuristics. These papers focus on the on the production control of a complex industrial process which is set in the steel-making process and has been almost no consideration for the possible influence of carbon emission. Considering the iron & steel (IS) companies are traditional high-emission industries, to take same action must be necessary. In this paper, we solve the joint carbon emission and product subsititution problem faced by an iron & steel (IS) companies. - 220 - The rest of the study is organized as follows. Section 2 describes the problem and gives a mathematical formulation. In section 3, numerical experiments are provided to illustrate the impact of carbon price and carbon cap on production decisions, carbon emission and the total profit. In the last section the findings of the study are summarized. τ i : Per unite capacity When the demand for remanufactured products demand is not fulfilled, a substitution takes place. The steel products with low quality can be substituted by steel products with high quality. This results in the following substitution quantity q : if x1 − D1 ≥ D2 − x2 > 0 D2 − x2 (1) q= x1 − D1 2 The problem and mathematical model if D2 − x2 > x1 − D1 > 0 The expected amount of substitution is denoted by In this paper, we consider optimal policies of a steel remanufacturing enterprise which produce two kinds of steel products using the recycled steel and iron products as raw material,called product 1 and product 2. There are two main steel production processes: blast furnace plants and electrical furnaces. The blast furnace plants are considered as integrated plants, while the electrical furnace plants are called semi-integrated plants. But the electrical furnace steel making is far less energy intensive by comparison with the blast furnace steel making from both resources use and CO2 emissions perspective. The product 1 is produced in integrated plants, which is of high quality. In semi-integrated plants, iron scrap is put directly into electrical furnace to produce steel products, called product 2. The steel remanufactured products with different quality have been undistinguishable in terms of functionalities. The two kinds of steel remanufactured products satisfy different types of consumers at different prices. When the demand for products with high-level quality (product 1) is fulfilled, the producer can offer a product (product 2) with high-level quality instead a product with low-level quality in case of a shortage of a product with low-level quality. We will focus on a single-period problem with independent stochastic demands for both product types. The following notations are used throughout the paper. i : product index xi : production quantities Di : random demand for product i q : quantity of product substitution fi ( x) : probability density function of the demand for product i Fi ( x) : probability distribution function of the demand for product i demand Fi −1 ( x) : inverse distribution function of the demand forproduct i : Selling price per unit product i pi si : Salvage value per unit product i ci : Production cost per unit product i ce : Carbon price per unit ei : Carbon emission per unit product Eg : Carbon cap Q( x1 , x2 , D1 , D2 )= E[min[max( D2 -x2 ,0), max( x1 D1 ,0)]]] x1 x1 + x2 -D1 0 x2 = ∫ f1 ( D1 ) ∫ x1 ∞ 0 x1 +x2 - D1 + ∫ f1 ( D1 ) ∫ ( D2 - x2 ) f 2 ( D2 )dD2 dD1 (2) ( x1 - D1 ) f 2 ( D2 )dD2 dD1 In this problem, for maximizing the total expected profit, the steel remanufacturer has to decide the optimal production quantities and the corresponding carbon trading quantity L . And the total carbon emission will 2 be ∑ ei xi , in the optimal carbon trading quantity L it i =1 2 xi holds the following relation ∑ ei = i =1 Eg + L [12]. If L > 0 , the manufacturer buys emission permits form the carbon trading market; otherwise, he sells its unused permits − L . The carbon trading quantity L = 0 means the steel manufacture will not involve in the carbon trading. Now, we are ready to present the optimization model with product substitution under the constraint of carbon cap. Max = p ( xi , L) E[ p1 min( x1 , D1 ) + s1 ( x1 − D2 ) + ] + E[ p2 min( x2 , D2 ) + s2 ( x2 − D2 ) + ] + ( p2 − s1 ) Q( x1 , x2 , D1 , D2 ) − x1c1 − x2 c2 − ce L (3) subject to 2 x ∑e = i =1 i i 2 ∑τ x i =1 i i Eg + L (4) (5) ≤σ (6) The objective function (3) maximizes the total expected profit for both products. In models, we + max(⋅,0) . For guaranteeing a profitable let (⋅)= remanufacturing business, we assume the cost value of product 1 is greater than product 2, that is c1 > c2 . And, we also assume that p1 > p2 > c1 > c2 , p2 > c2 > s2 and c1 > s1 > s2 . To avoid the general case, the steel remanufacturer get more revenue from selling product 1 than product 2 and the positive profit can obtained in the situation that using product 1 to satisfy the demand of product 2, that is p1 − c1 > p2 − c2 > p2 − c1 > 0 . It is reasonable in practice because the products with high quality have a higher performance than products with low quality. From Eq. (4), we have xi ≥ 0 (i = 1, 2) 2 ∑e x − E : the carbon trading quantity σ : the total capacity L i =1 i i g = L. (7) Substituting Eq. (7) into Eq. (3), this also means the - 221 - following. ( p2 − c2 − ce e2 ) − ( p2 − s2 ) F2 ( x2 ) − ( p2 − s1 ) Max= p ( xi , Em ) E[ p1 min( x1 , D1 ) + s1 ( x1 − D1 ) ] + E[ p2 min( x2 , D2 ) + s2 ( x2 − D2 ) ] + + ∫ + ( p2 − s1 ) Q( x1 , x2 , D1 , D2 ) − x1c1 − x2c2 − ce (∑ ei xi − Eg ) 2 ∑µ x 0 x2 −( p2 − s2 ) ∫ F2 ( D2 )dD2 i =1 0 x1 + x2 − D1 x2 x1 ∞ 0 x1 + x2 − D1 + ∫ f1 ( D1 ) ∫ (8) Proposition 1. The expected profit function is jointly concave in xi , i = 1, 2 . x1 F1 ( x1 ) = ∂p = ( p1 − c1 − ce e1 ) − ( p1 − s1 ) F1 ( x1 ) + ( p2 − s1 ) ∂x1 0 ( p1 − c1 − ce e1 ) + λτ 1 + µ1 +( p2 − s1 ) ∫0 f1 ( D1 )(1 − F2 ( x1 + x2 − D1 ))dD1 p1 − s1 p1 − s1 (14) f1 ( D1 ) F2 ( x1 + x2 − D1 )dD1 x1 ∂p = ( p2 − c2 − ce e2 ) − ( p2 − s2 ) F2 ( x2 ) − ( p2 − s1 ) ∂x2 , x1 (13) λ ∗ be the optimal shadow price. Then the x1∗ , x2∗ can be derived from the first-order optimality condition.From equation (9) and (10), we can derive the optimal values of each of the decision variables which are satisfied the following equations: Proof. First,since ∫ (12) =0 Let x1∗ , x2∗ be the optimal production decision, and ( x1 − D1 ) f 2 ( D2 )dD2 dD1 ] i =1 x1 i i λ represents the shadow price of the common capacity. 2 0 (11) λ≥0 ( D2 − x2 ) f 2 ( D2 )dD2 dD1 − x1c1 − x2 c2 − ce (∑ ei xi − Eg ) ∫ (10) f 2 ( D2 )dD2 dD1 + λτ 2 + µ 2 = 0 i =1 =p1 x1 − ( p1 − s1 ) ∫ F1 ( D1 )dD1 + p2 x2 x1 x1 + x2 − D1 0 2 x1 0 f1 ( D1 ) ∫ λ (σ − ∑τ i xi ) = 0 i =1 +( p2 − s1 )[ ∫ f1 ( D1 ) ∫ x1 0 2 F2 ( x2 ) = We have ( p2 − c2 − ce e2 ) + λτ 2 + µ2 +( p2 − s1 ) ∫0 f1 ( D1 )( F2 ( x1 + x2 − D1 ) − F2 ( x2 ))dD1 p2 − s2 p2 − s2 (15) f1 ( D1 )( F2 ( x1 + x2 − D1 ) − F2 ( x2 ))dD1 − x1 ∂ 2p = −( p1 − s1 ) f1 ( x1 ) − ( p2 − s1 )[ ∫ f1 ( D1 ) f 2 ( x1 + x2 − D1 )dD1 + f1 ( x1 ) F2 ( x2 )] 2 0 ∂x1 3 Numerical experiments x1 In this section, we analyze the effect of the carbon price and carbon cap on the strategy with product substitution, carbon emission and the total profit of the steel remanufacturing system with product substitution presented in section 2. For this purpose, we design the parameters sets for illustrating our main results and observe the behavior of the steel remanufacturing system. Demands of the product 1 and 2 are assumed as uniformly distributed, i.e., Di ∈ (ai , bi ), i = 1, 2 , where bi > ai , ai > 0, i = 1, 2 . We set carbon quota Eg = 800 , the = −[( p1 − s1 ) f1 ( x1 ) + ( p2 − s1 )[ f1 ( x1 ) F2 ( x2 ) + ∫ f1 ( D1 ) f 2 ( x1 + x2 − D1 )dD1 ]] 0 x1 ∂p = −( p2 − s2 ) f 2 ( x2 ) + ( p2 − s1 ) ∫ f1 ( D1 )(( f 2 ( x1 + x2 − D1 ) − f 2 ( x2 ))dD1 0 ∂x22 2 = − [( s1 − s2 ) F1 ( x1 ) f 2 ( x2 ) + ( p2 − s2 ) f 2 ( x2 ) x1 [1 − F2 ( x2 )] + ( p2 − s1 ) ∫ f1 ( D1 ) f 2 ( x1 + x2 − D1 )dD1 ] 0 x1 ∂ 2p = −( p2 − s1 ) ∫ f1 ( D1 ) f 2 ( x1 + x2 − D1 )dD1 0 ∂x1 x2 using for abbreviation x1 G ( x1 , x2 ) = ( p2 − s1 ) ∫ f1 ( D1 ) f 2 ( x1 + x2 − D1 )dD1 0 we thus find P: = common capacity σ = 500 , and ce = 1 . The problem parameters are listed in tab.1. ∂ 2ππππ ∂2 ∂2 ∂2 − ∂x12 ∂x22 ∂x1∂x2 ∂x2 ∂x1 = [(p1 − s1 )f1 (x1 )+( p2 − s1 ) f1 (x1 )F2 (x2 )+G ][(s1 − s2 )F1 (x1 )f 2 (x2 ) Tab.1 Parameters of the problem product ai τi ci si bi pi +(p2 − s2 )f 2 ( x2 )[1 − F2 ( x2 )]] + [(p1 − s1 )f1 (x1 )+( p2 − s1 ) f1 (x1 )F2 (x2 )] [(s1 − s2 )F1 (x1 )f 2 (x2 )+(p2 − s2 )f 2 ( x2 )[1 − F2 ( x2 )] + G ] due to p1 > p2 , s1 > s2 , p2 > s2 and ∂ 2π ≤0 ∂x12 , ∂ 2π ≤0 ∂x22 and D ≥ 0 . Namely the Hessian matrix of the objective function is negative semi-definite. Since π is concave, the Karush-Kuhn-Tucker (KKT) condition can be necessary and usefully for the optimal solutions. Let λ , µi , i = 1, 2 be the dual variables corresponding to the constraint (5) and (6). Then, the optimal policies to this problem are xi , i = 1, 2 , if and only if there exists non-negative dual variable λ , µi , i = 1, 2 . Hereby we can have ( p1 − c1 − ce e1 ) − ( p1 − s1 ) F1 ( x1 ) + ( p2 − s1 ) ∫ x1 0 f1 ( D1 ) ∫ ∞ x1 + x2 − D1 1 2 p2 > s1 , It is obvious that f 2 ( D2 )dD2 dD1 + λτ 1 + µ1 = 0 (9) 95 55 45 25 15 10 100 150 0 0 3 2 ei 7 2 In order to figure out the effect of the carbon price on the system, we conduct experiments with varying value of the carbon price, and keep other parameters unchanged. Below is the impacts of carbon cap and carbon price on the shadow price of the capacity, production decisions, carbon emission and total profit. Fig.1 shows that the curves of optimal decisions of steel remanufacturer, we can see that with the carbon price increasing, the quantity of product 1 x1 is decreases, meanwhile the quantity of product 2 x2 is increasing with the carbon price increases until 12.52. After that the carbon price increases to 12.52, - 222 - until ce increases to 12.52. After that, the total carbon emission keeps constant. From this curve, the carbon emission of the remanufacturer is decreases under the situation of carbon emission strategy. It means that carbon price is an effective factor to controlling the carbon emission. When the carbon price increases, the steel remanufacturing firms will choose electrical furnace to produce more economical products which areless carbon inefficient. So, the government can take carbon trade as an effective measure to make firms reduce carbon emission. Fig.1 The curves of optimal production quantities Remanufacturer Fig.3 The curves of the expected profit for different carbon caps Fig.2 The curve of the total carbon of steel emission x1 and x2 keep constant. Because of as the carbon price increases, production 2 will be more economical and low carbon emission. It indicates the steel remanufacturer intend to choose electrical furnace as the main steel making process to avoid high cost and high carbon emission. If the carbon price is increasing, steel remanufacturer will produce more low carbon emission productions. When carbon price is low, to produce production 1 takes the advantage at the low cost. But with the increasing of the carbon price, the remanufacturer will tend to manufacture the product with low carbon emission. Given the production capacity, the decision variables and expected profit will have nothing to do with ce > 12.52 . Fig. 2 shows the total carbon emission. It shows that the total carbon emission decreases with the carbon price - 223 - Fig.4 The expect profit of combination of the carbon cap and carbon price adjust carbon cap properly to prevent fluctuation of the carbon price. 4 Conclusions Fig.5 The curve of the substitution quantities Fig.3 illustrates the impact of the carbon cap and carbon price on expected profit. In order to investigate how the carbon cap and carbon price effect the expected profit, Fig.3 plots the curves of expected costs against carbon price when= Eg 0,= Eg 500,= Eg 1500 respectively. When Eg = 0 , the expected profit decreases as the carbon price increases. When Eg = 500 , the curve have the same shape. They decreases with the carbon price in the case. When Eg = 1500 , the top curve indicates that the expected profit is increasing first and then decreasing with the carbon price. When Eg = 0 and Eg = 500 , the steel remanufacturing firm has to buy carbon permits from the carbon trade market. So the cost of steel remanufacturing increases with carbon price. As a result, the increase of the carbon price will reduce the firm’s expect profit. When Eg = 1500 , the steel remanufacturing firm has extra carbon permits, so the profit increases with carbon price until the profit reach the peak, and then decreases with carbon price. Fig. 4 shows the expect profit of combinations of the carbon cap and the carbon price. The 3-D object in Fig.5 increases as the carbon price and carbon cap increase. Fig.5 illustrates the change of the expect substitution quantities with respect to the carbon price for sets of data as given in the table. The curve shows that Q decreases with the carbon price. The products with low carbon emission will be economical than product with high carbon emission when carbon price increases, thus x1 decreases and x2 increases. The expect substitution quantities is only related to the carbon price and is no sensitive to the carbon cap. There is a significant finding we can get from the analyses. The optimal quantities and the expect substitution quantities are more sensitive to the carbon price, while maximum expected profit is insensitive to the carbon price and the carbon cap. It makes sense to As the growing attention on carbon emission, manufacturers have started to integrate carbon emission concern into their operation decision. In this paper, we study the decision problem of remanufacturing with substitution with the carbon emission constraint that carbon cap and trade. A profit-maximization model is established. By analyzing the decision process and optimal model, we get the equations which optimal solutions satisfied. There are some significant findings by analyzing the impact of carbon cap and carbon price on production decision, carbon emission and total expect profit. Under the carbon emission constraint, with the carbon price increases, the remanufacturer is prefer to produce low-carbon production. At the same time, the total carbon emission decreases. So the carbon cap and trade mechanism can be an effective measure to reduce carbon emission. If remanufacturer have surplus carbon quota, with the carbon price increases, the expect profit will increases. Otherwise, if remanufacturer have not enough carbon quota, with the carbon price increases, the expect profit will decreases. According to the expect profit of combinations of carbon cap and carbon price, the policy makers can design efficient car cap and trade mechanism to balance the remanufacturer’ profit and the total carbon emission. In this paper, there remains several questions which give motivation for future research. At first, we can extend the single-period and address the general multi-period problem case. In each period, the carbon price may be different. Another extension is that we only consider two kinds of carbon constraint: carbon cap and carbon trade, it is very significant to study the remanufacturer production optimal under the other carbon constraint or the combination of carbon constraints. References [1]M Yellishetty, G M Mudd, P G Ranjith, A. 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