Batch scheduling in process industries: an application of resource–constrained project scheduling

The paper deals with batch scheduling problems in process industries where final products arise from several successive chemical or physical transformations of raw materials using multi–purpose equipment. In batch production mode, the total requirements of intermediate and final products are partitioned into batches. The production start of a batch at a given level requires the availability of all input products. We consider the problem of scheduling the production of given batches such that the makespan is minimized. Constraints like minimum and maximum time lags between successive production levels, sequence–dependent facility setup times, finite intermediate storages, production breaks, and time–varying manpower contribute to the complexity of this problem. We propose a new solution approach using models and methods of resource–constrained project scheduling, which (approximately) solves problems of industrial size within a reasonable amount of time. Received: October 15, 1999 / Accepted: March 21, 2000     

Advanced production scheduling for batch plants in process industries

An Advanced Planning System (APS) offers support at all planning levels along the supply chain while observing limited resources. We consider an APS for process industries (e.g. chemical and pharmaceutical industries) consisting of the modules network design (for long–term decisions), supply network planning (for medium–term decisions), and detailed production scheduling (for short–term decisions). For each module, we outline the decision problem, discuss the specifi cs of process industries, and review state–of–the–art solution approaches. For the module detailed production scheduling, a new solution approach is proposed in the case of batch production, which can solve much larger practical problems than the methods known thus far. The new approach decomposes detailed production scheduling for batch production into batching and batch scheduling. The batching problem converts the primary requirements for products into individual batches, where the work load is to be minimized. We formulate the batching problem as a nonlinear mixed–integer program and transform it into a linear mixed–binary program of moderate size, which can be solved by standard software. The batch scheduling problem allocates the batches to scarce resources such as processing units, workers, and intermediate storage facilities, where some regular objective function like the makespan is to be minimized. The batch scheduling problem is modelled as a resource–constrained project scheduling problem, which can be solved by an efficient truncated branch–and–bound algorithm developed recently. The performance of the new solution procedures for batching and batch scheduling is demonstrated by solving several instances of a case study from process industries.     

Multi-item reliability dependent imperfect production inventory optimal control models with dynamic demand under uncertain resource constraint

In this paper, imperfect multi-item production inventory models are considered over a finite time horizon with known dynamic demands. The production rates are functions of time which are taken as control variables. In the production process, reliability plays an important role to improve the quality of products and to decrease the defective rate. The said defective units are partially or fully reworked. The unit production cost is a function of production rate and also dependent on raw material cost, development cost due to reliability and wear-tear cost. There is a constraint on the total production cost termed as budget constraint which is crisp/imprecise/random in nature. The objective of the present investigation is to fix the optimum reliabilities of the production system to have maximum return. Thus, the models are formulated as optimal control problems for the maximisation of profit and solved using Hamiltonian (Pontryagin’s Maximum Principle), fixed-final time and free-final state system, Kuhn–Tucker conditions and Generalised Reduced Gradient Method. Several particular cases are derived from the general model. The models are illustrated numerically and graphically and some managerial decisions are derived.     

罐式煅烧炉后期使用的管理和维护

包铝炭素分厂二车间所采用煅烧设备是八层五组二十室顺流式罐式煅烧炉,其中1#、2#煅烧炉处使用已达10年,超过设计使用寿命进入后期管理使用阶段。在此期间1#炉经历4次烘炉,2#炉经历2次烘炉,使得煅烧炉炉体变形严重,挥发份直接从罐内溢入火道,影响煅烧炉的正常使用。本文主要介绍炭素分厂二车间通过调整工艺参数,改进操作方式,改善煅烧炉使用情况,减缓煅烧炉老化趋势,从而确保煅烧炉的正常运行。     

An investigation of the uncertainty in reproducing the units of pulsed electric and magnetic field strengths in a standard system for producing very-short electromagnetic pulses with a rise time of 20 psec

A method of reproducing the units of pulsed electric and magnetic field strength in a standard system with a pulse rise time of less than 20 psec, constructed using a “cone over a plane” field-generating system is considered. The components of the uncertainty in reproducing the units are analyzed. The extended uncertainty is not greater than 6.5%.     

Capacity assignment of virtual manufacturing cells by applying lot size harmonization

Decentralized manufacturing cells minimize the lead time of products. However, technical and economical restrictions can prohibit the installation of permanent cells. A possibility to overcome these restrictions is 'virtual manufacturing cells'. These cells are defined by production teams who are responsible for the complete process of a group of products. Unlike permanent cells, the layout can be kept in a workshop structure. This results in a double competition between the orders and between production teams for the use of capacities. A new approach to solving this double competition is to limit the occupation time of capacity units. Combined with alternating access to resources by the production teams, this ensures a clearly defined order sequence. A successful way to achieve the limitation of occupation time is the harmonization of lot sizes. This analytical method should be supported by simulation to consider the dynamic behaviour. The authors have developed a simulation reference model to limit the expense of simulation studies for this purpose.     

Coevolution in Commercial Genetic Engineering

This article addresses the problem of selection criteria andmechanisms at work in the production of scientific and technologicalknowledge. The two dichotomies of scientific—technologicalknowledge and public—private returns are used to specifyfour ideal-type environments, which consist of institutionsand incentives and which influence the creation and selectionof new knowledge. The theoretical arguments about knowledgeevolution over time in relation to different selection environmentsand about coevolution of knowledge producers and institutionsare then examined in the case of commercial genetic engineeringfor pharmaceuticals.     

Sustainability of incentives for excellent research — The German case

The state authorities in Germany used to fund public sector research without controlling the performance of the research units. This has changed during past decade, where the dominant mechanism by which formerly unconditional state funds are allocated nowadays is indicator-based performance measurement. The indicator sets used to measure the research-related performance in the German public science sector are usually very narrow, often consisting exclusively of finished doctoral theses and third-party funds. Using a unique dataset of 473 German research units from astrophysics, nanotechnology, economics and biotechnology, this paper outlines principles for the construction of sensible indicator sets for the performance measurement of scientific research groups. It is argued that scientific production is multidimensional. Thus one-sided indicator sets that fail to cover the relevant output dimensions give rise to incentives that will ultimately lower the performance of the science sector in total. Indicator sets should strive for sustainable incentives, which can be guaranteed if the sets are broad enough. As a starting point it is shown that the very common performance indicator ‘acquired third-party funds’ may affect research efficiency negatively, especially if the level of third-party funds is already very high. Therefore, we conclude that third-party funds should be used with great care, if at all.     

Innovation as Collective Action: Conventions, Products and Technologies

This article argues that specific products evidence demand forspecific innovation systems. Economies must therefore supplydifferent innovation systems according to their trade specializationsand output compositions. Products (or product-based subsectors,the equivalent of five-digit SIC sectors) are the basic unitsaround which innovative action can be ‘supplied’.Understanding and promoting innovation requires understandingof both the demand and supply sides. A system of innovationrefers to the interaction of demands, attached to products,and supplies, attached to these organizational structures ofthe economy, as dual sequential processes ‘out of equilibrium’and involving reciprocal selection. The approach used in thispaper reflects the ‘economics of conventions’, anemerging school of economic thought which holds that economiescan be conceived as sets of rules, largely implicit in nature,which actors generate and by which they coordinate themselvesunder conditions of uncertainty. The task of analysis is tounderstand the cognitive and efficiency properties of functioningsytems of conventions, as well as their emergence and transformationover time.     

Engineering the acyltransferase substrate specificity of assembly line polyketide synthases

Polyketide natural products act as a broad range of therapeutics, including antibiotics, immunosuppressants and anti-cancer agents. This therapeutic diversity stems from the structural diversity of these small molecules, many of which are produced in an assembly line manner by modular polyketide synthases. The acyltransferase (AT) domains of these megasynthases are responsible for selection and incorporation of simple monomeric building blocks, and are thus responsible for a large amount of the resulting polyketide structural diversity. The substrate specificity of these domains is often targeted for engineering in the generation of novel, therapeutically active natural products. This review outlines recent developments that can be used in the successful engineering of these domains, including AT sequence and structural data, mechanistic insights and the production of a diverse pool of extender units. It also provides an overview of previous AT domain engineering attempts, and concludes with proposed engineering approaches that take advantage of current knowledge. These approaches may lead to successful production of biologically active ‘unnatural’ natural products.     

Using biomass as an energy source with low CO2 emissions

This work deals with the carbon dioxide cycle and emissions from biomass incineration under a hydrogen production context. It is proposed to use the thermal energy obtained by biomass combustion to produce water steam, which afterwards would be converted into hydrogen by high temperature electrolysis (HTE). In France, the thermal energy potential from nonvalorised biomass reaches almost 6.5 Mtep. In this study, the potential avoided carbon emissions are quantified as well as the feasible hydrogen production capacity based on the steam supplied by the incineration units. Results show that carbon consumption in hydrogen production by steam methane reforming (SMR) or biomass incineration–HTE process is almost equivalent between both processes. However, the hydrogen produced by the biomass incineration–HTE process used to fuel vehicles, would lead to a decrease of 135 Mt of carbon from fossil origins yearly, in contrast to SMR.     

Co-production models with random functionality yields

Production systems with random functionality yields and downward substitutable demand are modeled and investigated. Such systems arise frequently in the electronics and petrochemical industries. We analyze two single-period models. The first models a single production process in which the total yield of usable products is uncertain; furthermore the realized usable products are of two grades, higher and lower, and the portions of each grade products are also uncertain. Demand for lower-grade products can be met, if necessary, by higher-grade units. The second model we analyze has two parallel production processes: one is as in die previous model; the other is attempting to produce lower-grade products only, but their yield is random. In both single-process and two-process scenarios the relative magnitudes of the salvage values of the two product grades lead to somewhat different models that need to be analyzed separately. We prove that all the expected profit functions are concave (jointly concave), and derive me optimality conditions. Some related modeling and managerial issues are discussed.     

Determination of the mechanical losses of electrical rotor machines and the level of degradation

Some aspects of modeling of overtravel that is observed in rotor-type electric machine units are examined. Methods are proposed for determining the physical and engineering parameters of those units. The maximum effect from the results of the work could be obtained by using them to supplement the traditional methods of using products under actual conditions. Deceased. Translated from Izmeritel'naya Tekhnika, No. 4, pp. 55–57, April, 1999.     

Modeling and analysis of the product assignment problem in single stage electronic assembly systems

Consider the production of an evolving family of similar products, each having a well-defined life cycle. The fundamental production resources are inherently flexible, i.e., reconfigurable and reprogrammable. Two distinct strategies can be followed in configuring production facilities: (1) focused facilities, where a facility is dedicated to one product at a time, but may be reassigned; and (2) nonfocused facilities, where setup operations permit a variety of products to be produced during a given planning period. When focused facilities are used, which is a common strategy in some electronics companies, products must be assigned to specific facilities. If facilities are not identical, and capacity is limited, then changing production requirements may force reassignment of products from one facility to another. Thus, the product assignment/reassignment decision may have a significant impact on the production capacity required. This paper concentrates on the product assignment/reassignment decision when a pure focused facility strategy is used. This problem is analyzed and a number of insights are developed. Based on this analysis, the problem is reformulated and an optimal solution procedure based on a multi-commodity network flow model is presented and tested for the product assignment/reassignment decision     

Controllable production rates in a family production context

We consider a single facility dedicated to the production of a family of items where the policy used is to cycle production through the items every T units of time. This is known as the Common Cycle or Rotation Schedule and is a special case of the Economic Lot Scheduling Problem (ELSP). We consider the case in which the production rates can be reduced from known maximum rates. Moreover, we assume that production rates can be changed during the production runs. We optimally partition the items into those with high and low holding costs. The former are initially produced to meet demand while the latter are always produced at their maximum rates. Numerical examples indicate savings almost twice as large as those reported in the literature.     

Campaign planning for multi-stage batch processes in the chemical industry

Inspired by a case study from industry, the production of special chemical products is considered. In this industrial environment, multi-purpose equipment is operated in batch mode to carry out the diverse processing tasks. Often, extensive set-up and cleaning of the equipment are required when production switches between different types of products. Hence, processes are scheduled in campaign mode, i.e. a number of batches of the same type are processed in sequence. The production of chem ical products usually involves various stages with significant cumulative lead times. Typically, these production stages are assigned to different plants. A hierarchical modelling approach is presented which co-ordinates the various plant operations within the entire supply network. In the first stage, the length of the campaigns, their timing, the corresponding material flows, and equipment requirements have to be determined. At this stage, an aggregation scheme based on feasibility constraints is employed in order to reflect the limited availability of the various types of production equipment. The second stage consists of an assignment model, which allocates the available equipment units between the production campaigns determined in the first stage of the solution procedure. In the third stage, resource conflicts are resolved, which may occur if clean-out operations and minimal campaign lengths have to be considered. The proposed hierarchical approach allows a more compact model formulation compared to ot her approaches known from the literature. As a result, a very efficient and flexible solution approach is obtained. In particular, commercially available standard solvers can be used to solve a wide range of campaign planning problems arising in the chemical industry.     

Evaluation of the potential hazard of secondary radioactive contamination of underground water by sewage works

The time dependence of the distribution of the volume activity of radionuclides over ground layers is calculated under chemically equilibrium and hydraulically stationary condition sand under conditions of continuous operation of radioactively hazardous units of sewage works. As initial information, a set of data on the hydrogeological characteristics and physicochemical properties of the sewage-water sediments (SWSs) found at the sewage works of Chechersk and Slavgorod is used. The results of the calculations performed are analyzed, and the data on the egress of radiocesium from the SWSs found in the sludge areas and filtration fields with different bases into underground water are presented. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 3, pp. 557–560, March–April, 2000.     

First passage time control charts assuming power law intensity for time to jointly monitor time and magnitude

Control charts are essential tools to monitor the quality of a process and commonly used in many industries besides industrial production. Due to the industrial revolution, many products have very low failure chances and labeled as the high-quality products, where the time-between-events (TBE) charts are commonly used to monitor such processes. This study purposes control charts to monitor time and magnitude assuming the power law process for the TBE whereas the magnitude is assumed cumulative as well as noncumulative over time. Besides two illustrative examples, a comparison to the existing rate and first passage time (FPT) charts is also presented in this study. It is shown numerically that the proposed charts are more efficient than the existing FPT and rate charts.     

Nonparametric adaptive age replacement with a one-cycle criterion

Age replacement of technical units has received much attention in the reliability literature over the last four decades. Mostly, the failure time distribution for the units is assumed to be known, and minimal costs per unit of time is used as optimality criterion, where renewal reward theory simplifies the mathematics involved but requires the assumption that the same process and replacement strategy continues over a very large (‘infinite’) period of time. Recently, there has been increasing attention to adaptive strategies for age replacement, taking into account the information from the process. Although renewal reward theory can still be used to provide an intuitively and mathematically attractive optimality criterion, it is more logical to use minimal costs per unit of time over a single cycle as optimality criterion for adaptive age replacement. In this paper, we first show that in the classical age replacement setting, with known failure time distribution with increasing hazard rate, the one-cycle criterion leads to earlier replacement than the renewal reward criterion. Thereafter, we present adaptive age replacement with a one-cycle criterion within the nonparametric predictive inferential framework. We study the performance of this approach via simulations, which are also used for comparisons with the use of the renewal reward criterion within the same statistical framework.     

Dimensionless units and numbers

The theory of measurement, scales is used to show that there is no foundation for attempting to extend the SI system to measurements of quantities and properties which are described by ordering and naming scales or by absolute scales. It is proposed that the units of planar and solid angles should be considered to be outside the system. Dimensionless quantities are conditionally classified. An analysis is made of specified order scales in which the concept of a “unit of measurement” is not applicable and for which it makes no sense to attribute dimensionality to the numbers and scale points used in them. Translated from Izmeritel'naya Tekhnika, No. 9, pp. 3–10, September, 1999.