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Hazardous waste incinerators (HWIs) differ substantially from thermal power facilities, since instead of maximizing energy production with the minimum amount of fuel, they aim at maximizing throughput. Variations in quantity or composition of received waste loads may significantly diminish HWI throughput (the decisive profit factor), from its nominal design value. A novel formulation of combustion balance is presented, based on linear operators, which isolates the wastefeed vector from the invariant combustion stoichiometry kernel. Explicit expressions for the throughput are obtained, in terms of incinerator temperature, fluegas heat recuperation ratio and design parameters, for an arbitrary number of wastes, based on fundamental principles (mass and enthalpy balances). The impact of waste variations, of recuperation ratio and of furnace temperature is explicitly determined. It is shown that in the presence of waste uncertainty, the throughput may be a decreasing or increasing function of incinerator temperature and recuperation ratio, depending on the sign of a dimensionless parameter related only to the uncertain wastes. The dimensionless parameter is proposed as a sharp a' priori waste 'fingerprint', determining the necessary increase or decrease of manipulated variables (recuperation ratio, excess air, auxiliary fuel feed rate, auxiliary air flow) in order to balance the HWI and maximize throughput under uncertainty in received wastes. A 10-step procedure is proposed for direct application subject to process capacity constraints. The results may be useful for efficient HWI operation and for preparing hazardous waste blends. © 2013 Elsevier Ltd.

Tsiliyannis C.A.,Anion Environmental Ltd.
Renewable and Sustainable Energy Reviews | Year: 2015

Variations in quantities and composition of received wastes in waste to enegy (WTE) plants lead to throughput and power losses (lower profits). By disturbing the mean residence time of flue gases in the air-pollution-control-system they result in temperature and offgas flow variations affecting combustion efficiency and actual pollutant emissions. Besides energy savings, integration by flue gas heat recovery (FHR) in a heat exchanger (recuperator) enables maintaing high throughput under feedstock uncertainty (e.g. poor wastes). An effective method for reducing WTE atmospheric pollution, mainly NOx emissions, flue-gas-recirculation (FGR) - mass recirculation of a fraction of flue gases to the combustor - may be used for the same purpose. Both FHR and FGR are related to robustness issues, limiting the actual range and effect of manipulation. Recent results indicate that FHR and FGR have opposite effects on WTE performance - increasing FGR cools down the combustor, while FHR boosts up combustion. The present work demonstrates the possibility of improving operability of WTE facilities by combined use of FHR and FGR, utilizing multiple waste mixtures with uncertain feedrates, heating value, or composition. It brings forth a key dimensionless parameter, determining the direction and magnitude of the manipulation and leads to explicit expressions for the sensitivities of power production, throughput and capacity constraints with respect to FGR and FHR ratios. Synergistic use of FHR and FGR enables maximization of throughput and power production within the process capacity constraints, without detrimental effects on destruction efficiency or final emissions. A Case Study is analyzed for a facility under a public-private-partnership contract, with received waste ranging from a guaranteed minimum 150.000-200.000 TPY and composition range: biodegradables 52-70% ww, recyclables (paper, plastics, metals, glass) 25-45% ww. © 2015 Elsevier Ltd. All rights reserved.

Tsiliyannis C.A.,ANION Environmental Ltd
Journal of Cleaner Production | Year: 2016

Cyclic manufacturing (CM) emerges as a sine-qua-non for sustainability. Consumer product stocks of today are the end-of-life flows (EoLF) of tomorrow in circular economy. Enacted legislation fosters reuse/recycle of EoL consumer products, of chemicals, raw materials and hazardous products and components (batteries, brake fluids, printed circuit boards, cellular phones, computers). But when is tomorrow and how much of the stock will appear as EoLF? Efficient CM operations depend on cognizance of EoLF and accumulating stock, the pool from which EoLF emanates. Consumer uncertainty, personal income, economic cycles, advent of technology, social and health reasons, stricter eco-standards and random early product losses during use, render EoLF and product stock uncertain and unobservable. Conventional identification methods based on regression, sequential least squares, or actuary science methods presuming specific residual life distributions, may not provide reliable estimates under uncertainty and non-stationarities. An appealingly simple constitutive law is revealed, relating the mean stock and EoLF in terms of stock mean-age and EoLF mean-age, which are scaled, readily and reliably monitored variables, even from relatively small, decentralized samples. Valid under random lifetime early losses, the law encompasses any EoL exit distribution, enabling stock and EoLF identification, data consolidation and assessment. Being a linear algebraic expression between stock and EoLF, the law reduces computational burden and evades presumption of any survival or exit probability distribution, or cognizance of early loss history, or ex-post fitting of stochastic parameters. The results may prove useful in planning/sizing EoL facilities and recycling operations and in environmental policy or compliance assessment. © 2016 Elsevier Ltd.

Due to thermal, or exhaust air blower capacity limitations in cement manufacturing processes, the use of alternative fuels may necessitate production volume reductions from the nominal value achieved by fossil fuels, leading to considerable profit reductions. A novel linear algebraic model is presented herein, which isolates combustion stoichiometry invariants from fuel feed flowrates (decision variables). It allows rigorous, though explicit modeling of the integrated kiln-soil mill-fuel mill system, based on fundamental mass and energy balances. It enables assessment of the impact of key operational parameters and inner circuits on production level and kiln emissions, when alternative fuels (AFs) are used. Necessary conditions for balancing the integrated kiln - soil mill - fuel mill process are given in terms of a priori known physicochemical parameters and process operational data, both for compound and direct operation. A five-step procedure for process balancing is proposed in order to reap the potential benefits of AF use by selecting a non-inferior AF and conventional fuel mixture. It is shown and demonstrated by an actual case-study, that the enthalpy balance is the clinker production level limiting factor (binding constraint) while the kiln - soil mill offgas exhaust blower may be operated well below capacity. © 2012 Elsevier Ltd. All rights reserved.

Tsiliyannis C.A.,ANION Environmental Ltd.
Environmental Science and Technology | Year: 2013

Variations in waste quantities and composition affect incinerator operating conditions and performance. Fluegas volumes consititute a dominant environmental and financial consideration for efficient waste incinerator (WI) operation, since they affect the temperature, throughput, air pollution control system (APCS) residence time, and pollutant emissions, when the charging rate or composition of any waste is varying. Fluegas recirculation (FGR) in WI is an effective technique for reducing WI atmospheric pollution, mainly NOx emissions, albeit affecting WI throughput, temperature and destruction/removal efficiency. FGR refers to mass recirculation of a possibly cooled fraction of fluegases and differs substantially from fluegas heat recovery. The present work shows that, besides emission control, suitable manipulation of FGR enhances WI performance under waste uncertainty, enabling higher throughput, at the desired temperature and within the allowed APCS residence time range. A dimensionless parameter related to the uncertain wastes' net enthalpy contribution is isolated, which encompasses heat of reaction and enthalpy outflows from fluegas and solids and which reveals whether throughput is decreasing or increasing with temperature and FGR ratio. Normalized throughput and total fluegas volume isotherms manifest the interdependence and enable manipulation for enhanced environmental and economic performance. © 2013 American Chemical Society.

Use of alternative fuels (AF) in cement manufacturing is rising worldwide due to environmental benefits and associated subsidies, e.g. CO2 tradeable rights. Ιncreased kiln fluegas volumes from AFs imply lower clinker production, lower residence times in the air-pollution–control-system and removal efficiencies and elevated offgas pollutant emissions. Ever-present variations in AF composition, particularly if refuse derived, intensify operational uncertainty. A rigorous method is presented for quantifying the benefits of oxygen enrichment (OXE) in cement manufacturing, based on fundamental principles (mass and enthalpy balances). It employs a novel multidimensional formulation enabling simultaneous consideration of any number and types of AFs, isolating the invariant part of combustion stoichiometry from the OXE-dependent part and from the uncertain AF composition and flowrates. It was shown that OXE implies higher clinker production and lower fluegas and offgas volumes, while emissions are not impaired or even ameliorate, e.g. NOx emissions. Explicit formulae for clinker and offgas rates are presented, encompassing inner circuiting, direct or compound operation, fluegas bypass and heat integration of clinker cooler with secondary/tertiary air. The potency of the method and the significant benefits of OXE in cement manufacturing are demonstrated in a case study of an actual dry process clinker facility. © 2016 Elsevier Ltd

Tsiliyannis C.A.,ANION Environmental Ltd.
Resources, Conservation and Recycling | Year: 2015

Resource preservation (RP) and homeostasis is a key aspect of sustainability and a prime target of policy considerations. Heralded as an efficient means towards sustainable production and consumption of manmade products, cyclic manufacturing (CM) is fundamentally different from traditional open loop manufacturing: raw materials are not merely resources extracted from the natural environment, but products returned by the consumer as well. RP via CM strongly depends on the quantity and quality of returns. Affected by several factors (economic cycles, income, technological innovation, energy efficiency, social trends, etc.), the majority of returns, including end-of-life (EoL) returns, are random and unobservable. The present work reveals the intricacies of RP under real market conditions, including uncertainty in growth, stock and returns. It is shown that the recycling rate, the reuse rate and key parameters, including mean lifetime, number of reuse cycles and cyclic frequency, may not discern RP enhancement. A simple dimensionless rate is proposed and shown suitable for RP assessment. Its efficacy is demonstrated under leveled consumption/sales, growth or contraction: the minimal rate for reduced virgin material demand is higher under rising sales/consumption and lower in periods of economic austerity. The results may be useful for RP monitoring and proactive sustainable policy. © 2015 Elsevier B.V.

Tsiliyannis C.A.,ANION Environmental Ltd.
Waste Management | Year: 2011

Explicit expressions for the end-of-life flows (EOL) of single and multiple cycle products (MCPs) are presented, including deterministic and stochastic EOL exit. The expressions are given in terms of the physical parameters (maximum lifetime, T, annual cycling frequency, f, number of cycles, N, and early discard or usage loss). EOL flows are also obtained for hi-tech products, which are rapidly renewed and thus may not attain steady state (e.g. electronic products, passenger cars). A ten-step recursive procedure for obtaining the dynamic EOL flow evolution is proposed. Applications of the EOL expressions and the ten-step procedure are given for electric household appliances, industrial machinery, tyres, vehicles and buildings, both for deterministic and stochastic EOL exit, (normal, Weibull and uniform exit distributions). The effect of the physical parameters and the stochastic characteristics on the EOL flow is investigated in the examples: it is shown that the EOL flow profile is determined primarily by the early discard dynamics; it also depends strongly on longevity and cycling frequency: higher lifetime or early discard/loss imply lower dynamic and steady state EOL flows. The stochastic exit shapes the overall EOL dynamic profile: Under symmetric EOL exit distribution, as the variance of the distribution increases (uniform to normal to deterministic) the initial EOL flow rise becomes steeper but the steady state or maximum EOL flow level is lower. The steepest EOL flow profile, featuring the highest steady state or maximum level, as well, corresponds to skew, earlier shifted EOL exit (e.g. Weibull). Since the EOL flow of returned products consists the sink of the reuse/remanufacturing cycle (sink to recycle) the results may be used in closed loop product lifecycle management operations for scheduling and sizing reverse manufacturing and for planning recycle logistics. Decoupling and quantification of both the full age EOL and of the early discard flows is useful, the latter being the target of enacted legislation aiming at increasing reuse. © 2011 Elsevier Ltd.

Tsiliyannis C.A.,ANION Environmental Ltd.
Waste Management | Year: 2012

Dynamic annual flow models incorporating consumer discard and usage loss and featuring deterministic and stochastic end-of-cycle (EOC) return by the consumer are developed for reused or remanufactured products (multiple cycle products, MCPs), including fast and slow cycling, short and long-lived products. It is shown that internal flows (reuse and overall consumption) increase proportionally to the dimensionless internal cycle factor (ICF) which is related to environmental impact reduction factors. The combined reuse/recycle (or cycle) rate is shown capable for shortcut, albeit effective, monitoring of environmental performance in terms of waste production, virgin material extraction and manufacturing impacts of all MCPs, a task, which physical variables (lifetime, cycling frequency, mean or total number of return trips) and conventional rates, via which environmental policy has been officially implemented (e.g. recycling rate) cannot accomplish. The cycle rate is shown to be an increasing (hyperbolic) function of ICF. The impact of the stochastic EOC return characteristics on total reuse and consumption flows, as well as on eco-performance, is assessed: symmetric EOC return has a small, positive effect on performance compared to deterministic, while early shifted EOC return is more beneficial. In order to be efficient, environmental policy should set higher minimum reuse targets for higher trippage MCPs. The results may serve for monitoring, flow accounting and comparative eco-assessment of MCPs. They may be useful in identifying reachable and efficient reuse/recycle targets for consumer products and in planning return via appropriate labelling and digital coding for enhancing environmental performance, while satisfying consumer demand. © 2011 Elsevier Ltd.

Tsiliyannis C.A.,ANION Environmental Ltd.
Waste Management | Year: 2014

Planning of end-of-life (EoL) product take-back systems and sizing of dismantling and recycling centers, entails the EoL flow (EoLF) that originates from the product dynamic stock (DS). Several uncertain factors (economic, technological, health, social and environmental) render both the EoLF and the remaining stock uncertain. Early losses of products during use due to biodegradation, wear and uncertain factors such as withdrawals and exports of used, may diminish the stock and the EoLF. Life expectancy prediction methods are static, ignoring early losses and inapt under dynamic conditions. Existing dynamic methods, either consider a single uncertain factor (e.g. GDP) approximately or heuristically modelled and ignore other factors that may become dominant, or assume cognizance of DS and of the center axis of the EoL exit distribution that are unknown for most products. As a result, reliable dynamic EoLF prediction for both durables and consumer end-products is still challenging. The present work develops an identification method for estimating the early loss and DS and predicting the dynamic EoLF, based on available input data (production. +. net imports) and on sampled measurements of the stock mean-age and the EoLF mean-age. The mean ages are scaled quantities, slowly varying, even under dynamic conditions and can be reliably determined, even from small size and/or frequent samples. The method identifies the early loss sequence, as well as the center axis and spread of the EoL exit distribution, which are subsequently used to determine the DS and EoLF profiles, enabling consistent and reliable predictions. © 2014 Elsevier Ltd.

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