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Ymittos Athens, Greece

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. Source

Tsiliyannis C.A.,ANION Environmental Ltd.
Journal of Cleaner Production

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. Source

Tsiliyannis C.A.,ANION Environmental Ltd.
Renewable and Sustainable Energy Reviews

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. Source

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. Source

Economic development and rising consumption increase pressure on the environment. Sustainable production and consumption face the challenge of mitigating impacts under uncertainty in economic growth, trade, raw material availability and prices, variable consumer behavior and technological innovation. Necessary and sufficient conditions and a minimum rate policy for environmental enhancement under uncertainty are presented. They take into account variability in sales/consumption, in net product and material trade and in manufacturing technology and associated impacts. Three main criteria are considered. K1: reduced final wastes. K2: reduced extraction of virgin raw materials. K3: reduced impacts from manufacturing. The conditions are expressed in terms of the cycle rate, which is the generalization of the recycle rate and of readily monitored product flows, e.g. overall sales. Key advantages of the method are discussed. (A): simplicity and flexibility to simulate different growth conditions. (B): a readily determined, standardized rate policy, leading to reduced impacts in K1, K2 and K3. It is quantitatively established that for lower wastes, uncertainty in growth compels increase of the cycle rate larger than a threshold related to sales. For lower virgin material extraction, the threshold includes net product/material trade as well. Reduction of manufacturing impacts requires intensification of cleaner processes with adequately lower marginal impacts. In periods of economic austerity, the policy may be relaxed: enhancement is achieved via lower rate targets. It is concluded that cleaner production becomes all the more important as reuse/recycle flows increase and that such innovation may avert environmental degradation from manufacturing, even under significant growth.© 2014 Elsevier Ltd. All rights reserved. Source

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