The environmental impact of cogeneration systems is considered, with a focus on wastes from cogeneration and their allocations to products. The question of how to allocate wastes for an energy system with multiple products such as cogeneration has long provoked much debate and disagreement, in part because proposed methods lack consistency, simplicity, sound reasoning, ease of use, and universal - or at least widespread - acceptability. Various allocation methods for cogeneration wastes are described, including methods based on techno-economic measures such as energy content of products, exergy content of products, economic value of products, incremental fuel consumption to electrical production, incremental fuel consumption to thermal energy production and shared waste savings between electrical and thermal energy, as well as less rigorous waste-allocation methods. The rationale for the methods for allocating cogeneration wastes are detailed, with a particular focus on energy and exergy factors. The advantages of utilizing exergy methods for allocating cogeneration wastes and the balance they provide among cogenerated products are described. The authors in fact propose that exergy methods can form the basis of rational and meaningful allocation methods for wastes that are superior to other such allocation methods. Three detailed case studies are considered. Steam and hot water-based cogeneration systems are considered in the first two case studies. In the third, a comparison is presented of the waste allocations for cogeneration and equivalent independent plants. The material in this chapter is particularly important because, by permitting wastes to be allocated more appropriately among the commodities of cogeneration, its environmental benefits can be better understood and exploited. These benefits should accrue to society through the better design and utilization of cogeneration technologies based on environmental considerations, and through better decision and policy-making by companies and government.

Chapter Contents:

• Overview
• 9.1 Introduction
• 9.1.1 Motivation
• 9.1.2 Outline of chapter
• 9.2 Wastes from cogeneration
• 9.3 Allocation methods for cogeneration wastes
• 9.3.1 Selected methods for allocating cogeneration wastes
• 9.3.1.1 Allocation of wastes based on energy content of products
• 9.3.1.2 Allocation of wastes based on exergy content of products
• 9.3.1.3 Allocation of wastes based on economic value of products
• 9.3.1.4 Allocation of wastes based on incremental fuel consumption to electrical production
• 9.3.1.5 Allocation of wastes based on incremental fuel consumption to thermal energy production
• 9.3.1.6 Allocation of wastes based on shared waste savings between electrical and thermal energy
• 9.3.1.7 Allocation of wastes by agreement
• 9.3.1.8 Allocation of wastes based on other factors
• 9.3.2 Rationale for allocating cogeneration wastes
• 9.3.2.1 Fundamentals of allocating cogeneration wastes
• 9.3.2.2 Energy and exergy factors in allocating cogeneration wastes
• 9.3.2.3 Exergy vs. energy in allocating cogeneration wastes: balance between cogenerated products
• 9.3.2.4 Advantages of exergy methods for allocating cogeneration wastes
• 9.3.3 Further discussion and comparison of allocation methods for cogeneration wastes
• 9.3.4 Section closure
• 9.4 Case study 1: steam-based cogeneration
• 9.4.1 System description
• 9.4.2 Energy and exergy values
• 9.4.3 Waste allocation results
• 9.5 Case study 2: hot water-based cogeneration with district energy
• 9.5.1 System description
• 9.5.2 Energy and exergy values
• 9.5.3 Waste allocation results
• 9.6 Case study 3: comparison of waste allocations for cogeneration and equivalent independent plants
• 9.6.1 Scenario description
• 9.6.2 Energy and exergy values
• 9.6.3 Waste allocation results
• 9.7 Closure

Inspec keywords: energy consumption; waste; cogeneration; environmental factors

Other keywords: environmental impact; products economic value; thermal energy production; products exergy content; cogeneration systems; energy system; electrical production; water-based cogeneration system; incremental fuel consumption

Subjects: Environmental factors; Thermal power stations and plants