Electricity partitioning in chlorine production - Inference Group

Eco-profiles of the
European Plastics Industry
METHODOLOGY
A report by I Boustead for PlasticsEurope Last revision
March 2005 PlasticsEurope may be contacted at Ave E van Nieuwenhuyse 4
Box 3
B-1160 Brussels Telephone: 32-2-672-8259
Fax: 32-2-675-3935
CONTENTS
ECOPROFILE METHODOLOGY 6
OVERVIEW 6
IMPACTS AND INVENTORIES 8
INDUSTRIAL SYSTEMS 9
ECO-PROFILES AND LIFE CYCLES 11
SYSTEMS AND SUB-SYSTEMS 12
INDUSTRIAL NETWORKS 13
MODELLING USING NET FLOWS 15
THE NATURE OF EXTENDED SYSTEMS 16
FUELS 18
THE FUEL PRODUCING INDUSTRIES 19 Oil fuels 19
Coal 20
Electricity 22
Sulphur 26
Combined heat and power plants (CHP) 27 DESCRIBING THE PERFORMANCE OF A SYSTEM 30
ECO-PROFILE CALCULATIONS 32
CALCULATING AVERAGES 32
FEEDSTOCK ENERGY 36
CAPITAL EQUIPMENT 39
HUMANS 39
ECO-PROFILE DATA 40 Data gathering 40
Data quality 41
Complexity of plant 41
Accuracy of data 42
Format of records 42
Sharing common facilities 42
Missing data 43
Common problems 43 INTERCHANGE OF HYDROCARBON FUELS 45
CO-PRODUCT ALLOCATION 46 Establishing system function 46
Simple mass partitioning 47
Using process detail 49
Stoichiometric partitioning 50
Partitioning with excess of reactants 51
Procedure 1 52
Procedure 2 52
Procedure 3 53
Procedure 4 53
Procedure 5 53
Summary 54
Electricity partitioning in chlorine production 54
Simple mass partition 54
Elemental mass partition 55
Partition to NaOH and chlorine only 55
Elemental partition to NaOH and chlorine only 56
Mass partition with allowance for hydrogen 56
Elemental partition with allowance for hydrogen 56
Mechanistic approach (mercury cell) 57
Mechanistic approach (diaphragm/membrane cell) 58
Modified mechanistic approach for the diaphragm cell 59
Partition using reaction enthalpy 59
One stage enthalpy partition 63
Partition using gross calorific value of hydrogen 65
Partition using net calorific value of hydrogen 66
Summary of partitioning methods for the chlorine cell. 66
Using multiple partitioning parameters 66
Substitution partitioning 67
Economic partitioning 68
Partitioning in polystyrene production 69 UNWANTED CO-PRODUCTS 70 Treat the co-product as waste 71
Use a substitution procedure 71
Allocate only materials 72 SULPHURIC ACID DILUTION 73
STEAM CO-PRODUCT 75
STEAM CONDENSATE 76
REPORTING RESULTS 76
FORMAT OF RESULTS TABLES 78 Data categories 78
Energy data 80
The simple energy table 80
Primary fuel tables 82
Fuels expressed as mass 83
Water consumption 83
Raw materials inputs 84
Air emission data 85
Carbon dioxide equivalents 86
Water emission data 87
Solid waste 88
The empirical system 88
EU Solid waste categories 90 UNDERSTANDING ECO-PROFILE RESULTS 91 General observations 91
Interpreting energy data 92 USING ECO-PROFILE DATA 99
REFERENCES 102 ECOPROFILE METHODOLOGY
The purpose of this report is to explain the background and general
methodology that has been used in the eco-profile calculations. It also
explains, in outline, how to make use of the results. Much of the content
of this report is applicable to systems other than polymer production but
there are some unique features of the petrochemical industry that need to
be highlighted.
OVERVIEW
Manufacturing industry is concerned with processing materials and the laws
of science govern the operations involved in this processing. Two
consequences follow from this. First, energy is needed to effect the
desired transformations and secondly, waste is inevitably produced. The
notion that it is possible to produce an energy-free and waste-free
industrial process is a myth. As a result, the best that can be achieved is
minimising the use of energy and reducing waste production. The first step in attempting to achieve this is to describe the situation
that currently exists because this is the base line against which any
future improvements will be judged. Within individual factories, this has been the task of engineers for over a
century because energy use and waste generation directly affect the
profitability of an enterprise. However, the last thirty years have seen
the development of a further stimulus in the form of environmental
pressures from both governments and public opinion. The source of this interest can be traced to the late 1960's when a number
of world modelling exercises were carried out. In particular, the
publication of the National Academy of Science's Resources and man,[?]
Meadows' book The limits to growth[?] and the Club of Rome's document A
blueprint for survival[?] led to considerable concern about the continued
viability of society as a whole. The primary cause was thought to be
increasing population and the inability of the planet to cope with the
consequent demands that would be placed upon it. In particular, all of
these publications singled out the exhaustion of fossil fuels and some of
the scarcer mineral resources, as well as possible pollution problems. With hindsight, some of the predictions of these modelling exercises were
somewhat extreme. Nevertheless they sparked an interest in describing the
behaviour of extended industrial systems. Initially interest focused on the use of energy, especially fossil fuels,
and the work was often referred to as energy analysis. Because the
calculations required the construction of balanced flow charts to describe
the processes, the consumption of raw materials and the generation of solid
waste were also automatically calculated. As a result, some analysts
referred to the work as resource analysis or resource and environmental
profile analysis. One of the earliest reports of the results of this type of work was
presented to the World Energy Conference by Harold Smith from ICI in 1969
and concerned some aspects of the chemical industry.[?] This was followed
in the early 1970's by the publication of a large number of reports on
various production systems[?] and the work was given added impetus by the
oil crises of the mid 1970's. As a result many companies elected to have
their practices examined and reports and publications have continued right
up to the present day[?] although many of these reports have remained
confidential to the sponsoring organisation and are not freely available. During this same period, the environmental lobby was persistent in its
attacks on the packaging industry and especially beverage packaging, where
the introduction of one-trip packs was seen as wasteful. In the USA
pressure grew to promote returnable containers and resulted in the
pioneering legislation in Oregon[?] that has subsequently been repeated
elsewhere. In Europe, the EC Directive on beverage packaging[?] was passed
in 1985. The data needed to implement these different forms of legislation
were all based on the results of energy and resource analysis as a means of
decision making, although it has to be admitted that, at times, the
analyses have not been entirely objective. It is, however, important to remember that long before the interest in
energy occurred, there was awareness, in many parts of the world, of the
localised pollution problems being caused by other human activities.
Litter, the smogs of Los Angeles and Tokyo and acid rain in Scandinavia all
pointed to the need for international action to curb the problems. Then in
the 1980's the potential threat of greenhouse warming and ozone depletion
added to the need to consider the emission of pollutants both to air and
water. (It is worth noting that, like today, pollution control measures are
controversial. Burning coal was prohibited in London in 1273 but it was not
until the Clean Air Act of 1956 that the prohibition became reality!) The methodology for evaluating the global release of these pollutants is
identical to that for calculating energy consumption and so energy analysis
expanded to encompass their computation. As a result, the term energy
analysis fell into disuse and the terms eco-balance, eco-profile, cradle to
grave analysis, life cycle analysis and life cycle assessment appeared, all
essentially describing the same type of work. In the present work, the term
eco-profile has been used rather than life-cycle analysis because the
systems examined follow the production sequence only to the point where the
polymer resin is ready for sale to the converter. The use and final
disposal are not considered and so the results do not represent a complete
life cycle analysis.
IMPACTS AND INVENTORIES
In 1990, the first ever meeting of some of the practitioners in this field
of study met at a conference in Vermont, USA[?]. It was this