Energy & Lifecycle Analysis Flashcards
Sustainable
Technology VS Society VS Environment
There is a finite resource base of environmental sources
The environment has the capacity to absorb the products of our activities provided that these cycles are not perturbed significantly
How to be sustainable
For a renewable resource (soil, water, forest, fish), the rate of usage cannot exceed the capacity of the environment to replenish that resource.
For a pollutant, the sustainable rate of emission cannot be greater than rate at which the environment can recycle or render harmless the pollutant.
For a non-renewable resource, fossil fuels etc.. the rate of usage should not exceed the rate at which sustainable alternatives substituted for it.
UK
In 2012, almost nothing was produced using renewables
Coal was moved away from largely due to circumstance as many of the factories were close to closing down
There has been a steady increase in wind power but there is a reliance on gas (baseload) and nuclear as well
A lot of the gas usage is for heating
Life Cycle Analysis
Life cycle analysis is a systematic way of analysing the impact of an activity or of producing a product.
Considers all phases of the lifecycle of the product or service (cradle to grave).
Very useful for comparing the impacts of different activities so that a rational choice can be made. We must compare like for like, e.g two ways of producing the same good or service.
As engineers we are not in the business of managing the environment. LCA is simply a tool for quantifying the impact(s). The cost-benefit argument for different options can be informed by the LCA, but will ultimately depend on a degree of judgement
Stages
Define goal and scope of the study
Define the functions of the product system
Define the functional unit
Define the boundaries and product system
Set out the methodology, assumptions and limitations
Life-cycle inventory analysis
The quantification of inputs and outputs from a given product system throughout its life-cycle.
Life-cycle Impact Assessment
Assigning the environmental impacts of the product system
Lifecycle interpretation
Use the findings of the inventory and impact assessment to draw conclusions
Defining the Product System
function = the service or product delivered to the user.
functional unit = “Quantified performance of a product system for use as a reference unit in a lifecycle-assessment”
Elementary flow (INPUT) = a flow of material from the environment, which has not been transformed by human means
Elementary flow (OUTPUT) = a flow which is discarded into the environment without further transformation
The system boundary should be arranged so that the material entering or leaving the system is an elementary flow
Inventory Analysis
The inventory analysis involves adding up all the inputs and outputs of the process.
Effectively this will involve detailed mass and energy balances over the product system and will result in an inventory table (i.e. a list of all resources used and emissions to the environment).
The inputs and outputs are divided into data categories
Detailed lifecycle analysis can include many data categories, with the emissions characterised down to individual chemicals.
Impact Assessment
In the impact assessment estimates are made of how much each input and emission contributes to a recognised set of environmental impacts. This is usually done by identifying a set of nine general environmental themes
The contribution of an emission to each theme is expressed by a potency factor.
Site-specific assessment is not practicable in LCA, with processes all over the world often being part of the total system under analysis. For some environmental consequences, this makes sense, e.g. Global warming: Spatial differentiation is not necessary for global problems such as global warming. The atmosphere is well mixed.
abiotic depletion, energy, global warming, ozone depletion, aquatic/terrestrial, acidification potential, human toxicity, photochemical oxidant creation, nutrification
Life Cycle Interpretation
The total environmental impacts of the whole life cycle will have been estimated in terms of the environmental themes, giving an eco-profile.
There can be no basis for assessing the relative importance of, say, ecotoxicity and global warming. Despite this, there have been attempts to quantify the environmental impact in terms of single number, by weighting the various impacts
It is hard to meet our energy demand using renewable resources, such as biomass
We have to worry about the energy we put in to generate energy products. This applies to all forms of renewable energy.
Use too much energy
How to lie with an LCA: Allocation
Avoid allocation (or equivalently use substitution) – see later
Use physical relationships if possible. E.g. vary the amounts of Product 1 and 2 and measure how much the burden changes. If the system is non-linear, then you can use a marginal allocation to compare two states, e.g. how much extra burden is there if one extra unit of product 1 is made?. This is not always possible, e.g. the proportions of soya bean oil and soya meal are fixed by nature.
Simply proportion the burden by some property of the product (e.g. Cost, Mass or Energy content).
Allocation by substitution: Allocation by substitution gives a credit equal to the environmental burden saved by displacing some other product in the market (equal to the burden associated with displaced product)
