S. Henry, F. Oliva, P. Giribone, Ansaldo Energia, Italy
Concern for the environment and all issues linked to respect for earth’s ecosystems are of the greatest importance in current debate, both among the public at large as well as in scientific and industrial circles.
In industry, this attention is being transformed into growing support for eco-compatible design techniques, for the certification of systems (like ISO 14001) and products (EPD, Ecolabel), and for methods of environmental analysis that assess the “environmental impact” of products/services supplied. These environmental policies are paid for, particularly in developed world countries, by benefits in terms of both internal and external image, as well as by the possibility of bidding for contracts that specifically require the use of these techniques (increasingly the case).
Finnmeccia’s Ansaldo Energia is constantly striving to improve its environmental performance, not least by optimizing the use of natural resources and raw materials in corporate production processes, guaranteeing respect for ecology and consideration for the environment as an integral part of the general policies and strategy applied by the company to all its activities.
The LCA was defined in 1990 during the Society of Environmental Toxicology and Chemistry Congress (SETAC) in Vermont as “an objective procedure to assess the energy and environmental impact of a process or activity, by identifying the energy and materials used and the waste released into the environment”. The assessment covers the entire life cycle of the process, starting from the extraction and transportation of raw materials.
The European Community recognized the growing interest in these issues, culminating in the publication of the ISO 14040 series, which describes the principles and reference framework for life cycle assessment. The proposed structure of the regulations is divided into four successive phases:
Goal defining and scoping: defining the subject of the study, the scope of the systems being analysed, the reasons for the limits and assumptions, the data-gathering method and so on
Life cycle inventory (LCI): analysing life cycle phases to build a model of the environmental impact of each of them in terms of the raw materials and energy consumed, and the waste and emissions released
Life cycle diagram of a power generation plant.
Life cycle impact assessment (LCIA): linking the consumption and waste/emissions calculated in the second phase to a particular environmental impact (the greenhouse effect or acidification, for example), and therefore transforming the raw data into an objective indicator of environmental risk
Life cycle interpretation: the concluding phase, during which results are analysed to propose improvements to reduce environmental impact, assessed in terms of LCA to verify that they really do reduce the global impact of the system.
How Ansaldo Energia performs LCA
Ansaldo Energia, on a joint basis with the Department of Production Engineering, Thermoenergy and Mathematical Models at Genoa University, has embarked on the LCA analysis of an 800 MW combined cycle power generation plant for turnkey delivery, which means that Ansaldo Energia is responsible for the design, construction and commissioning of the entire plant.
The sample plant selected is a power station comprising two identical 400 MW units, each consisting of a V94.3A gas turbine coupled to an air-cooled generator; a heat recovery steam generator; a steam turbine with its own generator unit, also air-cooled, and step-up transformers; and an air condenser. Each has their own auxiliaries (pumping station, oil casings and so on). An area for shared auxiliaries is located next to the two units, including the gas reduction station, the demineralised water production plant and the control systems.
The contribution of a plant’s life cycle phases to its environmental impact.
Special attention was focused on the plant’s end-of-life period, with the aim of restoring the site to the greenfield conditions present before construction. As much as possible was also done, given the technology available and economic feasibility, to recover as much material as possible for the “secondary” raw material market.
The life cycle of the plant was then broken down into its component phases and for each of them the various groups of inputs (mainly raw materials and energy) and outputs (mainly emissions and waste) that contribute to their environmental impact were identified.
Study of auxiliary phase operation
As the main aim of the study is to assess the typical impact of a plant during auxiliary phases rather than in-service operation, it was decided to exclude the impact associated with generating electric power by burning natural gas from the analysis, primarily because the amount of fuel consumed in the 30-year life cycle considered is greater by several orders of magnitude than that of any other material or consumption in other life cycle phases.
In addition, reducing the impact of combustion means primarily improving machine efficiency, which is already pursued for technical, economic, market and environmental, reasons. Furthermore, in-service operation is already regulated by national and international legislation, requiring that emissions of certain critical gases, such as CO and NOx, be maintained below a set value, and this ensures that exhaust gases are constantly monitored and improved.
Each individual phase in the life cycle has been analyzed in detail using primary data wherever possible, in other words data gathered in the field from engineering offices, internal workshops, the suppliers of the main components and the work site. Given the huge amount of components and materials involved, only the main components in terms of weight and function have been considered (a total of about 22 000 tonnes of material) and the main materials used or consumed at the work site (more than 106 000 tonnes).
Impact of decomissioning phase
Boustead Model v5 software was then used to calculate mental impacts of energy consumption, global warming and acidification, expressed as a percentage of the total.
An analysis of the results obtained from impact assessment reveals that start-up is the life cycle phase with the greatest environmental impact. To understand the reasons for this environmental cost, the various operations in the phases were analyzed individually to discover which makes a high contribution to energy consumption and the greenhouse effect.
At the end of this study it was found that natural gas combustion linked to the start-up of the gas turbine during, for example, the cleaning of the steam generator piping, was the main activity from both points of view, confirming initial considerations that led to in-service combustion being excluded from the study.
The response to this result took the form of a series of internal activities and projects, such as participation in the European Community technology project Zero Emission Fossil Fuel Power Plants.
Analyzing the results
On completion of the LCA analysis on the sample plant, the results obtained were used as the point of departure to “build” a method addressed to calculating the energy and environmental impact of the life cycle of a combined cycle power plant designed and built by Ansaldo Energia.
This method will make it possible to obtain results about the environmental cost of plants much faster than is possible with a full LCA, as long, of course, as the components involved are of the same type and approximately the same size as those in the sample plant.
However, it should be remembered that there are only a few manufacturers in the world capable of producing components for projects of this type, particularly the most important ones, and so the same suppliers are often involved.
The main power station components (turbines, electrical machines, cooling cycle, large transformers, feed pumps, auxiliary components, and so on) are also mainly a function of plant features (output, gas turbine characteristics, closed cycle characteristics, environmental conditions), which can be regarded as standard apart from minimal deviations mainly linked to the geographical location of the plant. However, these translate into variations for components that are negligible in terms of environmental impact.
A sensitivity analysis was performed on each phase in the life cycle based on results obtained using data from various plants, all combined cycles, but with different configurations or layouts. The output of this analysis work, combined with the results of the LCA performed on the sample plant, was processed to create the environmental impact computation method for a power generation plant, which reduces both the time and resources needed to perform an environmental study and significantly simplifies data collection.
This method can be used at two points in a plant’s life cycle: in the bid phase, using forecast data or specially created internal databases to provide customers with another parameter against which to compare different design or operation choices, and then afterwards, using actual data to calculate environmental impact. Internally, the tool will help designers assess different design options. In both cases, the model requires less input than a full LCA.
This information can be found in contracts or estimated/actual data, minimizing the number of resources needed to perform the analysis, at the same time as significantly reducing the time needed to collect data, which is the most critical activity in the performance of a full environmental analysis.
Once the method had been defined, it was validated by applying it to the same plant on which the full study had been performed, in order to compare results and check for any significant differences and their causes. The percentage differences are minimal, less even than 1 per cent in the case of the global impact of the entire life cycle in two of the environmental impacts considered.
The method can therefore be considered valid. The only significant difference is in the transport phase: the causes of this discrepancy are easy to identify, because while in the LCA study the number of haulage journeys was obtained from work site entry slips, the software calculates the number of journeys by dividing the total weight by the capacity of the means of transport used, so obtaining the “ideal” number of journeys needed, which will in fact be much higher.
As obtaining information from the site is both fairly difficult and not immediate, it seems inevitable that we have to accept some uncertainty in the final result generated by this phase, particularly considering that its impact on the overall result is minimal.
The method developed by Ansaldo Energia to calculate the environmental impact associated with the life cycle of a power plant satisfies the need to reduce the time and amount of data needed to complete an environmental analysis compared with a full LCA.
This makes it possible to calculate impact in a timescale that is compatible with the bidding and basic design processes, using either estimated data or extracting the information necessary from constantly updated internal databases, or alternatively actual data for the various phases of the project. This in turn provides customer with a useful tool to present the environmental impact information needed to obtain permits to begin production and in-house designers with useful information for any peer reviews of the project.