Design for the Environment/Power Generation



Ontario Power Generation (OPG) is one of the largest power generators in North America. The Crown Corporation is owned by the Government of Ontario and it was established in 1999 under the provincial premier, Mike Harris. OPG currently owns 75 power generation facilities across Ontario to generate electricity at a capacity of 22000 MW. It generated over 105 terawatts-hrs (TWh) of electricity in 2006 to supply Ontario’s needs. Nuclear power generation accounts for 44% of the total power generation mix, hydroelectricity for 32%, and 24% for fossil fuel. One of OPG’s primary focuses is to generate electricity in an environmental friendly approach by reducing CO2 and other Green House Gas (GHG) emissions.

Background


The Nanticoke power plant located in Haldimand County, Ontario is the largest coal fuelled power plant owned by OPG. Currently, Nanticoke is using Pulverized Coal (PC) power generation process to generate electricity. The power plant has a total of eight steam turbines which generate electricity at a maximum capacity of 3920MW.

The use of coal to generate electricity produces Green House Gas(GHG) emissions to the environment hence, a retrofit proposal is provided to improve the current electricity generating method at the Nanticoke power plant. The Integrated Gasification Combined Cycle (IGCC) is a well developed technology known to generate electricity using less coal compared to the PC method. Additionally, with the Carbon Capture and Storage (CCS) technology implemented to the IGCC process it reduces the CO2 emission which aids in decreasing the GHG's released into the atmosphere.

Project Information
Section 1 Group 7A Chiu Yuen Huen (THuen) Michael Khelawan (Michael Khelawan) Kiri Panchalingam (Kiri) Geerthanan Thiviyarajah (thiviya1)

Highlights / Recommendations
The Pulverized Coal (PC) power generation method is a traditional method of generating electricity which has inherent negative impacts on the environmental. PC plants are relatively cheap and easy to construct; however, there are increasing demands to reduce GHG emissions. Therefore, the PC generation method, which generates 5100000 MtCO2e of GWP per year, will need to make some changes to reduce emmissions. To replace this old technology, the Integrated Gasification Combined Cycle (IGCC) or IGCC with Carbon Sequestration (CCS) are two promising technologies capable of delivering cleaner energy. CCS is a costly technology at the present day to construct. Nonetheless, the benefits of this technology over-ride the negative aspects and this method can greatly reduce GHG emissions by 90%. Furthermore, considering it can yield oil production for Canadian oil fields by 100% this alternative is best suited as a retrofit to the existing Nanticoke Power Generation Station.

Pulverized Coal
Using coal to produce electricity was initially developed in the 1880’s; however, using pulverized coal (PC) was introduced later in the 1920’s. The success of this technology (at least from an economic sense) is evident from its wide use even today. For example, according to, in 2001, 51% of the electricity generated in the United States was from coal burning plants. The popularity of using PC in power generation stems from the fact that coal “is the most abundant fossil fuel in the world”. However, it would be insufficient to determine the success of this technology solely on economics.

In the United States, roughly 30% of all solid residue from coal combustion is recycled ; a relatively low percentage. At the Nanticoke plant, the ash residue is recycled and sold for use for making cement. However, it should be noted that flue gas desulphurization (FGD) technology has not been used. This technology essentially reduces the amount of sulphur dioxide emitted, by over 90%. In fact, it is evident that the Nanticoke station is a heavy polluter.

The monetary cost of a process is a key factor in determining its relative success. The direct costs associated with the operation of a plant such as the Nanticoke generating station is summarized below:

The above values are from the International Coal Development Institute (ICDI) for typical coal powered power plants. However, since the size of power plants varies significantly, some of the assumptions made by ICDI may not be accurate for the case of the Nanticoke power plant. The above capital costs are calculated at $900/kW of capacity. Therefore using this estimate for the Nanticoke plant, the capital costs would be 3.5 billion dollars (1986 US $); a significant difference. Indirect costs associated with the amount of pollution caused to the environment by the plant also have monetary value. These damages have been quantified by in terms of $/ton for various gaseous releases. The table below shows the costs for the major gaseous releases at the Nanticoke power plant.

If we compare the values from the above two tables, it is evident that the indirect cost is roughly half the direct cost; a substantial amount. Summing the direct and indirect costs, we get a total of 686.4 million dollars. Since many assumptions were made in the process of determining these costs, the numbers are likely skewed. For example, the cost per ton of gaseous releases stated by had a broad range and it was assumed to be the mean of these values.

Integrated Gasification Combined Cycle


Integrated Gasification Combined Cycle (IGCC) is a fast growing technology in the power generation industry. IGCC is being used to eliminate the oxides of nitrogen, sulfur, and greenhouse gas emissions to improve fuel efficiency of the pulverized coal system. This technology generates power with little use of solid and liquid fuel.

The IGCC power plant burns coal to generate electricity but additionally, it uses a gasification method. The added gasification process allows the coal elements to be differentiated from the synthetic gas, which is often referred to as syngas. Syngas is a mixture of carbon monoxide and hydrogen. Followed by the production of syngas, gasses such as hydrogen sulfide, particulate matter (PM) and many other pollutants are removed from the syngas through the use of filters. The cleaned syngas is then combusted in a gas turbine which produces electricity. The steam from this process drives a steam turbine and generates electricity. The process of generating electricity in an IGCC power plant can be seen below.

There are many advantages in choosing an IGCC system to generate electricity rather then the common Pulverized Coal system. One of the advantage that an IGCC system brings forth is its ability to produce electricity through a combination of gas and steam turbine. Additionally, this clean coal technology is an air pollution control, and an environmentally friendly approach. It also achieves ~50% thermal efficiency, which means less coal is needed to produce the same amount of energy as the coal-based system. Nonetheless, with the combination of the new technology such as, Carbon Capture Sequestration (CCS) emissions can be further reduced as explained in CCS section.

The IGCC power plant is a cleaner technology for the environment; however, the economic analysis must also be conducted in order to see the overall benefit of the technology. There are many costs that are taken into consideration in the analysis such as capital, operation and maintenance cost. Refer to Cost Tables for details. However, an IGCC plant cannot be retrofitted to an existing pulverized coal plant therefore it must be built from scratch. Though, many parts can be used from the pulverized coal plant, there are some extra fitting that must be taken into consideration such as the gasifier, syngas cooler and the air separator. Refer to Cost Tables for details. The additional cost that is involved in generating electricity through the IGCC is the disposal of residue cost. The plant requires about 1.1 metric tonne of coal to generate electricity for a year with 44 rails transporting the coal to the power plant. The cost of low sulphur coal as of today is approximately $55 million and the cost of transportation is ~$9.20 million [34]. On average an IGCC power plant uses about 1.1 metric tonne of coal an year which produce roughly 245,000 mt of coal ash. However, only about 85,000 tonne is the fly ash. The disposal of the fly ash is ~$30 a tonne hence, an IGCC power plant can expect to spend about $2.55 million a year for disposal fees.

Many indirect costs should be also considered in a full economic analysis as it reveals the weakness of the power plant. The IGCC power plants’ main source in generating electricity is coal, as mentioned before, it releases many gases into the atmosphere causing premature deaths and long-term health risks. Under the Canada’s Kyoto agreement, the cost of greenhouse gas (GHG) is ~$15/tonne. On average, health damages range from a minimum of ~0.4 billion yearly. The generation of electricity not only cause health issues but, also causes environmental damages. It is evident from the studies that in general, the environmental damages range from a minimum of ~$48 million. It should be noted that the cost of damages does not include all damages and therefore the figures mentioned above should be interpreted with care.

Integrated Gasification Combined Cycle with Carbon Sequestration
Carbon sequestration can be defined as the capture and storage of carbon that would otherwise be emitted into the atmosphere. The process is otherwise known as carbon capture and storage (CCS) and the purpose of this process is to enable the use of fossil fuels while reducing the emissions of carbon dioxide into the atmosphere therefore alleviating global warming which has become a major source of environmental concern.

When carbon sequestration is applied to an IGCC power plant, it is capable of reducing atmospheric emissions drastically by 80-90%. The process would increase the energy needs by about 10-40% and the costs of storage and other system costs are estimated to increase the costs of energy by 30-60%.

There are three types of CCS technologies that currently exist. The method that will be studied is post-combustion, otherwise known as flue gas separation is a process in which CO2 is captured from flue gases. This is currently the best understood method and most commercially used.

The CO2 product can be stored in deep geological formations, deep oceans, or also in the form of mineral carbonates. The most effective way to store sequestered CO2 is the Enhanced Oil Recovery which is the injection of inert gases into depleted oil fields to increase the yield. Therefore, more oil can be extracted from the fields leading to increased energy supply. For this study the captured CO2 will be transported by pipelines from the power plant to the Weyburn Oil Field in Saskatchewan. This field has been chosen for the study because it is currently being used for enhanced oil recovery. The Weyburn Field allows for permanent CO2 storage and over the anticipated 30-year life of the project, it is expected that the injection of 18 million tons of CO2 injected will produce 130 million barrels of oil. This has been calculated to be equivalent to approximately 14 million tons of CO2 being prevented from reaching the atmosphere, including the CO2 emissions from electricity generation that is required for the whole EOR operation. Transporting the CO2 from the Nanticoke plant in Ontario to the Weyburn field will require about 1500 miles of pipelines. In order to make an existing IGCC plant capable of capturing, it needs to be retrofitted with Carbon Capture equipment including 2 CO- Water Gas Shift Reactors, a CO2 Acid Gas Removal Section (AGRU), and a CO2 compressor.

In the resource provisioning stage of the life cycle analysis, the building materials for the plant and the coal that the plant will use for fuel needs to be supplied. The major building materials needed for the plant include concrete and steel. More coal is needed in comparison to an IGCC plant without CCS. It is estimated that 1.35 Mt of coal is used a year, and in a total life-time of 30 years a total of 40.5 Mt of coal is used. To mine this coal it will cost $67.5 million/year and $2025 million/life-time. It is also estimated that it will cost $20.3 million/year or $609 million/life-time to transport this coal to the plant via railway. The retrofits which are implemented to facilitate carbon capture include 2 CO Water Gas Shift Reactors, a CO2 Acid Gas Removal Units and a CO2 Compressor costing $34, $98 and $40 million respectively. The capital cost is $2600/KW and therefore for a 500MW plant $1300 million.

The cost of electricity for IGCC with capture and Enhanced Oil Recovery is 4-8¢/kWh. For this study the cost of electricity at 6.74¢/kWh will be used. In general, there is a 1-2¢/kWh increase in price for IGCC plant to adopt carbon capture technology. For a 500MW plant, the cost of electricity is $29.5 million/year and $885 million/life time of 30 years .The Operating and Maintenance cost is about $31.2/year or for entire life it is $936 million. If carbon dioxide will be transferred via pipeline onshore from the Nanticoke Power Generation center is southern Ontario to Weyburn oil field in Saskatchewan, which is approximately 1500 miles, it is calculated to cost approximately $25/t CO2.

Indirect costs include environmental, health, and social costs. The major environmental benefit of the Carbon Capture and Storage system is that it decreases atmospheric emissions of carbon dioxide by 90%. This will play a major role in alleviating global warming in the future. If carbon sequestration is made commercially available worldwide, and if governments work together to enforce policies for decreased emissions, this global warming crisis can be averted. This technology can not only be retrofitted to power plants, but all industrial and commercial sites emitting carbon dioxide. This technology will help Ontario become a leader in power generation and it will play a major role in Canada’s plans to meet its Kyoto protocol commitment as Ontario still heavily relies on fossil fuels.