Enel has inaugurated a pilot post-combustion CCS plant at its 2640 MW Federico II coal fired power plant in Brindisi in southern Italy, where CO2 will be captured using chemical sorbents and then liquefied and transported to the Eni/Stogit site in Cortemaggiore to be injected underground for permanent storage.

Sauro Pasini, Enel, Italy

The International Energy Agency (IEA) estimates that world demand for primary energy will grow by 36 per cent through 2035, in the New Policies Scenario.

Despite the extensive development of renewable energy resources, fossil fuels are expected to continue to play an important role, with the demand for coal growing by 20 per cent. In fact, coal will remain the primary energy resource, from which 32 per cent of electricity will be generated. According to the IEA, demand for electricity will rise by 80 per cent by 2035, and the world will need 5900 GW of new capacity. All this could translate into an increase in emissions of carbon dioxide (CO2) from 29.3 billion tonnes in 2008 to 35.4 billion in 2035.

The way to ensure that such a scenario has no irreversible impacts on the environment is to invest substantial resources in promoting technological innovation and the take-up of low-carbon technologies in the energy sector, in other industrial sectors and in transportation.

For electricity generation, the main responses are represented by carbon-free power generation, such as renewable sources, and by those technologies that can reduce or eliminate emissions of CO2 emissions from power plants, an approach known as carbon capture and storage (CCS).

According to the IEA, CCS could contribute to reducing CO2 emissions from thermoelectric power plants by up to 3 billion tonnes a year, but the relative immaturity of these technologies will slow their dissemination on a large scale. This is why the European Union and the governments of the major European countries, the United States, China, Australia, South Korea, South Africa and others have pledged to support research, development and application on an industrial scale of this technology.

Grand CCS plans for Enel

Enel wants to be a leader in this technological challenge, as well as in the development of all low-carbon technologies, to ensure a steady supply of environmentally sustainable power at competitive costs.

Enel has long been committed to various projects in the area of CCS. In particular, since 2002 it has carried out programmes to test and demonstrate the three main CO2 capture technologies applicable today: pre-combustion, combustion in oxygen (also known as oxyfuel) and post-combustion.

Post-combustion capture technology is the most mature and appropriate solution for retrofitting existing coal plants. It is installed downstream from the boiler: CO2 is removed from the flue gases of power plants through a process of chemical absorption. The flue gas passes through a packed column and is washed with a sorbent, usually an amine. The CO2 is absorbed by the amine and separated from the flue gas. The sorbent is then heated to release pure CO2 ready to be compressed and stored.

Carbon capture at Federico II coal plant

Enel’s programme for the development of post-combustion capture technology involves a pilot system at the Federico II power plant in Brindisi in the southern Italian province of Puglia, and the subsequent construction of a large-scale demonstration plant at the Porto Tolle plant at Rovigo in the Veneto.

To reach this challenging programme’s target, Enel decided to investigate all the principal aspects of a new capture technology. Setting up a laboratory-scale mini-pilot has enabled the investigation of amines’ reaction rate and degradation and the development of analytical methods to be used both for process control and degradation monitoring.

A large-scale pilot plant, 10 000 Nm3/h in size, has been constructed as a slip-stream of the Brindisi Sud coal fired power plant. The pilot plant separates CO2 from a slip stream of flue gas out of a wet flue gas desulphurization unit (WFGD) to test real operating conditions. The design of the plant has been optimized to test conventional monoethanolamine (MEA) or commercially available sorbents. A joint Enel and Eni agreement was also signed in 2008 to develop and test systems to liquefy, transport and store the CO2 underground.

The technology demonstration will be followed by installing a CCS system on an ultra-supercritical 660 MWe unit at the Porto Tolle power plant. The post-combustion capture equipment will be designed to treat a flue gas corresponding to 250 MWe and to separate approximately 1 megatonne/year of CO2, which will be transported to an offshore saline aquifer.

The Porto Tolle Zero Emission project covers the design, procurement and construction of the CCS demonstration plant. In the framework of the project, all the detailed studies related to CO2 transport and site characterization will be carried out with the aim of verifying the feasibility of the injection and storage of CO2 in a safe and verifiable manner.

The project is co-financed by the European Union’s EEPR (European Energy Programme for Recovery). A contract was awarded in 2009 with a total funding of €100 million ($140 million) covering R&D activity, CCS engineering and geological surveys and injection testing of CO2 in the saline aquifer to July 2014

Brindisi pilot plant raises scale of ccs

The pilot plant in Brindisi is one of the first of its scale in Europe and in the world. It can process 10 000 Nm3/h of flue gas to separate 2.5 tonnes/hour of CO2, achieving up to 8000 tonnes per year, equal to the CO2 absorbed by around 800 000 trees.

The components that comprise Enel’s pilot post-combustion CCS plant in Brindisi

The basic engineering of the plant was completed at the end of 2008, and detailed engineering ended in April 2009. The permitting procedure for the construction of the pilot was concluded in February 2009. The realization of the plant was achieved at the beginning of 2010; the commissioning was carried out between May and September 2010 and the testing activities are ongoing.

The pilot plant is fed with desulphurized flue gas taken before the stack of Unit 4 after the existing WFGD system. To match flue gas purity conditions, needed to avoid excessive solvent degradation or other adverse impact on CO2 capture plant operation, an additional WFGD and a wet electrostatic precipitator (WESP) have been installed on the slip flue gas stream. This pre-treatment enables sulphur dioxide (SO2)and dust concentrations to be controlled before the CO2 absorber inlet.

The WFGD is a standard spray tower scrubber, fed with a 25 per cent wet limestone–water slurry prepared in the power plant FGD system. The WESP is of honeycomb type. To assure saturation industrial water is sprayed at the WESP inlet.

The pre-treatment plant opens up the possibility of partially bypassing both the WFGD and the WESP. This allows Enel to evaluate the effect of different pollutant levels on the operation of the CO2 capture unit. The technology chosen for CO2 capture utilizes a 20–30 per cent (weight based) MEA aqueous solution to wash the flue gas stream.

Commissioning and preliminary tests

The first test campaign with the 20 per cent (weight) MEA solvent was carried out from June to September 2010, with equipment and parametric tests performed to establish the optimum parameters at different flue gas flow rates.

For the performance tests, three different operation conditions were tested:

  • Nominal gas load: 10 000 Nm3/h
  • Maximum gas load: 12 000 Nm3/h
  • Minimum gas load: 3000 Nm3/h

The guaranteed values for the three different plant conditions are shown in Table 1.

Table 1: Guaranteed values for the capture of pollutants under three plant conditions

The plant’s performance was very encouraging. All the guaranteed parameters were respected. To validate the process parameters, mass and heat measurements were performed on the individual elements and on the whole plant. In particular, a comparison between the CO2 flow rate measured with the on line instrumentation and the gas and liquid balance was performed: the difference between the calculated value and the measured value was very low – less than 5 per cent.

To complete the analysis of tghe capture section, the evaluation of the steam consumption for the regeneration was performed. The specific heat consumption – 4.12 gigajoules/tonne of CO2 – was lower than the expected consumption of 4.20–4.50 gigajoules/tonne of CO2. This difference is due to the stripper’s high performance and the excellent recovery of heat in the cross heat exchanger.

The second campaign commenced on 15 November 2010, with a 30 per cent weight MEA solvent, to be used in benchmarking for further tests. Parametric tests were performed to find optimized operating conditions and investigate the influence of different parameters.

During a long-run test operation of 500 hours, emission measurements were taken to detect MEA and some of its degradation products – NH3, TOC, VOC and aldehydes – coming out of the absorber and the stripper. Very good mass balance closure was achieved; the specific heat consumption resulted in about 3.45 gigajoules/tonne of CO2, as seen in Figure 2. The solvent consumption during the period was estimated at 1.5 kg/tonne of CO2. Enel’s CCS R&D activities

Figure 2: Specific heat consumption during a long-run test of 500 hours

The Brindisi pilot plant will be the test rig for assessing solvent performance and gaining experience in operating capture units while investing in the Porto Tolle demonstration project. The main topics of R&D activity over the next two years will be:

  • Assessment of the MEA absorption technology: reliability, environmental impact, power consumption and capture performance;
  • Definition of operating procedures and management;
  • Cost evaluation at different operating conditions for retrofit application: solvent consumption, inhibitors, waste treatment management;
  • CO2 stream composition and emissions.

Further activity will be focused on reducing the energy consumption and the capital costs of carbon capture technology, while also improving on its environmental performance. To work towards this target, the most promising advanced processes will be tested at the Brindisi pilot plant.

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