PILOT PLANT,CO CAPTURE 2

BRINDISI (ITALY)

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PILOT PLANTCO CAPTURE2BRINDISI (ITALY)Within the general frame of the fight against climate change and with the aim of achieving the zero-emission target, in compliance with the unilateral commitment taken by the EU to reduce, by 2020, at least 20% in greenhouse gas emissions compared with the 1990 levels and with the possibility to increase this target up to 30%, should a global international agreement on climate change be reached, the main electricity producers are presently engaged in the research and development of new technologies to obtain a significant reduction in the CO2 emissions produced by thermal power plants.One of these technologies is represented by the systems grouped under the acronym “CCS” (Carbon Capture Storage). These technologies provide the possibility of capturing the carbon dioxide deriving from combustion processes through a series of chemical processes capable of separating the carbon and making it transportable. These processes guarantee a reduction of up to 90% of CO2 emissions from coal-fired power plants, thus transforming coal into a fuel having low carbon content. The process on which Termokimik has decided to mainly focus its attention is the capture of CO2 by amine scrubbing.If we make a realistic reflection on the world energy balance of the future, we can but highlight how the use of coal is essential; as a matter of facts, it represents - and still will represent - one of the fundamental components of the energy mix, since it is inexpensive and abundant and since it is the backbone of the electricity network in many countries. If, moreover, we consider that, by 2030 about 53% of global emissions will be given by the production of electricity from emerging countries, with a consequent increase in emissions,

we can understand how this technology will be indispensable in a not too distant future.Enel has chosen to experiment and develop the new technology by installing a pilot plant at the Federico II Power Plant in Brindisi. This plant, whose design and construction were entrusted to Termokimik, an Italian Company which has always collaborated with Enel, is installed in side-stream configuration on one of the 660 MWe units, and will be able, through the emission regeneration by chemical solvents, to treat 12.000 Nm3/h disposing of 2.25 tons CO2 per hour.This pilot plant will be one of the largest and most sophisticated in the world, together with those already realized abroad by names such as Mitsubishi, Alstom and Fluor.We have to highlight the importance of the fact that the design and the construction of this Italian pilot plant were entrusted to Termokimik, as further confirmation of its potential to develop and offer avant-garde technologies, which can better suit the needs of the end customer and of the environment itself.

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Plant descriptionThe chemical reactions that take place inside the absorber, can be summarized as follows:

SO2 + H2O H2SO3 Absorption

CaCO3 + H2SO3 CaSO3 + CO2 + H2O Neutralization

CaSO3 + 1/2 O2 CaSO4 Oxidation

CaSO3 + H2SO3 Ca(HSO3)2 pH Control

CaSO3 + 1/2 H2O CaSO3 1/2H2O Crystallization

CaSO4 + 2H2O CaSO4 + 2H2O Crystallization

acqua industriale

fumi da trattare

slurry calcare

slurry calcare

desoxagitatore

aria compressa

assorbimento CO2

sump desox

soda

The plant is designed to treat approximately 12,000 Nm3/h of flue gas taken downstream the treatment in a Power Plant already retrofitted with catalytic denitrification system, electrostatic precipitators and desulphurization system with wet limestone-gypsum process. The capture system provides for a pre-treatment section having the purpose to further reduce the main pollutants; it is composed of a wet desulphurizer which treats mainly SO2 and SO3, followed by an electrostatic filtration system, (wet-type as well), able to treat, with considerable efficiencies, any matters present in the form of mist or aerosol, in particular SO3 and particulate.The efficiencies reached by the individual treatments adopted are design choices which are currently confidential, but we wish to underline that the presence of a pre-treatment in two stages, equipped with by-pass, will allow to better evaluate the influence of pollutants on the system under analysis.The actual capture section is based on the chemical-physical absorption of CO2 in aqueous solution of organic sorbents and on the subsequent regeneration by stripping in vapour stream. Although the use of various solutions is contemplated, the plant has been designed for use of monoethanolamine in aqueous solution (hereinafter MEA).The following describes in more detail the three main sections of the system.

Wet desulphurisationThe first section encountered by the flue gas downstream the sampling point is a desulphurizer with “wet limestone-gypsum” process. A suspension of water and finely ground limestone is introduced into a washing column in countercurrent referred to as “absorber”. This suspension is injected through a certain number of nozzles distributed across multiple stages, coming into contact with the flue gas containing SO2. This process can achieve efficiencies in SO2 reduction up to 99% and it is therefore possible to obtain, even in a commercial-size plant, SO2 levels comparable with those at the outlet of the wet column of the pilot plant, should these levels be considered an indispensable requirement for the application of the subsequent amine scrubbing.

Spraying systems on multiple levels, fed by a dedicated pump, allow the efficient absorption of sulphur dioxide.Given the presence of a desulphurizer on flue-gas line of the boiler, upstream the sampling point, the performance of this finishing section are not particularly extreme and therefore the desulphurizer is not equipped with dedicated oxidation stage, even if it has been sized, in any case, to obtain an almost complete oxidation of sulfites through natural oxidation.This will allow to drain from the absorber bottom a solution composed mainly of sulphates, avoiding any problems related to the transport of sulphites in solution, which will be transferred to the oxidation system in the boiler desulphurizer.The control of performance is made in varying the L/G ratio of the liquid in the bottom of the absorption column.The block diagram of the absorption section, together with that of the dedusting section, is shown in picture 1 here below.

assorbimentoraccolta drenaggi

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c.w

h2o demi

G4-3 D4-1

E4-3

E4-1

E4-8

D4-12

G4-15

G4-1

tank h2o

thank meatank mea

tank mea

spurghi

fumi wesp

spurghi

vapori

fumi

condensato

reclaimer

reboiler

condensatore

stripping co2

torre assorbimento co2

c.w

G4-4 D4-2

D4-4

G4-8

G4-7

Downstream the SO2 absorption section, the flue gas stream passes through a wet electrostatic precipitator. Wet electrostatic precipitators are the state of the art in the field of the technologies used to remove solid particulate up to the level of sub-micron particles, heavy metals and acid mist with efficiencies that may be as high as 98-99%.The particles entering the precipitator are distributed on the crossing surface and are negatively charged by a special system of electrodes.The flow of flue gas and charged particles pass through a system of collecting tubes duly connected to ground potential. The action of the electric field causes, therefore, a rapid migration of the charged particles towards the collecting tubes.The accumulation of particulate on the collection tubes is cyclically interrupted by the washing system which, through the injection of water, creates a liquid film which drags everything deposited on the tubes themselves into a collection basin.

CO2 Capture The flue gas at the outlet of the pre-treatment described above enter the capture section, composed of an absorption stage and an amine solution regeneration stage. The flue gas comes into contact with the rain of MEA solution that is injected in countercurrent in an absorption column, which is also equipped with water washing system, in order to reduce the leaks of MEA.The flue gas at the outlet of the absorber is then transferred to the flue gas duct of the thermoelectric unit, to be subsequently released into the atmosphere.The MEA solution in the bottom of the absorber, after preheating, enters the flash system, where the oxygen is

disengaged, thus allowing the reduction of any degradation phenomena by oxidation of the MEA solution in the stripper.The solution coming out of the flash is subsequently reintroduced from the top of the regeneration column, which occurs by heating with steam.The heat required by the regeneration of the solution is provided by a Kettle Reboiler.The regenerated solution, extracted from the Reboiler by a pump, is cooled by means of economizers which preheat the charge for the regenerator and then for the flash unit, to be subsequently sent to storage.The flue gas released from the top of the regenerator pass through the perforated plates, where the recirculation of the condenser submits them to a washing action, in order to limit the leaks of amine. Then, they pass through a water-cooled condenser followed by a vane pack, after which they are mixed with the flue gas coming from the CO2 absorption column. The two mixed streams are then transferred to the main flue gas duct of the boiler for release into the atmosphere.A reclaimer under pressure will be installed, in order to separate and drain the non-regenerable salts produced by the degradation of the MEA.Previous experiences recommend to maintain the storage tanks pressurized with nitrogen, in order to limit MEA degradation; this technique is therefore adopted in the storage of the MEA (in solution and pure), of the make-up water and of the MEA solution to filtration.The block diagram of the capture and regeneration section is shown in the picture here below.

Wet electrostatic precipitator