1/2017

The process of high-temperature carbonate loop for the CO2 removal from flue gas or waste gases has been intensively developing for approximately ten years, all over the world. In the Czech Republic are good conditions for its future industrial application mainly in the sector of energy and heat production and in the cement and metallurgical industry sectors. There are also large deposits of limestone of a high degree of purity, which is used as a sorption material in the process of carbonate loop. The advantage of this process compared to other processes developed for CO2 removal from exhaust gases and flue gases is the fact that the process of hightemperature carbonate loop operates at temperatures in the range of 650 to 900 ° C and most of the waste heat produced in the process can be used to produce superheated steam and subsequently electric energy. In the total energy balance constitutes the process of high-temperature carbonate loop in comparison with other similar processes less energy loss and a smaller decrease in net electricity production and heat efficiency. The first systematic research of high-temperature carbonate loop process in the Czech Republic started in 2015 at UCT Prague, Czech Technical University Prague and NRI Řež in the framework of the project "Research high-temperature sorption of CO2 from flue gas using carbonate loop" (NF-CZ08-OV-1-005-2015), which is supported by a grant from Norway-CZ08 Program "pilot studies and surveys for CCS technologies". The article describes the main research activities carried out by all project partners, equipment used to the research of this technology and the main results achieved. 

The aim was to determine the quantity of the released carbon monoxide during storage of Bílina lignite in storage bunker of fluidized bed boiler, where due to technological arrangement occurs, aside unwanted sticking to the walls associated with the temperature increase in the release of unwanted toxic carbon during the oxidation of lignite with air. Because the storage of coal under controlled technological conditions occur simultaneously storing raw, pieces lignite and dust sucked from the grinding process, the long-term measurements taken for pulverized and pieces of lignite. The temperature increase of coal from 50 to 80, respectively at 100 °C led to an increase in the concentration of carbon monoxide from about 400 to 1000 and 1600 ppm for pulverized lignite and from about 500 to 1500 and 2000 ppm for pieces of lignite. Maximum production of carbon monoxide in all observed cases was shown always approximately an hour after the start of temperature increase.

Continuing decline of CO concentrations in the long-term warming corresponded to an average of about 100 ppm per week. Weight of transformed carbon from the lignite to CO gas during the whole model warming ranged from about 100 to 500 g/t of lignite.

Value of compression factor has a significant impact on the conversion of transmitted gas volume and the delivered energy in the natural gas transmission stations under reference conditions. At present the calculation of the compressibility factor in the gas industry is performed by the calculation methods according to ČSN EN ISO 12 213: Natural gas - Calculation of compression factor. Equations of these methods (AGA 8 - DC92 and SGERG 88) are based on virial development of the equation of state. Another mentioned method is GERG 2008, which is currently the most advanced method for calculating the compressibility factor based on the Helmholtz free energy, but at the moment it is not being used in practice in Czech Republic. The article describes the different calculation methods for the calculation of the compressibility factor of natural gas.

The paper focuses on technical aspects of using high temperature sorption of carbon dioxide on the principle of carbonate loop for mitigation the emissions of this greenhouse gas from thermal waste treatment.

In the study the two most important ways of waste combustion are highlighted, namely MSW burning in grate incinerators, widespread installed in municipal waste-to-energy plants, and incineration of wastes in cement rotary kilns. The paper discusses design of particular technologies, physico-chemical conditions of the process and it puts them into the context with the results of the own research of sorption properties of selected substrates. From the available data, following conclusions are drawn regarding the number of installations for which the method of cyclical regenerative CO2 capture could be successfully deployed.

The first third of the article is devoted to the technical description of four large municipal waste incinerators, operated in the territory of the Czech Republic (Prague, Pilsen, Liberec and Brno). Attention is paid to the main factors determining usage of high temperature carbonate loop: temperature achieved, presence of steam source, age and lifetime of the facility (assessing profitability of retrofit). The next part of the study summarizes current carbon dioxide emissions, generated by the burning of wastes in the Czech Republic, that could be eliminated by implementation of CO2capturing methods. The last part of the article summarizes main principles and technological parameters of cement works that are, according to laws and directives, permitted to co-incinerate wastes.

The facilities are evaluated according to the same criteria as before. It is discussed that the rotary kilns in cement works use higher combustion temperatures and also the exhaust gas cleaning system operates on a different principle than on standard incinerators (e.g. in the ERFs).

On the basis of the own laboratory experiments following approach was proposed for discussion. Residual sorption capacity, given due to presence of thermally decomposable carbonates in the fly ash from the ESP or hose filters, can be advantageously utilised for CO2 pre-separation.