Paliva (Fuels) is a scientific journal issued quarterly by the Faculty of Environmental Technology, ICT Prague. Fuels publishes papers on a broad range of topics covering exploitation, processing, upgrading, and utilization of various types of fuels, and power engineering.
Current issue
4/2020
Halogen Derivatives in Pyrolyzed Plastics
Marek Staf, Vít Šrámek, Michael Pohořelý
The article deals with the issue of waste plastics pyrolysis leading to the industrially applicable liquid and gaseous products. The problem of thermally labile halogenated compounds, present in the feedstock, is discussed.
The introductory part focuses mainly on halogenated flame retardants and their toxicological and environmental risks. In comparison with the standard recycling of waste plastics, pyrolysis with subsequent material utilization of the liquid product is mentioned as a promising method capable to solve the problem with the presence of halogen derivatives. The following second part of the article summarizes studies searching suitable methods for removing inorganically and organically bound chlorine and bromine from pyrolysis organic condensates - i.e. pyrolysis oils.
Dehalogenation processes are divided into several categories according to the nature of the process and also according to the method of application of the respective reagent, catalyst or sorbent. Within each group, the results published in the available literature are briefly summarized. When commenting on them, the main emphasis is placed on the applicability of the obtained pyrolysis oils as raw materials for refinery processing and new polymers production.
At the end of the article, a plan of experiments is outlined, which will be carried out during the research of the issue by the authors team. The space is mainly dedicated to the construction of two laboratory apparatuses that has been developed for this purpose.The first batch apparatus working with a vertical retort allows studying of gaseous, liquid and solid pyrolysis products at various temperatures. The second, continuously operating apparatus, is designed to test the efficiency of hydrogen halides adsorption from gaseous mix-tures at high temperatures.
The third apparatus designed for the research purposes is a catalytic continuous system enabling to study the decomposition of organic halogen derivatives. The results of the experiments will be published continuously after their verification with sufficient reproducibility.
Keywords: flame retardants; toxicity; food; recycliing; pyrolysis
4/2020 - pages 136 - 148DOI: 10.35933/paliva.2020.04.01
The Application of an Expansion Turbine in the Production of Expanded Aggregates
Tomáš Hlinčík, Karel Ciahotný, Petr Buryan
The research into the expansion of Cypris clay from the overburden rocks of the Družba brown coal open-pit mine in North Bohemia has proven that targeted expansion enables good use of the thermal energy of hot aggregates, which has not yet been fully exploited. The integration of an electricity production expansion turbine into the production line and the use of residual gas heat in the turbine cycle can reduce production costs. The article assesses two possible solutions for the integration of the expansion turbine into the technological line, namely with an open and closed working cycle using various gaseous media. In both cases, the proportion of the energy usable for electricity generation in the expansion turbine cycle has been calculated along with the possible fuel savings in the rotary kiln by using combustion air preheated to a high temperature by the residual heat of the gas from the turbine gas cycle.
Keywords: Cypris clay; expansion; turbine; waste heat
4/2020 - pages 149 - 154DOI: 10.35933/paliva.2020.04.02
Influence of the Calcination Temperature on the properties of The Alumina as Catalyst Support for Catalysis
Tomáš Hlinčík, Veronika Šnajdrová, Veronika Kyselová
Alumina is commonly used in industrial practice as a catalyst support and it is made from boehmite. Depending on the calcination temperature, this mineral is transformed into various crystalline modifications which have different physical and chemical properties. For this reason, the following parameters were determined at different calcination temperatures: length, width, material hardness, specific surface area and total pore volume. The results show that with increasing calcination temperature there have been significant changes which may be important when using the material as a catalyst support, e.g. in the preparation of catalysts or in the design of cat-alytic reactors. The specific surface area, which decreases in the temperature range 450–800 °C, is an important parameter for the preparation of catalysts, so it is appropriate to choose a temperature of 600 °C, when the specific surface area is above 200 m2·g-1. The effect of calcination temperature on the structural transitions of boehmite was also monitored. The results showed that γ-Al2O3 has the most suitable properties as a catalyst sup-port in the temperature range 450–800 °C.
Keywords: alumina; katalyzátor; boehmite
4/2020 - pages 155 - 161DOI: 10.35933/paliva.2020.04.03
Oxy-fuel combustion of natural gas: A review
Tomáš Hlinčík, Karel Ciahotný, Petr Buryan
The article compares newly developed methods of natural gas combustion through oxy-fuel technologies. It describes in detail the basic technological differences and ordering of technological parts for five different cycles using carbon dioxide and steam as a working medium in expansion turbines in electricity production. Among the procedures using steam as the working medium, attention is focused on GRAZ and CES cycles. In oxy-fuel procedures utilising carbon dioxide produced by natural gas combustion, the focus is on COOLCEP, MATIANS and COOPERATE cycles. For each cycle described, the respective operating conditions and principles are given. Additionally, detailed process diagrams are also provided. Important advantages of all of these cycles include the possibility of the combustion of not only liquefied natural gas but also other gaseous fossil fuels, whose introduction into production is not very time-consuming, and the possibility of connection to power distribution network within a relatively short period of time.
Keywords: oxy-fuel, natural gas, CCS, carbon dioxide
4/2020 - pages 162 - 168DOI: 10.35933/paliva.2020.04.04
Vřesová: Brief history and evaluation of pressure coal gasification
Petr Mika
The Vřesová Gasworks began operation in 1969, supplying town gas to a gas system of the then Czechoslovakia and was at the time the largest gas producer in the country. This Gasworks produced last cubic metres of syngas for syngas-fired combined cycle blocks in August 2020. It is so just shortly after 50 years when put this plant in operation.
This article bring an retrospect and small evaluation of technology, achieved parameters and possibilities which the classic coal gasification was offered.
Brown Coal Gasification in Vřesová. The gasification takes place in 26 water-jacketed fixed-bed gasifiers with an internal diameter of 2.7 m. The particle size of the graded brown coal is 3 to 25 mm; the gasification rate is 4 to 8 kg steam/m³(n) of oxygen. In the counter-current arrangement, the gasification occurs in several zones (see Figure 1).
In the bottom zone there is an ash layer several decimetres high where the steam-oxygen gasification agent is preheated by the hot ash and evenly distributed over the full cross-section of the gasifier. In the subsequent oxidation zone, oxygen and carbon react vigorously re-sulting in generation of carbon dioxide. The heat genera-ted is used for supporting a number of gasification reacti-ons occurring in the next zones of the gasifier.
The carbon dioxide and steam gases rich leaving the oxidation zone, enter the reduction zone where the bulk of heterogeneous reactions of carbon occur generating primarily CO, H2 and CH4. This is also the point in the reactor where the CO shift conversion of steam and CO to CO2 and H2 takes place (Tab. 1, react. 9).
The last two zones in the direction of the generated gas flow are the carbonization and drying zones. In the carbonisation zone, the primary tar is generated from the organic portion of the coal. In the drying zone, water is evaporated from the coal before the latter enters the carbonisation zone.
Tar, Phenol and Ammonia Recovery. The raw syngas leaves the gasifier at pressure of 2.7 MPa and a temperature after the pre-cooler of about 200 - 220 °C. This gas was subsequently cooled to about 30 °C prior to entering the Rectisol unit. In the course of this cooling, both water and a rich mixture of organic substances condense out of the raw syngas. This condensate was directed to an atmospheric pressure gravitational separation device where the tar was separated from the aqueous phase (raw phenol water); heavy tar slurries also sedi-ment.
After the gravitational tar separation, the phenol water was subject to dephenolisation by butyl acetate ex-traction. A phenol concentrate was the resulting product. The dephenolised water was then cleaned of ammonia in a stripper and after that directed to biological treatment. The finished water was used for floatation removal of slag and ash from both the conventional power boilers and the gasifiers. Ammonia was further concentrated to 99.8 %. Part of the ammonia obtained in wastewater pu-rification was used in the Selective Catalytic Reduction (SCR) unit of the thermal incinerator which was used to treat lean flash gas from the Rectisol unit.
Liquid by-products from the gasification therefore include coal tar, phenol concentrate and liquid ammonia. In addition crude naphtha was recovered from remaining hydrocarbons entering the Rectisol acid gas removal unit and sulphuric acid was produced from the acid gas. Amount of by-products from the gasification 1969 – 2020 see in Tab. 3. Other organic substances separated during the process of ammonia removal could also extend this list: these were substances that were stripped from the phenol-free water along with ammonia, and separated in the process of the liquid ammonia refining.
Rectisol Acid Gas Removal. The cooled raw gas from the gasification unit was further treated to remove various impurities using a selective Rectisol process, which uses chilled methanol as solvent.
The raw gas entering the Rectisol unit was first wa-shed by a mixture of water and hydrocarbons and was thus cleansed of the crude naphtha, ammonia, and HCN and also of any ash remnants that could have abrasive effects in the subsequent process.
The gas was then washed with cold methanol to re-move H2S, COS and lower thiols. The total sulphur con-tent of the clean gas was about 13 mg/m³.
In the original town gas application, the Rectisol unit included a second stage, in which carbon dioxide was removed down to a level of 5% vol. This stage was bypassed and most of the CO2 was left in the pure gas, so that it could have to perform mechanical work in the gas turbine expander section. The utility consumption of the Rectisol unit was also reduced. In addition to the effi-ciency advantage of leaving the CO2 in the gas, it also served to provide a very effective diluent to the syngas, which reduced the formation of nitrogen oxides during combustion in the gas turbine.
The pressure of the clean syngas downstream the Rectisol unit was 2.1 – 2.5 MPa, which allows it to be used in the gas turbine without additional compression. The gas was practically sulphur free and did not contain any nitrogenous substances. This makes it an environ-mentally friendly fuel for the subsequent power plant.
Wet Sulphuric Acid. The concentrated acid gas contained between 2 and 7 vol% H2S and was directed to a 100 t/d WSA wet sulphuric acid plant where the sulphur compounds were burned to SO2 and then converted to SO3 in a catalytic process. Sulphur trioxide then reacted with water vapour producing H2SO4 that condenses as a highly marketable 96% acid product. The WSA unit was started up in 1994. Prior to this the acid gas was simply incinerated.
Thermal Incinerator. In addition to the main acid gas stream a small lean flash gas stream containing less than 1% H2S leaved the Rectisol plant. This was treated in a thermal incinerator.
Emissions. Sulphur oxide (SOx) emissions were governed by the sulphur slip from the Rectisol unit and were less then 0.2 mg/m³ in the gas turbine flue gas.
Nitrogen oxide (NOx) emissions generated from nit-rogen species in the fuel (fuel NOx) are essentially nil, since the nitrogenous compounds in the coal were trans-formed to ammonia and hydrogen cyanide in the gasifi-cation process and removed in the subsequent gas tre-atment.
NOx emissions are therefore almost completely de-termined by the generation of thermal NOx in the gas tur-bine burner. The CO2 retained in the syngas provided a good diluent to reduce flame temperatures. In Vřesová, steam injection into the flame is used to provide additio-nal temperature reduction.
The limit (and guaranteed) content of nitrogen oxi-des in the flue gas, is 45 ppm at 15 % oxygen which meets the air protection standards with a large reserve.
New Liquids Gasifier. Given the economic attracti-veness of the concept, a new liquids gasifier has been in-stalled. The selected technology was a Siemens SFG (for-merly Future Energy GSP) entrained-flow gasifier.
The feedstock was gasified with oxygen and steam under a pressure of 2.8 MPa and at an overall reaction temperature of about 1,400 °C, which results in a raw syngas containing H2, CO, and CO2 as the major compo-nents. Basically, it was the similar to the syngas from the fixed-bed gasifiers in which the content of methane or other hydrocarbons is almost zero.
The major feedstock for the new gasifier was coal tar from the fixed-bed gasifier. Additional fuels were phenol concentrate, crude naphtha and other organic sub-stances. Initially each feed was to be injected separately via a separate burner. In the meantime all the feeds were pre-mixed before being fed to the gasifier.
The hot raw syngas leaved the reactor at the bottom through the slag outlet and entered the quench chamber, which is integral with the reactor. Water sprayed into the quench chamber through nozzles cools the syngas, removed slag particles and concurrently saturated the gas with steam.
The cooled raw gas then leaved the quench chamber and entered the crude gas washer where it was subject to additional washing. Then, it was coming into the cooling and condensation tower, which was already common to the new and old technology. Here, it was mixed with the gas from the fixed-bed gasifiers.
Conclusion. Over the last 50 years, SUAS has been able to transform its Vřesová Gasworks into an important centre for clean coal technology in the Czech Republic, while simultaneously having to adapt to a deterioration in feedstock quality. Key milestones have been the tripling of its electric power output with two syngas-fired combined cycle plants including their integration into the combined heat and power system, the installation of the wet sulphuric acid plant and the addition of the SCR to the thermal incinerator using internally generated ammonia.
SUAS has been able by installing a liquids gasifier to generate additional syngas from the coal tar and other organic materials. The installed equipment (including fix-bed gasifiers) was also capable of processing other solid (by co-gasification) and liquid wastes from outside the Vřesová complex, which offered a further opportunity for environmental improvements.
Unfortunately, the company owners made a decision to terminate the operation of this last pressure Gasworks – not only in Czechia, but in the Europe too. So it wasn´t possible to make use of potential which the Vřesová Gasworks offered.
Keywords: gas plant; coal gasification; generator; combined cycle power plant
4/2020 - pages 169 - 180DOI: 10.35933/paliva.2020.04.05
Pellets based on biofuels
Petr Buryan, Diana Sedláčková
Laboratory analyzes showed that the wood chips had a higher bulk density and a significantly lower ash content than wood pellets produced by the company technological process company Pelletia-cz. using an annular granulator with a pellet outlet temperature of 80-90 ° C. The water content and calorific value of the wood chips were slightly lower than that of the wood pellets. The content of volatile combustibles and the elemental composition of the two compared energy raw materials did not differ significantly.
On the contrary, significant differences were found in herbal pellets (from winter wheat straw, winter rye straw and from whole triticale) produced by the identical process. It was shown that both the plant material and the addition of 3 wt. clay flours (binders) affect their parameters. For example, the proportion of fine material by the addition of a binder was significantly reduced in rye (to 0.17% by weight) and triticale pellets (to 0.04% by weight). On the other hand, the disadvantage of adding clay flour as a binder additive is the increase in the ash content, which reduces the calorific value of the pellets. The heat of combustion of pellets made of wood materials was about 2.5 MJ / kg higher than that of herbal pellets. Combustion of pellets from the three types of herbs monitored produces more emissions of chlorine and nitrogen oxides contaminants than wood samples relative to wood samples. The chlorine content in ashes from herbal pellets compared to ashes from wood materials was about 50 times higher. The nitrogen content in the compared raw materials was about 5–15 times higher for herbs.
Keywords: biofuels; pellets
4/2020 - pages 181 - 188DOI: 10.35933/paliva.2020.04.06