Šilumos ūkio problemų analizė šalies regionuose

District heating (DH) companies deal with serious economic-financial problems during the transition period towards market economics. The paper investigates economic-financial situation of DH companies. Significant difference between heat tariffs and production costs, huge commercial heat supply losses has been identified with the help of simulation mathematical model. All this causes damage for the sustainable energy development. The mathematical model of the heat sector is based on the establishment of info system of the energy sector and may be used as a tool for the assessment and revision of a state policy

Investigation of Waste Biogas Flame Stability Under Oxygen or Hydrogen-Enriched Conditions

Increasing production rates of the biomethane lead to increased generation of waste biogases. These gases should be utilized on-site to avoid pollutant emissions to the atmosphere. This study presents a flexible swirl burner (~100 kW) with an adiabatic chamber capable of burning unstable composition waste biogases. The main combustion parameters and chemiluminescence emission spectrums were examined by burning waste biogases containing from 5 to 30 vol% of CH4 in CO2 under air, O2-enriched atmosphere, or with the addition of hydrogen. The tested burner ensured stable combustion of waste biogases with CH4 content not less than 20 vol%. The addition of up to 5 vol% of H2 expanded flammability limits, and stable combustion of the mixtures with CH4 content of 15 vol% was achieved. The burner flexibility to work under O2-enriched air conditions showed more promising results, and the flammability limit was expanded up to 5 vol% of CH4 in CO2. However, the combustion under O2-enriched conditions led to increased NOx emissions (up to 1100 ppm). Besides, based on chemiluminescence emission spectrums, a linear correlation between the spectral intensity ratio of OH* and CH* (IOH*/ICH*) and CH4 content in CO2 was presented, which predicts blow-off limits burning waste biogases under different H2 or O2 enrichments

Fabrication and characterization of environmentally friendly biochar anode

Electrical power generation by means of electrochemical systems utilizing wastewaters is a global energy challenge tackling technique for which a creation of novel eco-friendly electrode materials is in high relevance. For this purpose a Rhodophyta algae derived activated biochar anode bound with a flaxseeds mucilage binder (5, 10, 20, 30 wt.%) was formed and characterized by thermogravimetric, Brunauer-Emmett-Teller (BET) analysis as well as conductivity and mechanical resistance determination. Activation technique with KOH prior to carbonization at 800 °C of algae was employed to obtain biocarbon with a large surface area. The highest specific surface area of 1298.49 m2/g was obtained with the binder-free sample and had a tendency to decrease with the increase of the binder content. It was estimated that biochar anodes are thermally stable at the temperature of up to 200 °C regardless of binder concentration. The concentration of the binder on the other hand had a significant influence in anodes mechanical resistance and electrical conductance: anode with 30 wt.% of the binder had the highest compressive strength equal to 104 bar; however, the highest conductivity was estimated in anode with 5 wt.% of the binder equal to 58 S/m. It is concluded that anode with 10 wt.% mucilage binder has the optimal properties necessary in MFC utilization

Assessment of cytochrome c and chlorophyll a as natural redox mediators for enzymatic biofuel cells powered by glucose

The development of new high-power biofuel cells has been limited in the past by slow or indirect charge transfer. In this study, enzymatic biofuel cell (EBFC) systems were explored with different materials used to evaluate their applicability as redox mediators. Redox mediators of different natures have been selected for this research. Cytochrome c, Chlorophyll a, and supernatant of ultrasonically disrupted algae Chlorella vulgaris cells were examined as potential redox mediators. The effect of heparin on the EBFC was also evaluated under the same analytical conditions. The measurements of open circuit potential (OCP) and the evaluation of the current response in two modes of measurement were performed (i) during potential cycling in cyclic voltammetry measurements or (ii) at the constant potential value in chronoamperometry, and were applied for the evaluation of EBFC. Cytochrome c, Chlorophyll a, and the supernatant of ultrasonically disrupted algae Chlorella vulgaris cells-based redox mediators were efficient in the glucose oxidase (GOx) based EBFC. Electron transfer from GOx to the electrode was facilitated through the redox mediators adsorbed on the electrode. Electrodes modified with Chlorophyll a- and Cytochrome c-based redox mediators were suitable for the development of glucose biosensors. This was demonstrated by increasing the glucose concentration within 0 mM–100 mM in the system, the current density increased, and the system reached equilibrium rather faster regarding the electrochemical reaction. The power density is an important feature in revealing the action of biofuel cells. The highest power values were generated by the systems based on the application of redox-mediated Chlorophyll a and the supernatant of ultrasonically disrupted Chlorella vulgaris cells. The surface power density was about 2.5–4.0 µW/cm2. Control of a study was performed with a polished graphite electrode and the maximum surface power density was 0.02471 µW/cm2