Average Heating Value Research Articles

Pelletized Straw for Biogas Production—Substrate Characterization and Methane Formation Potential

The use of agricultural residues in biogas plants is becoming increasingly important, as they represent an efficient and sustainable substrate alternative. Pelletizing straw can have positive effects on transportation, handling, and biogas production. In this study, different grain straw pellets from mobile and stationary pelleting plants in Germany as well as the corresponding untreated straw were characterized and investigated for their suitability for anaerobic digestion (AD). Therefore, tests on the biochemical methane potential (BMP) and the chemical–physical characterization of unpelletized straw and straw pellets were carried out. The characterization of the pellets and the straw revealed a high average total solid content of 91.8% for the industrially produced straw pellets and of 90.8% for the straw. The particle size distribution within the tested pellet samples varied greatly depending on the pelleting process and the pre-treatment of the straw. In addition, a high C/N ratio of 91:1 on average was determined for the straw pellets, whereas the average higher heating value (HHV) content of the pellets was 17.58 MJ kg−1. In the BMP tests, the methane production yields ranged from 260–319 normal liter (NL) CH4 kg−1 volatile solids (VS) for the straw pellets and between 262 and 289 NL CH4 kg−1 VS for the unpelletized straw. Overall, pelleting increases the methane yield on average from 274 to 286 NL CH4 kg−1 VS, which corresponds to an increase in methane yield of 4.3%. Based on the results, the feasibility of using straw pellets for AD could be confirmed, which can facilitate the possibility of increased biogas production from agricultural residues such as straw pellets and thus make the substrate supply more sustainable.

A Theoretical Calculation of Electrical Energy Production from the Incineration of Baghdad Municipal Solid Wastes

A theoretical investigation study was carried out to determine the requirements of establishing a steam power plant by incinerating municipal solid wastes generated from the city of Baghdad. Survey data the generated quantities of municipal solid wastes from both Al-Karth and Al-Rusafa sectors of the city were utilized to predict the theoretical possible energy production that can be obtained from the incineration of this waste under controlled parameters. Results reviled that the high heating value of Baghdad’s municipal solid wastes is of about (12.789 MJ/kg) and the possible electrical energy production in the steam power plants in Al-Karth and Al-Rusafa are (119.287 MW, 203.917 MW) respectively using a steam turbine of efficiency (25%). Resulted emissions of CO2 gases are estimated to be 4209.995 ton/day. So the emission of CO2 is the main problem of this method because of its effect on global warming but it is less effect on environment from Methane, Sulphur Oxides and Nitrogen Oxides. The quantity of plastic wastes in Municipal Solid Wastes is important in increasing their average high heating value.

Evaluation of the Thermal Energy Potential of Waste Products from Fruit Preparation and Processing Industry

In the context of a changing climate and increasing efforts to use renewable energy sources and waste materials and to green the environment, new sources and technologies for energy recovery from waste are being sought. This study evaluates the possibilities of energy generation potential from waste products of fruit species used in the food processing industry. The results indicate good potential for energy use of materials from fruit processing due to low input moisture content of around 15 wt. %, an average energy lower heating value (LHV) of 16.5 MJ·kg−1, an average low ash content of 4.9% and meeting most of the emission limits of similar biofuels. Elemental analysis and combustion residue studies indicate safe operation within existing standards. The results of our analyses and experience from similar studies allow us to recommend most of the studied waste materials for energy generation use directly in processing plants at the local level.

Biomass for dual-fuel syngas diesel power plants. Part I: The effect of preheating on characteristics of the syngas gasification of municipal solid waste and wood pellets

Indonesia has the potential to develop biomass, such as MSW and wood pellets, as a source of energy. Syngas from biomass gasification can be used as fuel for dual-fuel diesel engines in order to transition energy. We investigated the gasification of MSW and wood pellets using a downdraft reactor with a capacity of 130–144 kg in order to determine the properties of the produced syngas for use in dual-fuel syngas diesel engines. Four days are dedicated to the process of preheating biomass with sunlight. The experiment was designed with an equivalent ratio of 0.22 and an oxidation zone temperature between 700 and 900 degrees Celsius. According to the experimental results, the average lower heating value of syngas produced by the air gasification of MSW biomass was 5.85 MJ/Nm3, the cold gas efficiency was 56.6%, and the carbon conversion efficiency was 94.77%. The average lower heating value from wood pellet biomass air gasification was 5.95 MJ/Nm3, the cold gas efficiency was 67.7%, and the carbon conversion efficiency was 94.28%. Solar heating of biomass has been shown to increase the calorific value of biomass gasification to syngas.

Waste to energy: a decision-making process for technology selection through characterization of waste, considering energy and emission in the city of Ahmedabad, India.

Municipal solid waste (MSW) disposal has become major issue for the city of Ahmedabad, India. Development, concentrated population and economic growth have led to a substantial increase of MSW generation. Therefore, the objective of the study was to characterize MSW for selection of waste processing technology. To provide a solution for sustainable processing and for safe disposal of fresh MSW, Abellon Clean Energy Ltd joined forces with Ahmedabad Municipal Corporation (AMC) under Public-Private Partnership (PPP) to establish a 14.9MW advanced controlled combustion-based waste to energy (WTE) generation facility to process and dispose 1000 tons/day of fresh MSW. For waste characterization, samples (n=201) were collected from the Pirana waste dumping site using quadrate sampling method. A yearly weighted average Low Heating Value (LHV) of 9.85/kg and ash content 25.12% for unsegregated MSW makes controlled combustion with electricity generation an eligible technology. After combustion, the waste volume is reduced by 75%. The 14.9MW WTE facility replaces 417 t coal/day, reducing greenhouse gas (GHG) emissions of 300.38 tCO2eq/day through coal replacement, while avoiding 735.24 t CO2eq/day on account of landfill emissions from MSW dumping. Waste to energy is the fastest solution to reduce waste volume by generating electricity through reduction of GHG.

Manufacture of Briquettes from Baking Filter Dust (BFD) Waste and Coconut Shell Charcoal

This research utilized baking filter dust (BFD) waste obtained from PT. INALUM., which functions as a heat retainer, is processed into briquettes with the addition of coconut shell charcoal, which has not been fully utilized. This research is also to determine the optimum quality of physical and chemical properties in good briquettes to be used as an alternative fuel. This study uses the method used is the pyrolysis method with the combustion process using a closed combustion furnace and sieving using a sieve with a size of 50-100 mesh. The quality of briquettes was analyzed using the Proximate Test, Ultimate Test, and Characterization of SEM – EDX. Furthermore, the quality test of briquettes refers to SNI 016235 2000 and the Minister of Energy and Mineral Resources No. 47 of 2006; the average moisture content of briquettes is 18.65 %, the average ash content of briquettes is 4.33 %, the average volatile matter content (volatile matters) is 13.30 %, the average fixed carbon content (fixed carbon) is 63.73 %, the average heating value is 6,200 cal/g, and the sulfur content is 49.75 % on average.

ANALISIS KARAKTERISTIK BRIKET ARANG DENGAN VARIASI TEKANAN KEMPA PEMBRIKETAN

Biomass is often considered as a material that is lacking or even uneconomical. Biomass that is abundantly available in Indonesia is sawdust and coconut shell waste. This number has not been used maximally, this is because both wastes tend to be disposed of directly into the environment and can cause environmental pollution. Briquetting technology is one of method which can be implemented to increase the added value by producing briquettes. Many factors affect the quality of briquettes, one of which is the pressure of the briquette press. The pressure of the briquette press affects the durability and cohesiveness of briquettes. The aim of this research was to specify the effect of compression pressure on calorific value, ash content, and water content of briquettes. The research was conducted by varying the briquetting compression pressure, namely 1500 psi, 2000 psi, and 3000 psi. It has been done by several main stages, namely the carbonization process, the manufacture of charcoal briquettes, and test analysis. Charcoal briquettes have an average heating value of 6386.377 cal/g, 1.136% moisture content, and 6.659% ash content at a compression pressure of 1500 psi. At a compression pressure of 2000 psi, charcoal briquettes have an average heating value of 6672.601 cal/g, 1.110% moisture content, and 5.419% ash content. Meanwhile, at the compression pressure of 3000 psi charcoal briquettes have an average heating value of 6685.144 cal/g, 1.288% water content, and 6.627% ash content. Charcoal briquettes produced by varying the pressure of the briquetting press have met the quality standard of SNI 01-6235-2000 briquettes. The most optimum compression pressure for charcoal briquetting obtained in this study was 2000 psi.

KUALITAS BIOPELLET LIMBAH SEKAM PADI (Oryza sativa) SEBAGAI SALAH SATU SOLUSI DALAM MENGHADAPI KRISIS ENERGI

The purposes of this study were: 1) To analyze the characteristics of rice husk waste biopellets such as moisture content, density, ash content, flight substance content, calorific value and bound carbon content, 2) To identify the factors that influence the production of biopellets from rice husk waste. This study used a completely randomized design model with 2 (two) factors, namely variations in mesh size and variations of adhesive with 3 (three) replications. Making biopellet samples and testing the characteristics of rice husk biopellets were carried out at the Forest Products Technology Laboratory, Faculty of Forestry, Lambung Mangkurat University, Banjarbaru. The size of the powder and the amount of added adhesive as well as the interaction between the two did not have a significant effect on the value of moisture content, density, ash content, flight substance content and bonded carbon content, but had a very significant effect on heating value. The average value of moisture content ranged from 13.0771 - 14.5932%, the average density value ranged from 0.7698 g/cm3- 0.9548 g/cm3, the average value of the resulting ash content ranged from 16.5233% - 19.9633%, the average value of flying substances ranged from 57.3533% - 63.6067%, the average value of bound carbon was 6.3462% - 8.7668%, and the average heating value ranged from 2781.3800 cal/g - 3378.4600 cal/g. The factors that affect the quality of the biopelet are the process of pretreating the raw material, refining the size and mixing the adhesive.

Experimental Assessment of the Lumped Lithium Ion Battery Model at Different Operating Conditions

This study investigates the electrical and thermal characteristics of a cylindrical lithium-ion cell with an axisymmetric two-dimensional lumped model. The cell is completely discharged at 0.5, 1 and 1.5 C rates under 0, 20 and 50 °C operating temperatures. Both the open circuit voltage values and the average specific heat value of the cell are measured and used as an input to the model. The model uses the variable internal resistance approach to evaluate the voltage variation of the cell that is obtained from experimental data. A cylindrical lithium-ion cell has a spiral construction that involves multiple layers. However, these layers are assumed as a uniform material in the lumped model. The lumped model in COMSOL Multiphysics couples the heat transfer and lumped battery interfaces so it allows predicting the surface temperature of the cell during discharging processes. The experimental results point out that the operating temperature inversely affects the internal resistance and the heat generation within the cell during a discharging process. Furthermore, it is found that the capacity of the cell significantly decreases at low operating temperatures. Finally, the predicted temperature profile follows the same trend with the experimental data and is consistent at each operating condition.

Effect of Storage Time on the Physicochemical Properties of Waste Fish Oils and Used Cooking Vegetable Oils

Waste fish oils (FOs) and used cooking vegetable oils (UCOs) are increasingly becoming alternative renewable fuels. However, different physicochemical aspects of these renewable fuels, including the effect of storage, are not well-known. In this work, the effect of the storage period on physicochemical properties of selected samples of FOs and UCOs was investigated. The bio-oils were stored at 4 °C for up to five years before each experimentation. The chemical properties were characterized using capillary gas chromatography with flame ionization detection (GC-FID) and high-performance size exclusion chromatography including an evaporative light scattering detector (HPSEC-ELSD). Water contents and acid numbers of the bio-oils were determined using the Karl Fischer (KF) titration and the ASTM D 664 methods. Furthermore, the average heating values and surface tension of the bio-oils were determined. According to the results obtained, for all bio-oil types, the concentrations of polymerized triglycerides, diglycerides, and fatty acids and monoglycerides had increased during the storage periods. The physical properties of the bio-oils also showed a small variation as a function of the storage period. The overall results observed indicate that the deterioration of the physicochemical properties of bio-oils can be controlled through storage in dark, dry, and cold conditions.

Planting Density Effects on Grow Rate, Biometric Parameters, and Biomass Calorific Value of Selected Trees Cultivated as SRC

Agricultural land is mostly devoted to food production. Production of biomass is limited, as it competes for land with basic food production. To reduce land loss for growing food, biomass can be grown on marginal lands that are not usable for food production. The density of plantings have to be optimized to maximize yield potential. The presented study compares yield parameters end energy potential of six species of biomass plants (poplar, Siberian elm, black alder, white birch, boxelder maple, silver maple) cultivated in 18 planting densities from 3448 to 51,282 plants per hectare as short rotation coppice (SRC). Biomass yield parameters depended on both cultivated species and planting density. Green mass, dry mass, and shoot diameter was dropping with the increasing planting density for most tested species. Calculated yield of dry mass was dropping with increasing planting density for black alder, increasing for Siberian elm and boxelder maple. White birch and silver maple yields were optimal at moderate planting densities (25,000–30,000). White birch and boxelder maple had the highest average higher heating value (HHV). The optimal density of plantings should be chosen to best suit both the needs of cultivated species and to optimize the most important parameters of produced biomass.

Morphology characterization and chemical composition of United Arab Emirates date seeds and their potential for energy production

The seeds of a local date palm cultivar from the United Arab Emirates, Allig, were characterized in this study. Soxhlet, Folch, and CO2 supercritical extraction were employed to obtain oil from Allig date seed (DS) powder composed of 0.1–0.3 mm particles, yielding oil extraction yield percentages of 10.2%, 9.5%, and 9.8%, respectively. The main fatty acid in the extracted oil was saturated stearic acid, comprising 47.9% of the total fatty acid content. After oil extraction, the total metal content in the DSs dropped from 3.2% to 2.8%, suggesting that some metals were extracted with the oil. On the other hand, the average heating value of the DSs increased from 28.55 ± 1.84 to 29.63 ± 1.28 MJ/kg after oil extraction. The average percentages of dehydration moisture, devitalization protein and carbohydrates, devitalization lipids, and solid decomposition in the DSs before oil extraction were 1–2%, 50–55%, 10–15%, and 30–35%, respectively, whereas those for the DSs after oil extraction were 20–25%, 35–30%, 0%, and 35–40%, respectively. As expected, the lipid content dropped after oil extraction. The heat of combustion and extracted oil results indicate that palm DSs, with their relatively high energy densities, have potential as a source of energy, among other notable organic products.

Thermochemical conversion of Polyalthia longifolia leaves at different temperatures and characterization of their products

Lignocellulosic biomass is a renewable source of energy which can be harnessed to produce biofuels maintaining the carbon neutrality in the atmosphere. Thus, in this work, results of the pyrolysis of solid wastes of Polyalthia Longifolia (PL) leaves have been reported over a range of temperature from 450 °C to 600 °C at an interval of 50 °C. All experiments have been carried out three times in order to ensure repeatability and/or reduce measuring uncertainties; and the average values along with their standard deviation values are presented. The pyrolytic products have been thoroughly characterized by several advanced characterization techniques such as FTIR, GCMS, NMR, XRD, SEM, TGA, etc. as applicable to different products in addition to their physical and fuel properties. Further, the physical and fuel properties are reported for both individual organic and aqueous phases after separating liquid pyrolysis product; as well as based on raw liquid product obtained by pyrolysis before separating into organic and aqueous phases. The average higher heating value of organic phase bio-oil is varying in the range 21.74–24.28 MJ/kg for different pyrolysis temperatures. The moisture content of organic phase bio-oil varies between 0.36 mass % and 8.88 mass % over the temperature range of this study. The pH of organic phase bio-oil is in the range of 5.80 to 6.04 which indicate that the bio-oil is only marginally acidic; and further this range of pH is far better than their counterparts of open literature. From the GCMS analysis of bio-oil samples, it is found that phenol, 2,6-dimethoxy (syringol) is present with highest area % of 22.71 for the case of 600 °C pyrolysis temperature. Finally, the bio-oils produced from the pyrolysis of PL leaves are of good quality in terms of moderately large HHV, pH and low moisture content.

Improved CO2 adsorption onto chemically activated spherical phenol resin

This study reveals the significant improvement of adsorption capacity of carbon dioxide (CO2) onto spherical phenol resin (PR) activated by potassium hydroxide (KOH), designated KOH6-PR. Experiments were performed using a gravimetric adsorption measurement instrument for the wide range of temperatures 20–70 °C and pressure up to 7 MPa. The measured excess uptakes were found steadily increase up to 5.7 MPa at 25 °C and reached the value of 1.69 g g−1. After that, a declining trend was observed, which is corrected by the adsorbed gas density and pore volume of the adsorbent. The measured isotherm data were examined using the modified Dubinin-Astakhov (D-A) model, and the Tóth model within a 3.7 % root mean square deviation (RMSD). The maximum CO2 adsorption capacity of microporous KOH6-PR was found 2.36 cm3 g−1 using the modified d-A model. The adsorption capacity showed more than 50 % enhancement compared to the widely used Maxsorb III. The average value of heat of adsorption is calculated employing the Clausius-Clapeyron and the modified d-A equations. The cooling performance of an adsorption cycle using the KOH6-PR/CO2 pair is predicted. These analyses are necessary for utilizing CO2 as a refrigerant in adsorption heat pumps and gas storage applications.

HEAT ANALYSIS OF PALM OIL MESOCARP BRICK (FIBER ELAEIS GUINEENSIS JACQ) USING ADHESIVES FROM TAPIOCA, SAGU, ARPUS

Briquette is charcoal which is further processed into solid form with the aim of having a more attractive appearance and packaging, which is used for daily alternative energy as a substitute for kerosene and LPG. In this study, the manufacture of briquettes uses three types of adhesives, namely: tapioca flour, sago, and arpus. The purpose of this study is to determine the effect of the type of adhesive used on oil palm fiber briquettes to determine the effect of the type of adhesive on oil palm fiber briquettes on the burning time. The results show that the use of adhesive types on oil palm fiber briquettes affects density, combustion rate, heat value, and ash content. For the type of tapioca adhesive 15% composition has the highest average density of 0.198 gram / cm3, the highest average combustion rate for the type of tapioca flour adhesive is 20%, i.e. 0.0021 gram / second, the highest average heating value for the composition of arpus adhesive 10%, and the lowest average ash content of the composition of arpus adhesive 10% by 16.8%.

Characterization of fecal sludge as biomass feedstock for thermal treatment in the southern Indian state of Tamil Nadu.

Background: Transformative sanitation technologies aim to treat fecal sludge (FS) by thermal processes and recover resources from it. There is a paucity of data describing the relevant properties of FS as viable feedstock for thermal treatment in major geographical target areas, such as India. Methods: This study characterized FS collected from septic tanks in two cities located in the Indian southern state of Tamil Nadu. FS samples were obtained at the point of discharge from trucks in Tiruppur (n=85 samples) and Coimbatore (n=50 samples). Additionally, biosolids obtained from sewage treatment plants (STP) in the cities of Coimbatore and Madurai were characterized. Total solids (TS) were measured, and proximate and ultimate analysis were conducted according to methods used by the fuel industry. Additionally, the ash content was analyzed for heavy metal using standard methods. Results: The average higher heating value (HHV) across all FS samples in Tiruppur (13.4 MJ/kg) was significantly higher than in Coimbatore (5.4 MJ/kg), which was partially attributed to the high ash content of 69% in the latter samples. The HHV of the biosolids samples ranged from 10 to 12.2 MJ/Kg. The average total solids (TS) content for FS was 3.3% and 2.0% for Tiruppur and Coimbatore respectively, while the median TS content for the two cities was 2.3% and 1.2%. The heavy metal content of the ash was found to be below the thresholds for land disposal. Conclusions: This is one of the first studies that has systematically characterized the calorific and mineral content of septage and biosolids in several cities in India. We expect these data to serve as input data in the design of thermal processes for fecal sludge treatment.

Characterization of fecal sludge as biomass feedstock for thermal treatment in the southern Indian state of Tamil Nadu

Background: Transformative sanitation technologies aim to treat fecal sludge (FS) by thermal processes and recover resources from it. There is a paucity of data describing the relevant properties of FS as viable feedstock for thermal treatment in major geographical target areas, such as India. Methods: This study characterized FS collected from septic tanks in two cities located in the Indian southern state of Tamil Nadu. FS samples were obtained at the point of discharge from trucks in Tiruppur (n=85 samples) and Coimbatore (n=50 samples). Additionally, biosolids obtained from sewage treatment plants (STP) in the cities of Coimbatore and Madurai were characterized. Total solids (TS) were measured, and proximate and ultimate analysis were conducted according to methods used by the fuel industry. Additionally, the ash content was analyzed for heavy metal using standard methods. Results: The average higher heating value (HHV) across all FS samples in Tiruppur (13.4 MJ/kg) was significantly higher than in Coimbatore (5.4 MJ/kg), which was partially attributed to the high ash content of 69% in the latter samples. The HHV of the biosolids samples ranged from 10 to 12.2 MJ/Kg. The average total solids (TS) content for FS was 3.3% and 2.0% for Tiruppur and Coimbatore respectively, while the median TS content for the two cities was 2.3% and 1.2%. The heavy metal content of the ash was found to be below the thresholds for land disposal. Conclusions: This is one of the first studies that has systematically characterized the calorific and mineral content of septage and biosolids in several cities in India. We expect these data to serve as input data in the design of thermal processes for fecal sludge treatment.

Gasification of Eucalyptus Wood Chips in a Downdraft Gasifier for Syngas Production in South Africa

ABSTRACT The present research article aims to study the gasification of eucalyptus as wood chips for syngas production and its thermogravimetric analysis (TGA) in a nitrogen atmosphere. The eucalyptus wood chips were sourced from a sawmill industry, cut into desired sizes and subjected to gasification in a downdraft gasifier using air as the oxidizing agent. The compositions of the syngas were measured using non-dispersive infrared gas sensors and a palladium/nickel (Pd/Ni) gas sensor. Thermogravimetric analysis was carried out under 20°C/min heating rate using a Perkin-Elmer thermogravimetric analyzer TGA 7 and the gasification zones temperatures were monitored using thermocouples. An average higher heating value (HHV) of 6.08 MJ/Nm 3 containing predominantly of hydrogen, carbon monoxide and methane was obtained from the eucalyptus syngas. The volumetric compositions of the syngas produced varied from 22.3% - 22.5% for hydrogen, 22.3% – 24.3% for carbon monoxide, 1.9% - 2.1% for methane, 9.8% - 10.7% for carbon dioxide and 41.5% – 42.9% for nitrogen. Nitrogen composition was highest due to the use of air as the oxidizing agent. The study have successfully demonstrated gasification as an alternative technology for conversion of waste to energy.

Status, characterization, and potential utilization of municipal solid waste as renewable energy source: Lahore case study in Pakistan

With rapid increases in population and urbanization, uncontrolled municipal solid waste (MSW) is a threat to public health and environmental safety. In this study, we explore its generation, treatment, and characteristics of physical/chemical composition and assess the potential of MSW as a renewable energy source in Lahore, the second largest city in Pakistan. Based on the average generation rate of MSW (i.e., 0.65 kg/capita/day), the daily production of MSW in this city would reach 7150 tons/day. However, its disposal in a safely engineered way has been restricted due to the lack of: (a) pre-planning, (b) infrastructure, (c) political will, and (d) public awareness. Various samples of MSW considering socio-economic structure were collected. The physical components of MSW in Lahore were found to be in the descending order of biodegradable, nylon plastic bags, textile, diaper, and paper. The inductively coupled plasma optical emission spectroscopy (ICP-OES) technique was used to determine the heavy metal content and leachability of the MSW components to check for the environmental contamination risk. The proximate and ultimate analysis of this MSW was also carried out along with its heating values. The average high heating value of MSW was measured as 14,490 kJ kg−1. Energy recovery potential of 48 MW was assessed further from 2000 tons of MSW/day. The results of this study should be helpful for policy makers to establish a MSW management strategy for the potential renewable energy alternative.

Characterization of Municipal Solid waste’s Potential for Power Generation at Mekelle City as a Waste Minimisation strategy

ABSTRACTWaste to energy concept is one of the best methods, which not only consider the environment but also generate energy from municipal solid waste (MSW). Generation of MSWs at Mekelle city, Ethiopia, has grown steadily mainly due to migration of people from rural areas. However, the waste has not been managed and utilised as a useful resource due to lack of awareness and proper technology in the city. The objective of this study was to measure the heat content of solid waste generated in the city. Measurement of heating value was performed on collected samples using bomb calorimeter and Dulong’s formula. The average heating values obtained from the experimental analysis were 17,001 kJ/kg. The energy content obtained from the elemental composition of waste using Dulong’s formula was 16,853 kJ/kg. These results indicate that it could be possible to generate 8.7 MW of power from the solid waste composition represented by the sample; it is a good potential to alleviating the power shortage and interruption problems in the city. The results of this study could be used for design considerations in the selection and establishment of waste to energy technology in Mekelle city.