Çimento endüstrisinde kullanılan ön ısıtıcı slikon reaktörlerin deneysel incelenmesi

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Siklonlar, önısıtıcı Siklonlar Önısıtıcı siklon reaktörler çimento üretim tesislerinin önemli bir parçasını oluşturmaktadır. Döner finmn ısıl yükünü azaltmak ve böylece enerji tasarrufu sağlamak üzere çimentonun hammaddesi farinin belirli bir sıcaklığa kadar ısıtılması gerekir. Bunun için döner fırından çıkan sıcak gazlardan yararlanılır ve gazm taşıdığı ısı enerjisinin önemli bir bölümü çok kademeli olarak tasarlanan önısıtıcı siklon reaktörlerde farine geçirilir. Böylece klinker hammaddesi olan farinin miktar bakımından hemen hemen üçte biri kalsinasyon sıcaklığına kadar ısıtılmış olur. Dolayısıyla önemli bir ısı tasarrufu sağlanarak sistemin ısıl verimi yükseltilir. Bu öneminin yanında, ön ısıtıcı siklon reaktörler, günümüze kadar, ısı geçişi ve akışkanlar dinamiği bakımından yeterince incelenmemiştir. Ayrıca konuyla ilgili verilerin önemli ticari değerlerinin bulunması, bunların literatürde kapsamlı olarak yer almaması gibi bir sonucu doğurmuştur. Siklon performansına etkisi olan temel parametreleri siklonun geometrik yapışma belirleyen, boyutsal oranların yanında, işletme parametreleri, gaz debisi, gaz giriş/çıkış sıcaklıkları, gaz yoğunluğu, siklondaki basmç düşümü, hammadde konsantrasyonu ve gaz akımının siklondaki hız dağılımı sayılabilir. Burada siklonun sıcak gazlardan farine yüksek bir ısı geçişini, düşük basınç kayıpları ve yüksek ayrışma (tutma verimi) ile gerçekleştirme istenir. Bu çalışmada, siklon geometrik özellikleri ile çalışma koşullarının siklon performansı üzerindeki etkilerini incelemek üzere deneyler yapılmıştır. Deneyler için, önısıtıcı siklon reaktör olarak Humboldth tipi [2] bir siklon, seçilmiştir. Bu önısıtıcı siklon bir kademeli olarak incelenmiştir. Siklon dalma borusu derinliği, gaz giriş sıcaklığı, gaz giriş hızının ve farin konsantrasyonunun, araştırma sonuçlarına göre performans üzerinde önemli etldlerinin bulunduğu ve ön ısıtıcı siklon tasarımında mutlaka dikkate alınması gerektiği anlaşılmıştır. Bununla beraber daha genel sonuçlara varabilmek için çeşitli deney koşullarında ve siklon tipleriyle deneyler yapmaya gereksinim vardır. Buradan elde edilen deneysel bulguların, kurulacak teorik modellere önemli bir katkı yapacağı açıktır.AN EXPERIMENTAL INVESTIGATION ON THE PRE-HEA- TER CYCLONE REACTORS UTILISING IN CEMENT INDUSTRY SUMMARY Keywords: Cyclones, Pre-heater cyclones The most important part of cement production line is the rotary kiln. Before entering the rotary kiln, raw material, namely dust, should be heated to a certain temperature to reduce its heat load. To do this, multistage pre-heater type of cyclones have been widely used in cement industry to recovery heat energy of hot gas. The heat is, then, used in preheating of dust which is the raw material of the cement. Thus the dust is heated until its calcination temperature is reached. Therefore, a large amount of heat energy is saved. Nevertheless, the cyclones used as a pre-heater in cement processes have scarcely been investigated in view of heat transfer and fluid dynamics, up to now. In addition, most data in the field are not available in the open literature due to their commercial values. The variables which affect the cyclone performance are; hot gas flowrate, inlet/exit gas temperatures, gas density, pressure drop in the cyclone, geometrical specifications of the cyclone, raw material concentration and the velocity distribution of the gas flow. It is obvious that a study concerning pre-heater cyclone should be simultaneously elaborated with heat transfer and fluid dynamics principles. In this work, experiments were conducted to determine the effects of geometrical properties and operating conditions of the cyclone characteristics, on the pre-heater. A type of Humboldth cyclone with with one stage was used over the experiments. Test results have shown that the parameters mentioned above have a considerable impact on the pre-heater characteristics and must be consider in design considerations. However, for a general conclusion, more detailed studies should be conducted at various test conditions. XI

Energy auditing and recovery for dry type cement rotary kiln systems - A case study

Cement production has been one of the most energy intensive industries in the world. In order to produce clinker, rotary kilns are widely used in cement plants. This paper deals with the energy audit analysis of a dry type rotary kiln system working in a cement plant in Turkey. The kiln has a capacity of 600 ton-clinker per day. It was found that about 40% of the total input energy was being lost through hot flue gas (19.15%), cooler stack (5.61%) and kiln shell (15.11% convection plus radiation). Some possible ways to recover the heat losses are also introduced and discussed. Findings showed that approximately 15.6% of the total input energy (4 MW) could be recovered. (C) 2004 Elsevier Ltd. All rights reserved

Second law analysis of water flow through smooth microtubes under adiabatic conditions

In the study, a second law analysis for a steady-laminar flow of water in adiabatic microtubes has been conducted. Smooth microtubes with the diameters between 50 and 150 mu m made of fused silica were used in the experiments. Considerable temperature rises due to viscous dissipation and relatively high pressure losses of flow were observed in experiments. To identify irreversibility of flow, rate of entropy generation from the experiments have been determined in the laminar flow range of Re = 20-2200. The second law of thermodynamics was applied to predict the entropy generation. The results of model taken from the literature, proposed to predict the temperature rise caused by viscous heating, correspond well with the experimental data. The second law analysis results showed that the flow characteristics in the smooth microtubes distinguish substantially from the conventional theory for flow in the larger tubes with respect to viscous heating/dissipation (temperature rise of flow) total entropy generation rate and lost work. (C) 2010 Elsevier Inc. All rights reserved

Geometrical optimisation of vehicle shock dampers with magnetorheological fluid

Magnetorheological (MR) dampers have attracted interest from suspension designers and researchers because of their variable damping feature, mechanical simplicity, robustness, low power consumption and fast response. Therefore, optimisation of such devices is of particular interest to achieve optimal vibration control. This study deals with the geometrical optimisation of an MR shock damper using Taguchi experimental design approach. The optimal solutions of the MR damper were evaluated using analytical equations, which give the dynamic range of the damper under consideration. Optimal geometrical values obtained provided most performance in consideration of other nine alternatives of Taguchi experimental design specified for the study

The longitudinal evolution of post-COVID-19 outcomes among hemodialysis patients in Turkey

Introduction: Hemodialysis (HD) patients have increased risk for short-term adverse outcomes of COVID-19. However, complications and survival at the post-COVID-19 period have not been published extensively.Methods: We conducted a national, multicenter observational study that included adult maintenance HD patients recovered from confirmed COVID-19. A control HD group without COVID-19 was selected from patients in the same center. We investigated the characteristics and outcomes in the follow-up of HD patients and compare them with the non-COVID-19 group.Results: A total of 1223 patients (635 patients in COVID-19 group, 588 patients in non-COVID-19 group) from 47 centers were included in the study. The patients' baseline and HD characteristics were almost similar. The 28th-day mortality and mortality between 28th day and 90th day were higher in the COVID-19 group than non-COVID-19 group (19 [3.0%] patients vs. none [0%]; 15 [2.4%] patients vs. 4 [0.7%] patients, respectively). The presence of respiratory symptoms, rehospitalization, need for home oxygen therapy, lower respiratory tract infection, and arteriovenous (AV) fistula thrombosis was significantly higher in the COVID-19 group in both the first 28 days and between 28 and 90 days. In the multivariable analysis, age (odds ratio [OR] [95% CI]: 1.029 [1.004-1.056]), group (COVID-19 group vs. non-COVID-19 group) (OR [95% CI]: 7.258 [2.538-20.751]), and vascular access type (tunneled catheter/AV fistula) (OR [95% CI]: 2.512 [1.249-5.051]) were found as independent parameters related to 90-day mortality.Conclusion: In the post-COVID-19 period, maintenance HD patients who have had COVID-19 have increased rehospitalization, respiratory problems, vascular access problems, and high mortality compared with the non-COVID-19 HD patients

The longitudinal evolution of post–COVID-19 outcomes among hemodialysis patients: A nationwide multicentre controlled study

BACKGROUND AND AIMS: Haemodialysis (HD) patients are at increased risk for adverse short-term consequences of COVID-19. In this study, we investigated the characteristics of chronic HD patients in the post-COVID-19 period and compared them with the control group. METHOD: We conducted a national multicentre observational study involving adult chronic HD patients recovering from COVID-19. The control HD group was selected from patients with similar characteristics who did not have COVID-19 in the same center. SARS-CoV-2 RT-PCR negative patients and patients in the active period of COVID-19 were not included. RESULTS: A total of 1223 patients (635 COVID-19 groups, 588 control groups) were included in the study from the data collected from 47 centres between 21 April 2021 and 11 June 2021. The patients' baseline demographics, comorbidities, medications, HD characteristics and basic laboratory tests were quite similar between the groups (Table 1). 28th-day mortality and between 28th day and 90th day mortality were higher in the COVID-19 group than in the control group [19 (3.0%) patients and 0 (0%) patients;15 (2.4%) patients and 4 (0.7%) patients, respectively]. Presence of respiratory symptoms, rehospitalization, need for home oxygen therapy, lower respiratory tract infection and A-V fistula thrombosis were significantly higher in the COVID-19 group in the first 28 days of illness and between 28 and 90 days. Mortality was significantly associated with preexisting COVID-19, age, current smoking, use of tunneled HD catheter, persistence of respiratory symptoms, rehospitalization, need for home oxygen support, presence of lower respiratory tract infection within 28 days and persistence of respiratory symptoms. CONCLUSION: In the post-COVID-19 period, mortality, rehospitalization, respiratory problems and vascular access problems are higher in maintenance HD patients who have had COVID-19 compared to control HD patients. (Table Presented)