Atıkların yüksek sıcaklıkta sürekli pirolizi için yarı-pilot ölçek yeni bir vidalı reaktör geliştirilmesi
Development of a new semi-pilot scale screw reactor for continuous pyrolysis of wastes at high temperature
- Tez No: 865213
- Danışmanlar: PROF. DR. NİLGÜN YAVUZ, PROF. DR. HASAN CAN OKUTAN
- Tez Türü: Doktora
- Konular: Enerji, Kimya Mühendisliği, Makine Mühendisliği, Energy, Chemical Engineering, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2024
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Lisansüstü Eğitim Enstitüsü
- Ana Bilim Dalı: Enerji Bilim ve Teknoloji Ana Bilim Dalı
- Bilim Dalı: Enerji Bilim ve Teknoloji Bilim Dalı
- Sayfa Sayısı: 109
Özet
Bu doktora tezinde, sürekli beslemeli, yüksek sıcaklıklı, uzun buhar kalma süreli, efektif karıştırma sağlayan modifiye ribbon vidalı ve ticari ölçeğe taşınabilmesi için yeterli kapasite bir piroliz reaktörü geliştirilme çalışmaları yapılmıştır. Dünya üzerindeki atık sorunu her geçen gün artarken, atıktan enerji üretim sistemlerinin yeteri kadar yaygınlaşamamasının nedenleri araştırılmıştır. İnsinerasyon sistemlerinde her atık için yüksek yanma verimi sağlanamamakta ve emisyon yaratmamaktır. Plastik gibi ergime sıcaklığı düşük atıklarda ise malzemenin eriyerek diğer organik maddelerin üzerini kaplayarak oksijen temasını kesmekte ve yanmamış malzemenin yanma odasını terk etmesini sağlamaktadır. Gazlaştırma sistemlerinde ise gaz hatlarındaki tar, her gazlaştırıcı tipi için tıkanma sorunları yaratmaktadır. Kesikli düşük sıcaklık piroliz sistemlerinde hem sıvı ürün hem de gaz ürün çıkması iki farklı ürün ile çalışan enerji üretim sistemleri gerektirmekte, iki farklı sistem iki ayrı sorun kaynağı olarak görülmekte ve cazibesini yitirtmektedir. Sürekli piroliz sistemleri olan akışkan yatak ve döner piroliz reaktöründe ise karışım efektifliğinden ötürü piroliz verimleri yüksek olmasına rağmen, reaktör içerisinde oluşan buharlar hızlı bir şekilde reaktörü terk ettiği için ikincil reaksiyonlar için yeteri kadar süre tanınmamakta ve yine yüksek oranda sıvı ürün çıkmaktadır. Ağırlıklı olarak gaz ürün üretmeyi hedefleyen yüksek sıcaklıklı mikrodalga destekli piroliz sistemlerinde ise sadece yüksek kaliteli elektrik enerjisinin kullanılması, sıcaklık ölçüm sorunları, reaktör gövdesinde metal gibi yansıtıcı malzemelerin kullanılamaması gibi nedenlerden dolayı, ticari büyüklükteki geleneksel ısıtmalı reaktörlerin yerini alması için sürekli mikrodalga pirolizinin daha da geliştirilmesi gerekmektedir. Sürekli piroliz sistemleri için yaygın olarak kullanılan vidalı reaktörlerde ise düşük malzeme karışım efektifliği, tıkanma ve vida mili kırılma sorunları yaşanmaktadır. Bu durumlar göz önünde bulundurularak, minimum tar ve çar, maksimum sentez gazı üretimi hedeflenerek, diğer reaktör sistemlerinin avantajlı yönleri ile vidalı reaktör sisteminin birleştirilmesi göz önünde bulundurularak yeni bir sürekli reaktör tasarım gerçekleştirilmiş, kapasitesi için de ticari ölçek için veri sağlamak amacıyla da laboratuvar içerisinde sorun yaratmadan işletilebilecek en yüksek değer çalışılmış ve 10 kg/h baz alınmıştır. Yeni reaktör sisteminin performansının test edilebilmesi için Türkiye'deki potansiyeli yüksek olan ve reaktör içerisinde birbirinden farklı etkiler yaratabilecek beş farklı atık belirlenmiştir. Çeltik sapı, arıtma çamuru, kompozit atık, fındık ve kayısı çekirdeği kabuğu ile yapılan deneyler sonucu tar üretim miktarı, sentez gazı üretim miktarı, sentez gazı üretim verimi, sentez gazı kalorifik değeri ve çar dönüşüm verimi analiz edilmiş ve literatürde mevcut olan çalışmalar ile kıyaslanmıştır. Değerlendirmeler sonucunda tar ürün çıkışının, literatürde aynı ve yakın sıcaklıklarda yapılmış tüm çalışmalardan düşük olduğu görülmüştür. Sentez gazı üretim miktarı, verimi ve kalorifik değeri de benzer çalışmalarda alınan değerlerin büyük bir çoğunluğundan daha yüksektir. Deney süresi boyunca stabil şekilde seyreden sentez gazı analizindeki %40'ı aşan hidrojen ve %25 dolaylarındaki metan oranı, saflaştırma ile hidrojen ve metan gazı üretimlerinde kullanılması için ciddi potansiyel arz etmektedir. Çar ürün çıkışı da literatürdeki çalışmalardan daha kısa süre, 15 dakika içerisinde TGA verilerinden daha düşük bir noktaya indirilmiştir. Düşük kül içerikli fındık ve kayısı çekirdeği kabuğu pirolizinden çıkan çar, tamamen uçucularından arındırıldığı için aktif karbon üretimi için potansiyel oluşturmaktadır. Buharların sıcak bölge içerisinde uzun kalma süresi ile tar ürün çıkışının en aza indirilmesi ve tozların sıcak siklon ile yoğuşma olmadan gazdan arındırılması, hatlarda tıkanma ve yapışma sorunlarının önüne geçmiştir. Çar dönüşüm verimi ve tesis uzun süre çalıştırılması rağmen bu süreç boyunca reaktör içi mekanik sorun yaşanmamış olması, geliştirilmiş vida sisteminin karışım ve iletim konusunda başarılı olduğunu göstermiştir. Ünite kapasitesi 10 kg/h gibi yarı pilot ölçek olduğu için elde edilen veriler ile ticari ölçeğe büyültme yapılabileceği için sonuçlar, atıklardan enerji üretimi konusunda verimli ve çevreci bir sistem oluşturulması için umut vaad etmektedir.
Özet (Çeviri)
In this Ph.D. thesis, a novel high temperature continuous pyrolysis reactor with modified ribbon screw conveyor was developed in order to achieve high syngas efficiency with low tar and char yield. Existing continuous gas generating reactors were examined, and good and bad aspects were analyzed. Pretests were done on a batch type rotary pyrolysis reactor and with the whole data, a novel reactor were designed and manufactured. After installation, performance tests were carried out using high potential wastes with different reactions; rice husks, sewage sludge, composite waste, hazelnut shell and apricot kernel shell. The meaning and the aim of this thesis were given in the first chapter. Briefly, the inadequacy of existing energy conversion systems is mentioned. Then the reasons of selection the materials for pyrolysis tests were stated. Rice husks which are challenging to use in a conventional combustion chamber due to its relatively high ash content, which can lead to the formation of clinker and slag during combustion, have a great potential for high temperature pyrolysis. As it is one of the most important grains consumed in the world after wheat, its production is increasing day by day in Turkey and according to 2021 data, 1,000,000 tons are produced annually. Since the stalk/grain ratio is high (1/2), it is important to evaluate the stalks remaining on the field surface after the harvest as well as production. If it is not utilized, it creates a waste problem as it does not rot in the field until the next harvest due to the silicon it contains. With pyrolysis systems that can be installed near paddy fields, the waste problem can be solved and the energy can be transferred to synthesis gas and electricity, hydrogen, methane and liquid fuel production can be achieved. Another waste problem for all over the world, household sewage sludge, is being eliminated in Turkey with management methods that cannot go further than saving the day. If all the domestic treatment sludge collected and dewatered in centers throughout Turkey can be used in electricity production with the central pyrolysis systems to be installed, a total of 45 MW of electricity can be produced. As another waste problem, while pure and uncontaminated plastic and paper-derived wastes are recycled, contaminated plastics or composite wastes like labeling wastes are sent to landfills since incineration isn't effective due to their low melting point, and digestion isn't a common option yet. The annual amount of plastic and composite waste that cannot be recycled and is sent to disposal in the world is around 400 million tons. When these wastes with high energy content are sent to the incineration plant for disposal, they prevent organic substances from mixing with oxygen due to their melting temperatures, causing incomplete disposal and emission problems. When they are buried in regular landfills, they cannot support gas formation because their bacterial decay is very slow and the energy they contain remains underground. Converting these wastes into usable energy in an environmentally friendly and sustainable way using the pyrolysis method and using the remaining waste in agriculture will solve the management problem of non-recyclable plastic and composite wastes by producing high quality energy and syngas and sending the waste reduced to 1/50 of the volume of raw waste to landfill, even if it contains inorganics that are unsuitable for agriculture. Hazelnuts, which are the most grown hard-shelled fruit in the world after walnuts and almonds, are produced mostly in Turkey with 600-700 thousand tons per year, and the annual hazelnut shells produced from this production are around 100-150 thousand tons. Having similar shell structure, the total annual amount of apricot produced in the world is 4.1 million tons. The annual amount of apricots produced in Turkey is 850 thousand tons, and the apricot seed shells resulting from this production are around 100-130 thousand tons. In addition to their energy potential, hazelnut and apricot seed shells have the potential to be used as raw materials in the production of value-added chemicals such as activated carbon due to their low ash and high fixed carbon content. Activated carbon is lost when they are burned in boilers or stoves to use the energy it contains. While electrical energy and valuable synthesis gas are produced by the pyrolysis method, activated carbon is also obtained as a product, so it contains high potential. An extensive literature research was carried out in the second chapter. Tar-reducing processes in pyrolysis systems; mechanical removal, catalytic cracking, self-modification, and thermal cracking were mentioned. However, these methods capture tar from gas so the energy in tar is lost. Furthermore, the systems generate a lot of contaminated water, which induces another waste problem. Promising studies about catalytic cracking provide for converting tar into useful gas without wastewater generation. On the other hand, most of the catalysts become inactive by the deposit of carbon and moisture. Studies to generate effective catalysts with longer operation periods without regeneration continue. Other methods used to reduce tar are the self-modification of gasification systems and thermal cracking. Parameters of reactions like temperature, the residence time of solids and vapors, pressure, feed particle size and type of gasifier are effective on product ratios. Higher reaction temperature and vapor residence time result in lower condensable product and char and higher syngas. With the increase of homogeneous secondary tar reactions at temperatures higher than 650 °C; primary tar is converted into aromatics and smaller molecules and CO, CH4 and especially H2 concentrations in syngas increase. In the field of tar minimization through thermal cracking, in addition to conventional heated pyrolysis systems, developing continuous microwave pyrolysis systems is also promising. Besides having advantages; continuous microwave pyrolysis needs to be developed further in order to replace conventional heated reactors of commercial size due to reasons such as using only high-quality electrical energy, temperature measurement problems, and the inability to use reflective materials such as metals in the body of the reactor. Furthermore, at pyrolysis temperatures higher than 800 °C, the yield of H2 in the syngas from microwave pyrolysis was lower than in conventional pyrolysis due to the conversion of the hydrogen atoms to tar by side reactions such as hydrogen transfer reaction. In fluidised bed pyrolyzers, which also have high pyrolysis efficiencies, since the pyrolysis reaction occurs rapidly in the fluidized bed and the vapors resulting from the reaction are quickly removed from the hot region, there is no opportunity for secondary reactions to occur and tar rates are very high. For this reason, the fluidized bed pyrolysis system is mainly used in conditions where pyrolysis liquid production is desired. Conventional heated screw pyrolysis systems are one of the most preferred methods for medium and large-scale facilities, although they have some operational problems like the plugging risk, mechanical wear and tears of the screw and body, and poor mixing at the radial direction. Results of some relevant experiments with similar materials were mentioned. Experiments showed that with the increase of temperature and vapor residence time, tar yields were reduced, syngas yields and efficiencies were increased. The properties, pretreatments, characterization test methods and results of the supplied materials for experiments were explained in the third chapter. The rice straws used in the experiments were supplied baled from the İpsala region, and were shredded to pellet sizes with a 15 kW power and 100 kg/h capacity straw shredding machine at Namık Kemal University The paddy straw, which was pelletized without additives in a pelletizing machine with a vertical motor shaft and 6 mm hole diameter, was brought to ITU Sentek Laboratory in sacks and were crushed into 10-20 mm lengths and made ready to be used in the experiment. The sewage sludge supplied from Paşaköy Advanced Biological Treatment Facility, which is affiliated with İSKİ and produces 7,500 tons of sludge with 94% dry matter content every year, was dried from 30% dry matter content to 94% dry matter content with the on-site band dryer. The size of the samples is in the form of spheres with a diameter of approximately 2-12 mm. For composite waste, various separated label wastes and pellets containing cellulose and polymer-based wastes were supplied from Frimpeks Chemistry. In order for the samples and pellets brought to the laboratory to be mixed in the desired proportions, they were first chopped into small pieces in the shredder unit in the ITU Sentek Laboratory. Then, considering the waste rates in the label industry, they were blended in the proportions specified in Table 3.1 and pelletized in the 7.5 kW pelletizing machine in the ITU Sentek Laboratory. Hazelnut and apricot seed shells sent by AEROFEN Chemistry and collected from Giresun and Malatya provinces and surrounding areas, respectively, were sieved after comprehensive characterization studies were carried out and used separately in pyrolysis experiments in sizes between 2 - 15 mm. Thermogravimetric, elementel and calorific analysis were done for all materials. Then in order to design the dimensions and operating parameters and then evaluate the char conversion efficiency of the novel continuous reactor, batch pyrolysis experiments were performed in a 1 kg capacity rotating batch pyrolysis reactor. The horizontal batch reactor had a Ø140 mm diameter and 470 mm length. There was a perforated cover inside the reactor that largely prevented solid particles from going into the gas line. The reactor can be heated to 900 °C with a movable electric resistance chamber by PLC PID control. Gases were passed through the separator condenser unit and burned in the flare unit. Tars were collected in the catch-pot under the condenser. Syngas online analysis was provided with MRU SWG 200 Gas Analyzer. After the data was collected, the novel continuous pyrolysis system was designed and the parameters and calculation criteria used in the design are stated in section 4. The materials to be subjected to pyrolysis experiments in the laboratory were filled into a bunker placed in the material preparation room by opening the top cover. There was a robotic arm ventilation system to prevent possible odor and dust formation during filling. If any blending process was needed to be done on the material, the process was carried out in the bunker. Bunker capacity was determined as 50 kg. Although this amount was sufficient for the system to operate uninterruptedly for 5 - 10 hours, new material could be loaded into the bunker during operation for longer operations. The reactor system was designed to espose the resulting vapors to external heating along the line to enable secondary reactions to occur, and it was aimed to reduce the amount of tar and increase the amount of synthesis gas as much as possible. In order to eliminate inefficiencies that may occur as a result of intermittent operation, new material feeding and waste unloading operations were carried out continuously. In order to place the reactor in the resistance chamber appropriately and to check whether there is any damage or heterogeneous heating in the body and resistances after the reactions, the resistance chamber is assembled in two parts with a hinge and can be opened with hydraulic pistons when desired and the reactor inside can be controlled. A vacuum double valve system was used in the reactor feeding to ensure that no air, nitrogen or oxygen was taken in while feeding material into the interior of the reactor. The material loaded onto the screw was first loaded as a full section in order to maintain stability within the reactor, thus material was loaded linearly as long as the top of the screw remains full. The full spiral also provided a preheating process and prevented cold material from suddenly entering the reaction zone. In the reaction zone, a hollow helis that scraped the outer wall was used to prevent possible blockages and provide space for the produced gases. With this structure, material transfer was provided to the desired extent, the material was mixed axially and homogeneous heating was achieved, adhesion to the wall and agglomeration formations were prevented, and the ribbon screw was prevented from getting stuck and strained. The resistances surrounding the reactor body were heated in a PID controlled manner according to the temperatures determined through the automation system. The amount fed instantly was recorded cumulatively through the automation system, thus calculating how much heat was given at each moment of the reaction. Based on the reactor temperature of 900 °C, it was decided that Kanthal A1 resistance wires with a resistance temperature of 1300 °C were suitable for the application. Vapors and syngas leaving the reactor, was passed through a heated cyclone and a catalyst chamber to ensure the residence time was enough to achieve secondary reactions and tar minimization. Also dust was seperated from the gas without any condensation and fouling. After the catalytic chamber, which was operated without a catalyst at this study, vapors were condensed at the condenser and syngas was cleaned at the scrubber. Cleaned syngas was analyzed with MRU SWG 200 gaz analyzer and then combusted in the flare. At the fifth, the last chamber results and discussions were given. Char yields of continuous pyrolysis were similar to the sum of fixed carbon and ash yields in TGA results, which indicated that materials remained in the reactor for a sufficient time and were effectively mixed. The coexistence of materials at different reaction stages in the reactor enabled the pyrolysis reactions to take place in steam atmosphere coming from the drying side, resulting in 20% less char output in a shorter time compared to batch pyrolysis. The char yield of sewage sludge was higher than the others due to its high ash content. As intended, thanks to the high continuous pyrolysis temperature of 850 °C, the reactor shape, and heated chambers for the vapor with a 5-second residence time tar yields were measured lower than 1.65% for all five materials. Gas yields were in the range of 66 - 69% except for the high ash-contented sewage sludge. Although partial oscillations were observed in the gas composition after the gas output stabilized, it generally remained constant. It is thought that especially the concentration fluctuations in the rice husks and apricot kernel shell were caused by the irregular movement of the material in the reactor. The highest and lowest volumetric calorific value of gas was obtained at composite waste, and hazelnut shell pyrolysis by 20.37 MJ/m3 and 14.48 MJ/m3 respectively. Hydrogen volumetric yields in gas were between 31 – 35% and the highest value was obtained for hazelnut shells. During experiments energy consumptions on electric resistances were measured between 100.2 and 105.7 MJ, lowest in sewage sludge and highest in hazelnut shell. Heating chamber heat loss was measured as 88.1 MJ for test period by long term empty operation. Energy balance showed that ignoring hydrocarbons with two or more carbons resulted in 7 – 27 % energy deficit in HHV of syngas. The calculated HHV of CxHy in the experiment with composite waste was the highest one among others at 52.8 MJ which was 18. 9 % of total syngas energy, and the lowest one was in hazelnut shell pyrolysis as 11.5 MJ, 7% of total syngas energy. Since usability and control were taken into consideration in the pilot reactor design rather than highly efficient thermal insulation and sealing in the heating chambers, heat leaks were as high as 85% of total energy consumption. When moving from the experimental setup to the demo or commercial scale, energy consumptions will be much lower by overcoming the basic thermal runaways. Heat used in raw material heating and pyrolysis, which was named“total pyrolysis heat”and calculated by subtracting heat chambers heat loss from energy consumption in chambers, taken into account in determination of conversion efficiencies. Syngas energy efficiency was calculated as the ratio of total syngas HHV and sum of raw material HHV and total pyrolysis heat. Although the main target in the designed reactor is to minimize tar yield and produce as much gas product as possible, the energy in the produced char will also be evaluated through advanced processes. Char energy efficiency was calculated similarly to syngas efficiency, total char HHV divided by the sum of raw material HHV and total pyrolysis heat. Experiments have been carried out on the developed system for more than 400 days, and there has been no obstruction in the gas pipes or problem inside the reactor conveying and mixing mechanism that would prevent the operation. While working with products of different sizes and hardness, it has been observed that with the adaptive structure of the mixer screw, problems such as solid blockage, shaft breaking, structural deformation, gas compression, transport of unreacted material to the char discharge, more than 1% of the raw material staying in the reactor longer than desired were overcome. No sticking or blocking was observed in the gas pipeline, cyclone and catalyst chamber. Since most of the dust carried with gas was kept dry in the cyclone unit, there was no clogging problem either in the cyclone or in the shell and tube condenser. Based on a newly developed high-temperature continuous pyrolysis reactor with a modified ribbon screw, parameters targeted during design; product yields, gas energy conversion efficiency, gas higher heating values, hydrogen and methane production rates, fouling–blocking performance in the pipeline and mechanical performance in reactor conveying system were analyzed for five different materials. Novel conveying system was operated without sticking, fouling or blocking during semi-pilot scale continuous pyrolysis experiments. Due to enhanced mixing efficiency, char was minimized in residence time lower than 15 minutes. By increased vapor residence time in reactor and heated cyclone chamber, not only tar yields were decreased lower than 1.7 %, but also fouling and blocking in gas lines were prevented.
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