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Amonyak tesisinden enerji dengesi

Başlık çevirisi mevcut değil.

  1. Tez No: 55800
  2. Yazar: BÜLENT ECEVİT ERGÜN
  3. Danışmanlar: PROF.DR. HÜSNÜ ATAKÜL
  4. Tez Türü: Yüksek Lisans
  5. Konular: Kimya Mühendisliği, Chemical Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1996
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 71

Özet

ÖZET Enerjinin yoğun bir biçimde kullanıldığı amonyak tesislerinde mevcut olan enerji üretim, iletim ve kullanım sistemlerinin günümüz ekonomik koşullarına göre yeniden gözden geçirilmesi ve bu tesislerin artan enerji maliyetlerinin de göz önüne alınarak en verimli şekilde çalıştırılması, enerji girdilerinin azaltılması bu sanayi sektörünün hem yurt dışı rekabete karşı faaliyetini sürdürebilmesi nemde ülke çıkarları açısından zorunludur. Bu çalışmada, yukarıda belirtilen amaç doğrultusunda İstanbul Gübre Fabrikaları A.Ş.'ne ait olan Körfez-izmiî'de bulunan yapay gübre fabrikasının amonyak ünitesi proses koşullan ve enerji tüketimi incelenmiştir. Doğal gazdan amonyak üretim sürecinin proses kademeleri kükürt giderme, buharla dönüştürme, karbonoksitlerin giderilmesi, metanasyon ve amonyak sentezi olarak belirlendikten sonra her bir proses aşaması ayrı ayrı alınarak incelenmiştir. Daha sonra amonyak ünitesi bir bütün olarak göz önüne alınarak enerji dengesi kurulmuş ve bir ton amonyak üretmek için tüketilen enerji miktarı hesaplanmıştır. Hesaplanan değer dizayn değeri ile karşılaştırılarak dizayn koşullarından sapmanın neden olduğu maliyet artışları hesaplanmıştır. Bu maliyet artışları, amonyak üretiminde kullanılan girdi gazındaki hidrojen/azot oranının uygun olmamasından, buharla dönüştürme ünitesindeki buhar/karbon oranının dizayn değerinin üzerinde olmasından, amonyak sentez dönüştürücüsünde kullanılan katalizörün eski olmasından ve çeşitli hatlardaki buhar kayıplarından kaynaklanmaktadır. Bütün bu olumsuzluklara tesisin eski teknoloji kullanması neden olmaktadır. ıx

Özet (Çeviri)

ENERGY BALANCE OF AN AiWMONIA PLANT SUR/MARY Since 1973, the yearly energy statistics in the country are available. Evaluation of the past trends in fossil fuel productions showed some peak increases in certain years due to inauguration of new mines and power plants and the changes in supply-demand ratio. The average growth rates of the periods during which production rates have been stably increasing are included in the estimation of sustainability years. Technically and economically revcoverable reserves are also included in the estimation. Unless new fossil-fuel deposits are discovered or the possible reserves become feasibly extractable, indigenous fossil fuels have very limited lifetimes. The preceding broad review of the energy situation indicates that at present Turkey is heavily dependent on foreign energy, mostly in the form of oil, and will be more dependent in the future. In the coming two decades, energy imports in quantity are expected to increase approximately to five times today's imports. These high import growth rates could be significantly reduced if both energy production and conservation measures were effectively carried out. Energy production mesaures basically consist of any action to increase the use of indigenous fuels of the nation, so as to decrease the rates of energy imports. Implementation of new exploration programs, interfuei substitution in some sector, promotion of renewable energy uses wherever available and adoption of proper pricing and taxing policies are major energy production options for the country. Energy conservation mesaures attempt to improve the efficiency of energy use in a sector, activity or energy converting device. Thus, the value of energy output from a given amount of resources will increase by reducing energy waste. The energy literatüre is full of technical descriptions of energy conservation techniques should be made in accordance with the energy structure of a nation. As the energy situation varies widely among nations, so do the effective conservation measures in each sector.Industrial sector accounts for 31 % of the total national consumption. About 86 % of the total energy consumed by industry is in the form of fossil fuels; the balance is used as electricity. Most of the case studies on energy use by Turkish industry have been reviewed. Technical rehabilitation to achieve conservation is considered in four categories; 1. Process change 2. Process improvement through improved operations and controls 3. Improved insulation and heat recovery 4. Improved efficiency In this study the ammonia unit of the Fertilizer Plant of the Istanbul Fertilizer Company (IGSAS), is studied from the energy saving point of view. The plant starded production in 1977, is located in Kocaeli and has a capacity of 1100 tonnes ammonia per day and 1700 tonnes urea per day. Naphta had been used as starting raw material for ammonia synthesis up to 1988, then it was supplied by natural gas. Ammonia plants are, generally known for their intensive energy consumption. Therefore, any minor improvement in the process flowsheet or in the technology can save a large amount of energy. Almost all natural gas- based ammonia plants are based on overall process scheme introduced about 30 years ago, featuring desulfurization, primary and secondary reforming, two- step shift conversion, carbondioxide removal, methanation and synthesis (see Fig.1). Over the years this process scheme has been gradually improved by introduciton of new technology in the individual process steps, by overall optimization of the process lay-out, and by extensive integration between the process units and the steam and power system. The general discussion about ammonia technologies has focused strongly on the energy consumption. However, it is important to realize that the energy consumption is just one element in the production cost of ammonia. The required investment and the capacity utilization are also of importance and in most cases more important than the energy consumption. However, the energy consumption is very important factor in the comptetion between process licensors; this may partly be for historical reasons, dating back to the energy crises in the 1970's, partly because the energy consumption (at design conditions) is the most visible parameter in the early phases of a project, where the comptetion between technologies takes place. There is no simple relationship between energy efficiency and investment cost. It is often assumed that high energy efficiency must mean high investment, but this is not always true. In many cases improved efficiency can be obtained without increased investment or even at a reduction in investment. XINatural Gas -5». Desulphurization Primary and Secondary Reforming Two-step Shift Conversion ??^^ Carbon Dioxide Removal Methanation Ammonia Synthesis Refrigerated Storage -*- Product Figure 1. Process Steps in Ammonia Production The reason is simply that each time an extra investment is made or new technology is installed in one part of the plant in order to reduce energy consumption, savings will be obtained in other parts of the plant, because less energy has to be generated and/or removed, less gas has to be handled, etc. When more catalyst activity (larger volume or more active catalyst) is installed in order to increase the conversion across the synthesis converter, then the volume of recycle gas decreases, and the size and cost of heat exchangers, piping, etc. is reduced. When a larger heat transfer surfaces or improved heat transfer equipment is installed in order to improve the temperature aprroach, e.g. in the loop heat exchangers, then the size and cost of the refrigeration system are reduced. And when a purge gas recovery unit is installed in order to improve product yield, the consumption of make up gas decreases, and the size and cost of the complete front-end are correspondingly reduced. There is, of course, a limit to these effects, but it is quite diffucult to be very specific. The steam production in an ammonia plant may, for the same basic process lay- out, be varied within certain limits by adjusting various parameters. Some examples are: Introduction of combustion air preheat will reduce firing to the reformer and consume part of the heat available in the reformer flue gas, thus reducing the heat available for steam production. XIIincrease of methane content in the product gas from the reforming section will reduce the firing to the primary reformer, again reducing the amount of heat available in the reformer flue gas for steam production. Reduction of steam to carbon ratio at inlet reforming section will influence the steam in several ways. The firing to the reformer will be only marginally affected, since higher temperature is required to obtain the same conversion of methane. Less heat will be available in the product gas from the reforming section, due to the reduced flow, and the amount of low level heat released by condensation of excess water from process gas will be considerably reduced. This heat is used for boiler feed water preheating and for reboling in the carbondioxide removal unit, and low steam to carbon ratio is therefore most attractive in combination with carbondioxide removal process with low reboiler duty. The consumption of steam for process will be reduced, and the overall result of a reduction steam to carbon ratio will most often be an increase in the amount of steam available for other purposes. Increase of inert level in the synthesis loop makes the loop more efficient, and the size of the front end is correspondingly reduced. This will of course correspondingly reduce the amount of heat available for steam production. introduction of hydrogen recovery from the purge gas will have two effects. Firts of all, PGRU improves the efficiency in the same way as increased inert level, so that the size of -and therefore also steam generation in - the front end is reduced. Secondly, the recovery of hydrogen and nitrogen is normally different in PGR units, the recovery of hydrogen being the highest. This means that the synthesis gas before addition of recovered hydrogen has a H2/N2 ratio below 3. In order to produce this, the balance between primary and secondary reforming is changed, and firing to the reformer and thus the steam generation is changed. It should be noted that high inert level or installation of a PGRU will also change C02 production. Therefore, these options may not be available in ammonia/urea complexes where the size of front end is often determined by the required C02 production. The consumption figure obtained during the last four months is higher than the guaranteed figure of 8.71 Gkal/t NH3 due to several bottleneks. Mainly these are insufficiency of process air, high blow down rate of the boilers and a HP steam leakage at a safety valve. In detail the plant bottlenecks were determined through this study as: 1) According to the computer simulations the IGSAS plant is operated with a steam/carbon ratio of 3.65 For the moment this is done for safety reasons for the primary reformer catalyst. With the high steam/carbon ratio more heat absorbed in the primary reformer and therefore more fuel is consumed. xiii2) According to laboratory analysis the plant was operated with a hydrogen/nitrogen ratio around 2.957 while the design and optimum ratio is between 2.6-2.8. 3) In the C02 removal unit there is a high loss of the DEA, mainly caused by the condendsate treatment. 4) By extracting the purge gas, after the additon of make up gas, valuable hydrogen is extracted from synthesis loop. 5) A major minus for efficiency of the plant is direct loss of HP-steam through a leakage at a safety valve. This leakage leads to a increase in energy consumption. xiv

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