تانک ازت

تانک ازت که با نام های دیگر (تانک ازت مایع ، فلاسک ازت مایع ، فلاسک نیتروژن ، مخزن ازت ، مخزن نیتروژن و کانتینر ازت مایع) نیز یاد می شود

تانک ازت محفظه ای برای نگهداری ازت است ؛ از ازت مایع در موارد بسیاری می توان استفاده کرد . از آن به صورت متداولی در محیط های آزمایشگاهی و برودت شناسی استفاده می شود . افراد زیادی از آن حتی برای مصرف شخصی به عنوان یک یخچال استفاده می کنند . یک تانک ازت مایع برای نگه داشتن هر چیزی به صورت منجمد برای یک مدت طولانی ، یا به طور کلی به عنوان یک انتقال دهنده برای ازت مایع ، می تواند بسیار مفید باشد . شما هم چنین می توانید انتظار دیدن تانک ازت مایع در بیمارستان ها را داشته باشید . در حقیقت ، بیمارستان ها از آن ها اغلب اوقات استفاده می کنند . ازت مایع یک نگه دارنده ی برودتی برای بسیاری از مواد انسانی نظیر خون و نطفه است . هر بیمارستانی از تانک ازت مایع برای ذخیره سازی تخمک ها ، نطفه ، خون و حتی اعضای بدنی اهدا شده ، استفاده می کند . در حقیقت ، بیمارستان ممکن است بزرگترین مصرف کننده ی تانک های ازت مایع باشند .

علاوه بر یک تانک ازت مایع ، شما هم چنین می توانید خودروی ازت مایع و فریزر های ازت مایع را پیدا کنید . یک خودروی ازت مایع به سادگی خودرویی است که با مصرف ازت مایع کار می کند . در نتیجه ، ازت مایع به عنوان یک منبع انرژی قابل تجدید در نظر گرفته می شود در حالی که سوخت های فسیلی محدود هستند . خودرو های ازت مایع ممکن است چیزی باشند که در آینده به چشم بخورند. شما هم چنین می توانید فریزر های ازت مایع را در بیمارستان ها نیز ببینید . آن ها معمولا به همان منظوری به کار گرفته می شوند که از تانک ازت مایع استفاده می شود ، ولی دوباره برداشتن محتوا از آن ها آسان تر است . یک تانک ازت مایع ممکن است قفل هایی بر روی خود داشته باشد که بستن و باز کردن آن ها همیشه سخت باشد ، ولی انتقال آن ها آسان تر است چون اکثر آن ها به چرخ هایی مجهز می باشند . همان طور که اشاره شد ، یک فریزر ازت مایع که با نام فریزر آزمایشگاهی نیز شناخته می شود به منظور نگه داشتن مواد مهم در یک دمای ثابت است . گاهی اوقات ، در بیمارستان ها ، شما شاهد ترکیبی از فریزر ازت مایع و تانک ازت مایع هستید . شما متوجه خواهید شد که افراد زیادی مواد خود را در تانک های بسیار کوچکی قرار می دهند تا بتوانند در یک فریزر به صورت مرتب شده قرار دهند .

برچسب‌ها: تانک ازت, تانک ازت چیست, تانک ازت مایع, فلاسک ازت مایع

مولدهای اکسیژن و نیتروژن به روش سرمایش (Cryogenic) جداسازی هوا به روش کرایوژنیک یا سرمایشی، فرآیندی است که به جهت تولید اکسیژن و نیتروژن خالص به صورت گازی و یا توسط فشرده سازی داخلی به صورت اکسیژن، نیتروژن و آرگون مایع به کار برده می شود.مراحل روش سرمایشی عبارتند از: 1-فشرده کردن هوای محیط توسط توربو کمپرسور چند مرحله ای که مجهز به خنک کن های داخلی اند. این عملیات در فشار 6 بار انجام میشود. زدودن ذرات گرد و غبار توسط یک فیلتر هوا در ورودی کمپرسور انجام می شود. 2-سرد کردن و خالص سازی هوا:خنک کردن فرآیندی است که به صورت مستقیم توسط آبی که در تماس با کولر می باشد انجام می شود. خنک سازی کولینگ واترها در یک خنک کن تبخیری که در آن از جریان جبرانی نیتروژن استفاده می شود انجام می پذیرد.زدودن دی اکسید کربن، بخار آب و هیدروکربن ها از هوا در فواصل معین بارگذاری و احیا توسط جاذب غربال مولکولی انجام می شود. 3-انتقال حرارت در درجه پایین: سرمایش هوای مورد نظر در مبدل های گرمایی به زیر دمای میعان و توسط گاز نیتروژن اضافی حاصل از جریان سردساز و به صورت ناهمسو انجام می پذیرد. 4-سرد و فشرده شده سازی محصولات داخلی: فشرده کردن بیشتر جریان هوا توسط بوسترها انجام می شود سپس عملیات انبساط و خنک کردن جریان هوای تقویت شده در توربین های انبساط انجام می شود. انبساط و میعان جریان جانبی هوای تقویت شده در جدا کننده های مایع انجام می شود.فرآیند تبخیر و گرم کردن اکسیژن و نیتروژن پمپ شده تا دمای محیط، در یک مبدل گرمایی فشار بالا انجام می شود. 5-سرد کردن کرایوژنیک هوا: جداسازی اولیه هوای میعان یافته و سرد شده به ستون تقطیر انتقال می یابد و جریان غنی از اکسیژن مایع پایین ستون و جریان غنی از گاز اکسیژن خالص از بالای ستون جمع آوری می شود. مایع کردن گاز نیتروژن خالص در کندانسور انجام می شود حال آن که اکسیژن خالص در انتهای ستون فشار پایین و از ریبویلر جمع آوری می شود. نیتروژن مایع یک جریان برگشتی برای ستون فشار و پس از فوق سرد شدن برای ستون فشار پایین فراهم می آورد. جداسازی مجدد و بیشتر در ستون فشار پایین انجام شده و اکسیژن خالص از پایین ستون و نیتروژن خالص از بالای ستون تقطیر خارج می شود. 6-سرد سازی کرایوژنیک آرگون:گاز غنی از آرگون از ستون فشار پایین از طریق فرایند جداسازی در ستون آرگون خالص به گاز آرگون عاری از اکسیژن منتقل می شود. اکسیژن مایع حاصل از ستون آرگون به ستون فشار پایین منتقل شده و زدودن نیتروژن مایع هم در ستون آرگون انجام می گیرد.

برچسب‌ها: cryogenicpng برچسب ها, مولدهای اکسیژن به روش سرمایشی, مولدهای نیتروژن به روش سرمایشی, مولدهای اکسیژن به روش cryogenic

The idea that the air that we breathe could turn into a liquid is counterintuitive to say the least, but scientists have known how to liquefy the constituents of air for well over a century, and the industrial gases industry now produces thousands of tonnes of liquid nitrogen and liquid oxygen every day. However, these gases need not be separated when liquefied, in which case the result is liquid air. A number of technologies are now being developed to exploit liquid air – or liquid nitrogen, its main constituent - as an energy vector.

Air can be turned into a liquid by cooling it to around -196C using standard industrial equipment. 700 litres of ambient air becomes about 1 litre of liquid air, which can then be stored in an unpressurised insulated vessel. When heat is reintroduced to liquid air it boils and turns back into a gas, expanding 700 times in volume. This expansion can be used to drive a piston engine or turbine to do useful work. The main potential applications are in electricity storage, transport and the recovery of waste heat.

Since the boiling point of liquid air (-196C) is far below ambient temperatures, the environment can provide all the heat needed to make liquid air re-gasify. However, the low boiling point also means the expansion process can be boosted by the addition of low grade waste heat (up to +100C), which other technologies would find difficult to exploit and which significantly improves the energy return. There are myriad sources of low grade waste heat throughout the economy (see chapter 5).

The industrial gases industry has been producing liquid nitrogen and liquid oxygen – the main components of liquid air - for over a century. These cryogens have a wide range of applications including steel-making, food processing, medicine and superconducting technologies. Since oxygen and nitrogen liquefy at similar temperatures, and since there is four times more nitrogen than oxygen in the atmosphere but much less demand for it commercially, the industry has substantial spare nitrogen production capacity. The thermo-physical properties of liquid nitrogen and liquid air are similar, so a cryogenic energy vector could be provided by either.

There have been several attempts to exploit liquid air or liquid nitrogen as an energy vector over the past century without commercial success. However, technological advances and market evolution in the early years of this century appear to have made it a practical and economic possibility worth considering again. In this chapter we describe how liquid nitrogen and liquid air are produced, and introduce the new technologies being developed to exploit them as energy vectors.

 

Attempts to develop liquid air as an energy vector date back to 1900, when the Tripler Liquid Air Company was formed in the US to develop a liquid air car that briefly competed with the steam and electric vehicles of the day.¹ But early liquid air vehicles required bulky and inefficient external heat exchangers, and soon the internal combustion engine came to dominate road transport, so it was not until the second half of the twentieth century that interest in cryogenic engines revived.

In the 1960s, self-powered cryogenic pumping systems² were explored as an alternative to electric pumps for fuel delivery in rockets. However, this was at the height of the space race and cold war, so very little information is available. With the arrival of the oil crises in the 1970s interest in cryogenic cars returned, and a number of patents were filed, although few, if any, vehicles were actually built.³ There was also interest in developing liquid air as a grid-scale energy store, evidenced by a paper presented to a conference of the Institution of Mechanical Engineers in 1978.⁴

The 1980s saw the first recorded work on hybrid or dual-fuel cryogenic vehicles, where fossil fuels were typically used to raise the temperature of a cryogenic working fluid to increase its energy density. The combination of cryogenic engine and internal combustion engine was found to produce synergistic increases in efficiency, which in one case delivered a 50% greater range than using each fuel on its own.⁵

Another engine proposed in 1984 with the help of US Department of Energy funding⁶ worked by superheating liquid nitrogen to very high temperatures in a furnace powered by any fossil fuel, before expansion in the cylinder. The fuel consumption of this configuration was 4.2 miles per gallon of liquid nitrogen and 132 mpg of petrol. At 1984 prices, projected driving costs were comparable to a similar specification petrol car. Systems using LNG as the fuel were also proposed.

In the early 1990s, the California Air Resources Board’s Zero Emission Vehicle mandate created significant interest in alternative engine technologies. Recognising the limitations of electric vehicle concepts of the time, the Universities of Washington and North Texas began research programmes into cryogenic engines for transport, and built some demonstration units capable of achieving speeds of a few miles per hour.⁷

A number of utility-scale applications were also developed and tested, including one from Mitsubishi called LASE – Liquid Air Storage Energy System.⁸ The design involved producing liquid air during off-peak periods and then pressurising it to supply high pressure gas to the air inlet valve of a gas turbine to boost its output.

After a century of faltering attempts to exploit liquid air, what appears to have been a significant breakthrough came in 2001, when the British inventor Peter Dearman developed and patented the Dearman Engine. Mr Dearman’s key insight was that liquid air could be vaporised inside the engine cylinder using heat supplied by a thermal fluid mixture such as water and antifreeze, eliminating the need for the bulky and inefficient external heat exchangers of traditional cryogenic engines. This insight allowed Dearman to make simple modifications to a small car and run it on liquid nitrogen at speeds of more than 30mph.⁹

By contrast, in 2005 the Ukranian Kharkov National Automobile and HighwayUniversitydeveloped a two person lightweight road car whose design continued to rely on an ambient heat exchanger, and this achieved just 10 kph for 42 minutes on 22 kg of liquid nitrogen.¹⁰

After buying the rights to the Dearman Engine, Highview Power Storage went on to develop the grid scale energy storage system described below. In 2006, working with scientists at the University of Leeds, Highview developed a series of efficiency enhancements to the liquid air cycle by integrating the production and expansion processes to make use of waste heat and cold, so making the concept economically viable. In 2010, Highview spun off the Dearman Engine Company to develop a cryogenic engine for transport applications. Today a number of companies around the world are investigating the use of liquid air as an energy vector for transport and grid scale applications.

 

Air is made up of nitrogen (78%), oxygen (21%) and argon (1%), and these components can be separated because they liquefy/boil at different temperatures: nitrogen at -196°C, oxygen at -183°C and argon at -186°C. This is done using an Air Separation Unit (ASU).

First the air must be cleaned through a dust filter, and compressed to a pressure of about 6 bar (Figure 2.1, step 1). The compressed air is then cooled down to a temperature of about 15°C (2). Then water and CO2, which would otherwise freeze and block pipes in the ASU, are removed using a molecular sieve in a process known as adsorption (3).

The cleaned air is then cooled down to close to liquefaction temperatures by repeatedly compressing and expanding the gas and passing it through a heat exchanger, much like a domestic refrigerator (4). Most of the energy needed for air separation is consumed by this part of the ASU.

The extremely cold air is now separated into its components in two distillation columns (5), in which gas moves to the top and liquid falls to the bottom. In the first, medium pressure column, air is separated into nitrogen gas and an oxygen enriched liquid containing 30% oxygen. In the second, low pressure column, the full separation of oxygen and nitrogen is achieved, and both are available in liquid or gaseous form (6). These products are typically delivered to customers as compressed gases by pipeline or cylinder, or as liquids by road tanker.

 

 

Figure 2.1: Air Separation Unit. Source: Messer

 

The process inevitably produces excess nitrogen, because there is four times as much nitrogen as oxygen in the atmosphere but much less demand for it commercially. Some of the excess nitrogen is recycled to cool incoming air, so raising the energy efficiency of the ASU, but much is vented harmlessly to the atmosphere. Spiritus Consulting estimates excess nitrogen production capacity in the UK at 8,500 tonnes per day (tpd) (see chapter 6). Since this excess nitrogen is in gaseous form, exploiting it as an energy vector would require the construction of additional liquefiers at existing industrial gas production sites.

Air can be liquefied without separating the oxygen and nitrogen using only the ‘front end’ of an ASU – essentially steps 1-4 above. Air is cleaned, compressed and water and CO₂ removed, and the air then liquefied using a compressor, turbines and a heat exchanger (a ‘liquefier’). There is no need for the distillation columns, and the liquid air can then be stored in tanks similar to those used for liquid oxygen or nitrogen. A diagram of this simpler process is shown in Figure 2.2.

 

Figure 2.2: Air liquefier

 

The amount of energy required to produce a tonne of oxygen or nitrogen using ‘best available technology’ is shown in Table 2.1.¹¹ According to Messer, the German industrial gas company, of the 549kWh required to produce a tonne of liquid nitrogen, about 20% is consumed in the separation process. Producing a tonne of liquid air therefore consumes about 439kWh.

 

Table 2.1: The energy consumption of oxygen and nitrogen production.  

Source: EIGA¹²

 

Liquefied gases can be stored in two types of tank: smaller vacuum insulated, and larger flat-bottomed. The advantage of vacuum insulated tanks is that they can be operated at any pressure required, depending on the construction material. They can be economically produced up to a size of 300m³. Any tank larger than 500m³ will be flat bottomed, insulated with the volcanic material perlite, and will operate at near-atmospheric pressure – typically 30-100mbar.

Because the temperature outside the tank is typically ~200C warmer than inside, heat leaks inwards and causes some of the liquid to boil off. The boil-off rate for both vacuum insulated and flat-bottomed tanks is about 0.1-0.2% per day – although the rate for larger tanks can be as low as 0.07%. Because nitrogen boils at a lower temperature than oxygen, a tank of liquid air may gradually become oxygen enriched. As we discuss in chapter 8, this is a hazard that must be managed, since liquid oxygen is highly reactive.

 

A large scale, long duration energy storage system based on the liquid air cycle has recently been developed by Highview Power Storage and demonstrated at a 300kW pilot plant in Slough. The plant is hosted by SSE (Scottish & Southern Energy) next to its biomass power station, and was partly funded by the Department of Energy and Climate Change (DECC). The pilot plant has been successfully tested against standards set by National Grid and other international electricity system operators (UK STOR and TRIAD markets, US PJM market). A 10MW commercial demonstration plant is now planned, and the company predicts efficiencies and costs will improve at progressively larger scales. The system is built from components already widely used in the industrial gases and electricity generating industries, but combined in a novel form that the company calls a Cryo Energy System, and describes more generically as Liquid Air Energy Storage.

The system consists of three main elements: charging, storage and power recovery (see figures 2.3 and 2.4). First, grid electricity is used to power an air liquefaction plant (the front end of an industrial gas separation unit) to refrigerate air to its liquid state. The liquid is then stored in an insulated tank at low pressure*, which functions as the energy store. When power is required, liquid air is drawn from the tank and pumped to high pressure and into a heat exchanger, where ambient and low grade waste heat turns the cryogen into a high pressure gas, which is then used to drive a turbine and generator to deliver electricity back to the grid.

Cryogenic tanks that hold less than 100 tonnes are typically held at

 

Figure 2.3: Schematic of a Liquid Air Energy Storage system. Source: Highview Power Storage

 

The efficiency of the process is increased by exploiting both waste heat and waste cold. The use of low grade waste heat during expansion generates additional power that improves the overall round trip efficiency of the cycle; the cycle’s maximum efficiency is determined by the highest and lowest temperatures, so raising the higher temperature with waste heat increases the available work. At Slough, waste heat at around 60C is sourced from the biomass power station next door. Performance data shows this heat is converted into power at an efficiency of 50-60%.¹³

 

 

Figure 2.4: the Highview Power Storage pilot plant in Slough. Source: Highview Power Storage

 

BOX 2.1: Liquid Air Energy Storage process 

 

Figure 2.5: Schematic of a Liquid Air Energy Storage device. Source: Highview Power Storage. 

 

The schematic separates the process into three sections: charging (grey); storage (green); and discharge or power recover (red). The air is first compressed (1) and passed through a filter to remove water and carbon dioxide, that would otherwise freeze and block the process. The air is compressed in a recycle air compressor (2) and then cooled in a series of heat exchangers, referred to as a cold box (3). The now very cold air is expanded where most of the flow condenses to liquid (4). The part of the flow that is not condensed returns through the cold box to cool the main high pressure flow. Part of the flow from the recycle compressor is diverted to a separate channel in the heat exchanger where it is cooled and expanded through a turbine (5). This achieves more efficient cooling and reduces the energy required to liquefy the air. The liquid air is then stored in an insulated tank (6). The discharge process follows the Rankine cycle. The thermal energy required to heat the cold liquid after compression is captured and stored in a thermal store (7) after the liquid pump (8). The resulting warm high pressure gas is expanded through a series of turbines (9) to generate electricity. 

The process as described could achieve an efficiency of around 25%. The efficiency is greatly increased by storing and recycling the thermal energy released during the power recovery process, more than doubling the process efficiency to 50-60%. This is achieved by capturing the cold thermal energy released during the power recovery process in a thermal store, typically a bed of gravel. The thermal energy stored in the gravel bed is then used to improve the efficiency of the liquefaction process by circulating dry air through the cold box and thermal store, transferring the thermal energy from the store to the cold box. The result of this ‘cold recycle’ is that less air is recycled round the process through the expansion turbines (5) and more of the air is turned to liquid during the expansion process at the separator (4), reducing the energy cost of manufacturing a specific quantity of liquid air. 

 

The turbine exhaust gas is also recycled as part of the process and its residual heat removed to help drive the evaporation of the cryogen. This then produces a very cold gas stream, the cold content of which is stored in a proprietary high-grade cold store, and used to pre-cool incoming air when liquefaction next takes place, so further raising the efficiency of the plant. The process is described in more detail in Box 2.1.

The pilot plant was fully commissioned in July 2011 and has been tested for cold recycle, reliability, response and heat to power performance. In testing against National Grid STOR criteria, the pilot plant proved 95% reliable, considered high for a pilot plant, and in testing against the US PJM self testing protocol, the plant was 99.8% compliant – against a pass mark of 75% - as reviewed by the PJM assessors. The plant was able to reach desired output within 2½ minutes, meaning that at larger scale the technology is a potential candidate for the fast reserve market as well as STOR. A full technical description of the Cryo Energy System provided by the company forms Appendix 1.

The pilot plant was built from standard components that are widely used in the industrial gases and power generation industries. The company is now planning a 10MW/40MWh Commercial Demonstration Plant with ~300 t/day liquefaction plant and a high grade cold store on the same basis. All of the main components of the system are more efficient at commercial scale, and the company has calculated this will raise round-trip efficiency to 60%.¹⁴ Other companies are also reported to be investigating the opportunity of liquid air storage, including Praxair, Air Products and Expansion Energy in the US, but there is no news to date of any hardware deployed.

 

The Cryo Energy System is a fully integrated electricity storage system in which liquid air is produced and consumed on the same site. However, liquid air could also be produced in one place and used to generate electricity in another. The liquid would be transported between sites in the same way industrial gas companies distribute liquid oxygen and nitrogen today - typically by road tanker (Figure 2.6). This might make sense for applications where the generator is too small, or used too infrequently, to justify the cost of building an on-site liquefier. It could also make use of an estimated 8,500 tonne per day surplus of nitrogen production capacity in the UK (chapter 6). 

Highview Power Storage has developed a generation-only device to fulfil this function called the Cryogenset. It is essentially the same as the Cryo Energy System described above but without the liquefier, and whereas the storage system would scale from 10MW to several 100MW, the Cryogenset is designed for 3-10MW.

The Cryogenset is intended eventually to compete with diesel generators and Open Cycle Gas Turbines (OCGT) in their roles as corporate emergency back-up power and grid peaking plant that typically generate for less than 100 hours per year (chapter 3). It is estimated that UK companies have diesel generators with a total capacity of around 15GW, of which about 2.5GW are in units of 1MW or larger. National Grid currently contracts 493MW of diesel generation and 346MW of OCGT capacity as part of its Short Term Operating Reserve.¹⁵ The Cryogenset shares many characteristics of diesel gensets and OCGT, such as low capital cost and relatively fast start up times (less than 15 minutes), but with the added benefit of lower carbon emissions, since liquid air generated from off-peak electricity is likely to be less carbon intensive than diesel or gas when burned in inefficient open cycle plants (chapter 10).

 

 

Figure 2.6: Schematic of a Cryogenset. Source: Highview Power Storage

 

 

The Dearman Engine Company is developing a cryogenic engine that operates through the vaporisation and expansion of liquid air or liquid nitrogen. Ambient or low grade waste heat is used as an energy source with the cryogen providing both the working fluid and heat sink. Heat is introduced to the cryogenic fluid through direct contact heat exchange with a heat exchange fluid (HEF) inside the engine.

Figure 2.7 shows an overview of key parts of the Dearman Engine process. On the return stroke a warm heat exchange fluid flows into the cylinder filling nearly all of the dead volume. Just after top-dead centre the liquid air or nitrogen is injected directly into the heat exchange fluid. There is a large surface area and temperature differential and this causes the cryogenic fluid to boil very rapidly.

As the fluid turns into a gas it expands, and this expansion process drives the piston down the cylinder for the power stroke. During this process, the heat exchange fluid keeps giving up heat to the expanding gas ensuring a nearly isothermal expansion – the gas expands yet the temperature remains relatively constant.

 

 

Figure 2.7: The Dearman cycle. Source: Dearman Engine Company

 

At bottom dead centre an exhaust valve opens allowing the mixture of gas and heat exchange fluid to exit the cylinder. The heat exchange fluid is recovered from the exhaust stream and reheated whilst the air or nitrogen gas is exhausted to the environment.

While cryogenic expansion engines are not new, previous incarnations have worked on an open Rankine cycle – similar to a traditional steam engine but operating across a different temperature range. Under this arrangement the cryogenic fluid is pumped to operating pressure and vaporised through a heat exchanger before expansion in the engine cylinder.

A number of drawbacks exist with this arrangement when applied to mobile applications, since the heat exchanger must be large to cope with the heat transfer rates, and heavy to withstand the high pressure. Since little heat is added to the gas during the expansion phase in the engine cylinder, it cools while expanding (near adiabatic expansion) so reducing the work output.

The novelty of the Dearman Engine lies in the use of a heat exchange fluid (HEF) to facilitate extremely rapid rates of heat transfer within the engine. This allows injection of the liquid cryogen directly into the engine cylinder where heat transfer occurs via direct contact mixing with the HEF. The heat transfer on injection generates very rapid pressurisation in the engine cylinder. Direct contact heat transfer continues throughout the expansion stroke giving rise to a more efficient near-isothermal expansion.

The inventive step is covered by a patent covering the European Patent Office (EPO), US and Japanese territories. In December 2011 the company filed a subsequent application covering insights derived from its engine testing experience.

The specific work available from an expansion over a variety of pressures is shown in Figure 2.8 for both adiabatic expansion, where no heat is added and the gas inevitably cools as it expands, and isothermal expansion, where heat is added during expansion to maintain a constant temperature, so increasing the work output. The dashed lines indicate the specific work from the expansion net of pumping work.

 

 

Figure 2.8: Specific work from the expansion of liquid air

 

The benefit of the pressurisation process taking place in the cylinder is to reduce the amount of pumping work required to reach a given peak cylinder pressure, meaning that the likely specific work from a kilogramme of liquid nitrogen is between the dashed and solid lines. The benefit of having a heat source present during the expansion stroke - the core Dearman Engine invention - is demonstrated by the difference in specific work availability between the adiabatic and isothermal processes. Taking the benefits of in-cylinder pressurisation and heat transfer together, the likely specific work from a kilogramme of liquid nitrogen is between the dashed and solid red lines.

The engine has two unique capabilities within the zero-emission engine space:

Heat to power

The Dearman Engine power cycle has a bottom temperature of about -196C and peak cycle temperature of ambient, meaning even relatively low grade heat can increase the peak cycle temperature and be converted into additional work at very high conversion efficiencies. The Dearman Engine can be deployed as a high yield thermal energy recovery system that could convert heat from the exhaust or coolant systems of an internal combustion engine into shaft power at conversion efficiencies of up to 50%. This would have the advantages of:

• reducing or eliminating the loads associated with heat rejection on the IC engine;

• enabling the IC engine to be downsized;

• displacing a material portion of transport related emissions into an energy vector (liquid air) that can be produced from renewable sources.

Initial comparison suggests that liquid air can be profitably substituted for on-highway hydrocarbons, so there is a fuel cost saving too (see chapter 6).

Fuel cells also give off large amounts of heat, so in future the Dearman engine could be used to raise the efficiency of vehicles powered by hydrogen (chapter 5) as well as fossil fuels.

Cooling

The engine absorbs significant quantities of heat during its operation and so can be viewed as a heat sink or cooling source. If there is a requirement for a heat sink or cooling source (eg air conditioning or refrigeration) then a Dearman Engine can simultaneously displace cooling loads and generate shaft power. The engine absorbs approximately twice as much heat as shaft power generated.

 

The auto engineering consultancy Ricardo is conducting engine development for the Dearman Engine Company, and a fully characterised bench prototype is expected to be completed by the end of 2013. However, Ricardo has also proposed another engine concept to exploit the potential benefits of liquid nitrogen. Whereas the Dearman engine uses liquid air as fuel, Ricardo’s engine would run on petrol or diesel but incorporate a quantity of cryogenic gas into the cycle to make it significantly more efficient. The Ricardo design is based on advances in static electricity generation technology.

In power generation, a Combined Cycle Gas Turbine (CCGT) is extremely efficient in spite of its low compression ratio. This is because the temperature difference between the compressed inlet air (Figure 2.9 position 2) and the exhaust gas (position 5) is big enough to allow significant heat transfer, meaning that heat from the exhaust can be used to raise the temperature of the compressed air through a heat exchanger or ‘recuperator’ before combustion. This reduces the amount of fuel required to achieve the same output.

 

 

Figure 2.9: Combined Cycle Gas Turbine

 

By contrast, the ICE derives its efficiency from having a high compression ratio, and this means the temperature of the compressed air is too close to that of the exhaust to allow effective heat transfer; waste heat from the exhaust cannot be recovered. In addition, most ICE designs compress and expand the air in the same cylinder, making it impractical to introduce a recuperator into the system.

This problem can be overcome using a split cycle engine design similar to the Isoengine concept first developed by Ricardo in the 1990s and the Scuderi engine today. In such designs, compression takes place in one cylinder and expansion in another, which is similar in concept to a gas turbine. However, to make the split cycle thermodynamically efficient requires isothermal compression, in which the air remains at a relatively constant temperature despite being compressed. The temperature-entropy diagram in Figure 2.10 shows how isothermal compression allows the temperature difference between the compressed intake air and the exhaust gas to be maximised, so creating an opportunity for waste heat recovery.

 

Figure 2.10: Recuperated diesel cycle with high compression ratio and isothermal compression. Source: Ricardo

 

Isothermal compression can be achieved by spraying a fluid into the compression chamber to absorb heat from the gas being compressed, and this approach has been tested in a 3MW power generation demonstrator using water. However, although this produced a large demonstrable gain, raising gas to electricity conversion efficiency to 59%, it also required large quantities of water because of the small temperature difference between it and the air being compressed, along with complex and expensive water management equipment.

The Ricardo split cycle invention replaces water with liquid nitrogen which is far colder at about -200C, meaning that far smaller volumes are required. In addition, once vaporised during compression the nitrogen can then pass straight through the combustor and be exhausted to the atmosphere. As a result, the system can be made far more compact and suitable for vehicle engines.

Detailed modelling of this approach under-taken through the TSB ‘CoolR’ programme has suggested an efficiency of more than 60%. As a result, a modest onboard tank of liquid nitrogen would extend the range of the vehicle by increasing the efficiency of the primary engine. Liquid nitrogen could also be produced by an onboard liquefier driven by the engine and boosted by regenerative braking.

 

Technologies that use liquid air as an energy vector exploit its thermo-physical properties - its expansion between liquid and gaseous phases and/or its ability to absorb heat. Air and nitrogen have relatively similar thermo-physical properties and so most technologies under consideration (except the Ricardo split-cycle engine) could use either liquid nitrogen or liquid air. The choice is likely to be driven by existing supply, economics, infrastructure, safety and application-specific factors.

One major advantage of nitrogen is the industry has a substantial surplus of production capacity both in the UK and globally (chapter 6). This arises because there is four times more nitrogen than oxygen in the atmosphere but much less demand for it commercially. Spiritus Consulting estimates the surplus amounts to about 8,500 tonnes of nitrogen gas per day, which currently is simply vented to the atmosphere. To turn this into a cryogenic energy vector would require investment in additional liquefiers. If that were done, this surplus could absorb 4.6GWh¹⁶ of ‘wrong time’ wind generation and, at 60% round trip efficiency, deliver 2.8GWh back to the grid, enough to power the equivalent of 310,000 households.¹⁷ Alternatively it could potentially fuel the equivalent of 6.5 million car kilometers daily.¹⁸ Since the marginal cost of exploiting this waste product is low (chapter 6), it is likely that many early applications of ‘liquid air’ would in fact run on liquid nitrogen.

Once the nitrogen surplus has been exhausted, liquid air would have an economic advantage since its production requires less equipment and less energy than liquid nitrogen and should therefore be cheaper. A wide range of air liquefiers is already available commercially, ranging from small-scale units producing 2,000 litres per day, made by companies such as Stirling Cryogenics of the Netherlands¹⁹, to industrial plants of about 30 tonnes per day, such as the Chinese unit installed by Highview Power Storage at its pilot plant in Slough. There is no barrier to scaling these liquefiers up to units of several thousand tonnes per day as they are typically based on industry standard designs for nitrogen liquefiers which are already available at these scales. Once investment in new plant is required to supply cryogenic energy vectors, these simpler and cheaper systems will have a cost advantage, and liquid air may therefore be preferred over liquid nitrogen. 

One disadvantage of liquid nitrogen compared to liquid air is that its exhaust is not breathable since it contains no oxygen (safety issues are covered in detail in chapter 9). This would preclude its use in enclosed spaces such as mines or warehouses without appropriate ventilation and oxygen monitoring equipment – the same precautions employed for fossil fuel powered engines. In these circumstances liquid air would be the preferred option, since the exhaust is breathable. Both liquid air and liquid nitrogen would provide free cooling from cold exhaust.

The disadvantage of liquid air is the potential for oxygen enrichment, which is a potentially serious hazard, although one that has been safely managed by the industrial gases industry for decades. Liquid air can become oxygen-enriched because nitrogen has a lower boiling point than oxygen, and so can evaporate more quickly in some circumstances, raising the oxygen concentration to higher than that found in the atmosphere. As we discuss in chapter 9, this hazard can be managed using equipment to prevent such enrichment, monitoring and safety procedures.

In the case of liquid air that is produced and consumed over short periods or hours or days – a grid balancing unit operating in the STOR market, for example - there is no danger of enrichment in any event.²⁰ But for strategic energy storage over weeks or even months, the risk would be higher. In this case the risk could either be managed as described earlier, or eliminated entirely by using liquid nitrogen rather than liquid air (chapter 9).

Neither liquid air nor liquid nitrogen emit CO₂ at the point of use, and both can be low carbon energy vectors depending on the energy source used to produce them. Liquid nitrogen is already typically generated during off-peak hours when electricity prices and carbon intensity are lower. In future, production of liquid nitrogen and liquid air could be ‘wind-twinned’ – concentrated in periods when the proportion of wind generation is highest.

Nor do they produce the nitrous oxide (NO_X), sulphur dioxide (SO_X) or particulates (PM10) associated with diesel generators, so cryogenic backup generators could have a beneficial impact on air quality in urban areas.

On balance it seems likely that early applications will exploit the nitrogen surplus except where there are specific reasons to choose liquid air, and that over time, as new production capacity is built, the advantages of liquid air over liquid nitrogen will become more compelling.

 

From the discussion presented in this chapter we conclude:

• There is a sporadic history of failed attempts to exploit liquid air as an energy vector, but technological breakthroughs and market evolution since the turn of the century make it worth investigating once again.

• Liquid air is not currently produced commercially but easily could be. There is a large surplus of liquid nitrogen gas available for liquefaction, and this would offer similar thermo-physical properties to liquid air.

• Liquid air and/or nitrogen offer a means to exploit myriad sources of waste heat.

• A number of promising technologies to exploit liquid air have either been demonstrated already or are in development.

 

Endnotes

¹
The World, New York, June 24th 1900

²
Cryogenic engine system and method. E.H. Schwartzman. Patent number US3451342, 1969.

³
Non-pollution motors including, cryogenic fluid as the motive means, H.L. Boese and T.R. Hencey, Patent number US3681609, 1972.

⁴
Storage of Electrical Energy Using Supercritical Liquid Air, E.M. Smith, Proc. Inst. Mech. Eng., pp289-298, 1977.

⁵
Engine systems using liquid air and combustable fuel, A.L. Latter et al., Patent number US4359118, 1982.

⁶
The cryogenic nitrogen automotive engine, J.L. Dooley and R.P. Hammond, Mechanical Engineering, pp66–73, October 1984.

⁷
Cryogenic heat engines for powering zero emission vehicles, C.A. Ordonez et al., ASME IMEC, PID-25620, 2001.

⁸
Development of Generator of Liquid Air Storage Energy System, Kenji Kishimoto et al., Mitsubishi Heavy Industries Technical Review, October 1998.

⁹
Inventor’s creation not just hot air, BBC News, 2 October 2012, http://www.bbc.co.uk/news/technology-19802190.

¹⁰
Development first in the ukraine demonstrational model of non-polluting automobile with cryogenic powerplant, A.N. Turenko et al., ISJAEE, 4 (24), 2005.

¹¹

Indirect CO2 emissions compensation: Benchmark proposal for Air Separation Plants, European Industrial Gases Association (EIGA), position paper #33, December 2010, http://eiga.org/fileadmin/docs_pubs/PP-33-Indirect_CO2_emissions_compensation_Benchmark_proposal_for_Air_Separation_Plants.pdf

¹²
Ibid.

¹³
Results from performance tests carried out by Highview at the Slough site, personal communication, February 2013. 

¹⁴
Because of its small scale the pilot plant operates at a subcritical pressure (peak process pressure 13bar), whereas at commercial scale the plant would operate at a supercritical pressure (>38bar). This means that in the pilot plant the majority of the air is reduced to liquid by means of cooling to the saturation point, giving a low efficiency of 7-12%. In the commercial plant the air is cooled to a level above the saturation temperature and then expanded through a Joule-Thomson valve to reduce to liquid. This is a significant factor in the higher efficiency of a commercial scale plant, calculated to be 60%. Highview Power Storage, personal communication February 2013. For more detail see Appendix 1.

¹⁵
National Grid, personal communication.

¹⁶
Nitrogen liquefaction requires 549kWh/tonne (European Industrial Gases Association (EIGA), December 2010). 8,500 tonnes x 0.55MWh = 4,675MWh.

¹⁷
2.8GWh x 365 = 1,022GWh per year, or 1,022,000,000kWh. Average annual household electricity consumption is 3,300kWh. (http://www.ofgem.gov.uk/Media/FactSheets/Documents1/domestic%20energy%20consump%20
fig%20FS.pdf). 1,022,000,000 / 3,300 = 309,696.

¹⁸
We assume a small car has an energy requirement of 0.13kWh/km, on the basis that the Nissan Leaf has a 24kWh battery and range of 175km (24/175 = 0.13). At a practical energy density of 0.1kWh/kg this translates to a requirement of 1.3kg of liquid air per km for a liquid air prime mover, and 1.04kg/km for one operating with the benefit of waste heat from an ICE engine. The UK could produce 8,500T (8.5 million kg) per day of additional liquid nitrogen. At 1.3kg/km this would equate to 6.5m vehicle miles, increasing to more than 8m vehicle miles with waste heat. Cf http://www.nissan.co.uk/?cid=ps-63_296991&gclid=CIX476ulyrUCFcbKtAodfw0AbA#vehicles/electric-vehicles/electric-leaf/leaf/pricing-and-specifications/brochure.

¹⁹
http://www.stirlingcryogenics.com/stirling-cryogenics-contact/

²⁰
For example, a tank containing 60 tonnes of liquid air based with 0.5% nitrogen boil-off per day would see oxygen concentration rise by 0.1% per day. Liquid air is typically considered to be enriched at 23% oxygen. At this rate it would take about 17days to reach this level.

برچسب‌ها: liquid air

برچسب‌ها: معرفی انواع روش های تولید گاز نیتروژن

جدا سازی هوا (Air separation unit) به فرایند جداسازی هوای اتمسفر به اجزای اصلی تشکیل دهنده اش مانند اکسیژن، نیتروژن، آرگون و سایر گازهای نجیب گفته می شود.

اکسیژن به جهت کاربرد وسیع آن از لحاظ میزان تولید رتبه سوم را در میان مواد شیمیایی به خود اختصاص داده است و در بسیاری از واحدهای صنعتی به عنوان یکی از عناصر مورد نیاز حضور دارد، در از کاربردهای آن می توان به صنایعی نظیر فولاد، متالورژی، تولید فلزات غیر آهنی،جوشکاری ، برش فلزات، سیمان، سرامیک، پالایش نفت و کاغذ سازی و... اشاره کرد.

رایج ترین شیوه جداسازی هوا (ASU)، تقطیر (تبریدی) کرایوژنیک است. روش های غیر تبرید دیگری مانند جذب سطحی، فرایند شیمیایی، جداسازی غشایی، نیز در واحدهای تجاری برای جدا سازی یک جز از هوای معمولی استفاده می شود. اکسیژن با خلوص بالا، نیتروژن و آرگون که در ساخت دستگاه های نیمه هادی مورد استفاده قرار می گیرند می تواند از روش کرایوژنیک تولید شود. 

فرایند کرایوژنیک مایعات

در این فرایند هوا را تا مایع شدن سرد می کنند، سپس این مایعات با دمای جوش متفاوت وارد ستون تقطیر می شود. این فرایند می تواند گاز با خلوص بالا تولید کند اما پروسه ای انرژی بر است. این روش توسط دکتر کارل فوند لیند ابداع شد و امروزه در جاهایی که نیاز به تولید گازهای با خلوص بالاست کاربرد دارد. فرایند جداساز برودتی نیاز به مبدل های حرارتی خاص و ستون های جداساز با راندمان بالا دارند. تمام انرژی مورد نیاز تبرید از طریق کمپرسورهای هوا در ورودی تامین می شود.

فرایند کرایوژنیک صنعتی

  این روش جداسازی در حال حاضر یکی از پرهزینه ترین و  کارامد ترین روش های تولید بالای اکسیژن، نیتروژن و گاز نجیب مایع در صنعت می باشد. واحد های جداساز با استفاده از چند ستون تقطیر فرایند تولید گازهای مایع با خلوص بالا از هوای فشرده را انجام می دهند. در این فن آوری نیتروژن خالص به عنوان یک محصول فرعی تولید می شود. تحقیقات نشان می دهد تولید اکسیژن با شیوه کرایوژنیک در سال های اخیر افزایش یافته است. با توجه به نیاز بازار پیش بینی شده در آینده ای نزدیک توانایی تولید به 5000 تن در روز خواهد رسید. شکل زیر 5 واحد عملیات اصلی مورد نیاز جداسازی هوا و تولید محصولات مفید را نشان می دهد. هوا از ابتدا برای حذف آلاینده ها تصفیه شده و وارد کمپرسور می شود. سپس تا دمای بسیار پایین سرد می شود تا اکسیژن ،نیتروژن و آرگون به فرم مقطر در آیند. تنظیمات متعددی از مبدل حرارتی می تواند هوا را به محصولات مورد نیاز مجزا سازد. نوع فرایند بر اساس مقدار خلوص و جریان محصول می تواند متفاوت باشد. خواص انواع فرایندهای برودتی برای جداسازی هوا می تواند بستگی مستقیم به میزان فشار در ورودی یا خروجی محصولات داشته باشد.

برای رسیدن به دمای پایین در تقطیر نیاز به تجهیزات سرد کننده، محفظه عایق و یک چرخه تبرید است که با استفاده از روش ژول_تامسون، عمل می کند. فرایند تقطیر شامل مراحل زیر است:

1. هوا با این مشخصات وارد سیستم می شود. 99% حجم آن را گازهای اکسیژن و نیتروژن تشکیل می دهند و باقی گازها شامل آرگون، کربن دی اکسید، زنون و سایر گازهای نجیب می باشد.
2. برای از بین برن ناخالصی ها تصفیه مقدماتی هوا پیش از تجزیه به اجزای سازنده اش صورت می گیرد.
3. هوا در فشاری حدود 5 تا 10  bar مکش می شود. فشار های مختلف برای راندمان های متفاوت می باشد.
4. در این بخش خنک کاری ابتدایی هوا تا -180 ºC صورت می گیرد. هوا همانطور که در ستون مایع بالا می رود سردتر شده تا جایی که تبدیل به مایع شود.
5. در ستون تقطیر، هوا در یک فرایند کاملا فیزیکی به اجزای سازنده اش تبدیل می شود. مایع روی ستون سینی جمع می گرد. ابتدا اکسیژن با دمای جوش بالاتر (-183 ºC ) متراکم می شود، پس از آن نیتروژن با دمای جوش پایین تر ( -196 ºC ) میل به کندانس دارد. گازهای نیتروژن در بالای ستون جمع شده و اکسیژن مایع در پایین ستون. اکسیژن در پایین تبخیر می شود در حالیکه در بالا نیتروژن در حال کندانس است این فرایند تا جایی ادامه پیدا می کند که به سطح خلوص مورد نظر برسیم.
6. همان طور که در شکل نشان داده شده یک ستون مجزا نیز برای جمع آوری گازهای نجیب وجود دارد. ترکیبات باید بیشتر خالص شوند. در دستگاه های پیشرفته تر ظرفیت تولید 45000 m³ اکسیژن ، 1700 m³ گاز آرگون و 91 m³ گازهای نجیب در ساعت وجود دارد که 60 تا 85% خالص است.
7. اکسیژن و نیتروژن تولید شده با فشار 40barr وارد خطوط شبکه می شوند.
8. اکسیژن مایع، نیتروژن و آرگون در داخل مخازن پر می شوند.
9. بخشی به تانکرهای جاده ای منتقل شده
10. بخشی هم با فشار 300bar وارد مخازن فولادی می  گردد.

منابع و پیوندها

گرد آوری شده توسط دپارتمان پژوهشی شرکت پاکمن

www.uigi.com/compair.html

http://www.airproducts.com

 

برچسب‌ها: جداسازهای هوا_ روش کرایوژنیک

برچسب‌ها: مولدهای اکسیژن و نیتروژن به روش کرایوژنیک, Cryogenic

 

فیوزینگ شیشه از ابتدا با ویدیو

http://www.bullseyeglass.com/methods-ideas/technotes-4-heat-a-glass.html

 

Mosaic glass(embroidered glass)is structured by pressing three layer-tempered glass together with various designs that is assembled with a frame of copper-strips. It owns a lot of characteristics such as luxury, beautiful, warm-keeping, heatproof, anti-impacting, theft proof and free condensation, etc. With a good appearance of smooth arts line, beautiful color with a unique design, the glass is especially suitable for being used in bedroom, bath/shower room, balcony and hall/lobby, etc.

Applications of mosaic glass:

Doors and windows are the soul of building just like the eyes are the windows of the mind. A beautiful and picturesque door or window would ease your life pleasantly, creating a comfortable enjoyment for you.

 

 

برچسب‌ها: شیشه موزاییک طرح های زیبا

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