From PESWiki

Down-Draft Energy Towers, proposed by Robert J. Rohatensky, are like a funnel, with a method to remove heat at the top of the tower causing the cold heavy air to fall down the tower and drive electrical generation turbines.

This initial design has a fundamental flaw and was upgraded to a new design at: Directory:Bi-Directional Energy Tower

-- Author, Rohar1 13:24, 1 Sep 2006 (EDT)

The following page, which pointed out the flaw and led to the upgrade, is kept here for historic archive purposes.

Assessment 

New Energy Congress member and PES Network R&D Director, Ken Rauen, does not think this design will serve as an energy generation method. He says that at best, it is an energy-requiring dehumidifier.

Proponent Websites

• http://www.energytower.org - Published in Aug. 2006
  • Self Powered Heat Pump (http://www.energytower.org/self_powered_heat_pump.html)
  • Steam Powered Water Pump (http://www.energytower.org/steam_water_pump.html)

How it Works

A down draft chimney utilizes a heat pump at the top of the tower to extract energy and cool air. The cold heavy air falls and creates a downward pressure to drive electrical generation turbines. This is opposite the idea of a solar tower and uses the ground as a solar collector which greatly reduces costs and land requirements.

Contributed Improvements to Displayed Design

2006-08-26 (Robert J. Rohatensky) - A rotating air intake at the top controlled to face into prevailing winds would increase performance and provide radiant heat insulation over the cooling coils. It should also improve system startup.

Benefits

Quoting from http://www.energytower.org

• The design does not require a water source and the construction may be placed anywhere there is daytime heating of air
• The more heat (energy) captured at the top of the tower by the cooling system, the larger the force of the air down the tower and through the turbine. This should provide a highly efficient system where an increase of heat capture at the top provides an increase of the power output the lower turbine.
• The condensation on the cooling coils at the top may be used to provide a clean domestic water source at distilled water quality as a by-product.
• If I understand Professor Zaslavsky's design, his intent is to use the weight of moist, evaporatively cooled air. I propose that cooling the air with refrigerant coils sufficiently will cause air with 100% relative humidity if it contains any humidity at all prior to cooling. Cooling the air with a water mist will only cool until the air is 100% relative humidity and then any additional water added to the system is innefficient, only cooling the air by the temperature difference of the source water. Any energy captured from the falling water is lower than the energy required to pump it to the top.
• A refrigerative system will work in all relative humidity situations, producing more water by-product in high humidity situations. The total energy output should be based on the temperature difference generated at the inside of the top of the tower and the external air at the bottom. This allows this system to be placed in extreme hot arid locations with no available water source and it will produce water if there is any moisture in the air.
• The energy required to pump water to the top of the tower is eliminated and replaced with a heat pump system that should have a positive energy gain (4-10 times the input energy for existing heat pump systems).
• The system should operate in a wide range of climates with the limitation that there is sufficient heat at ground level to allow for a large air temperature difference to be created by the cooling coils.

No Patents / Open Source

Rohatensky has published his concept openly on the Internet, rather than pursuing a patent. He supplies the following reasoning.

"[I would like to] comment on ... the explanation of why I posted the idea on the Internet rather than to try and secure a patent. It's a difficult concept to explain in a capitalistic society and not have people assume that the idea has no value because I am not hording it trying to get rich from it."

"My reasoning follows the Linus Torvalds approach with Linux and why Linux has done so well against established commercial Unix and Microsoft when other commercial competition with Microsoft was crushed. Even in the case of a large company like IBM trying to compete with Windows (OS/2), it was a failure. I think that companies trying to compete with the estabished fossil fuel industry will have even more difficulty than competing with MicroSoft. The example from Linux and other open source projects shows that it is possible to compete with large corporations when you aren't trying to make money.

1. "I want to see the commoditization of the system as soon as possible
2. "I believe that any idea that will cause the fossil fuel industry to lose profit will be seized by the industry for profit (the companies have an obligation to their shareholders)
3. "I thought that if I am willing to waive making a profit from the idea, it would entice others that hopefully know more than me to help with the project (this is what made Linux a success)
4. "I have a wife, 3 kids, a great dog, a pretty good career and I am reasonably happy. I am believe that if I made a significant contribution to making the world a better place, I would be happier than if I was rich."

He also says:

"I hope that resources with the technical and financial ability to move this idea through the detail design, prototype, performance improvement and full scale implementation stages will see the merit and assist in this project."

Original Design (Water Spray Cooling Method)

• "Solar Energy Without a Collector" (http://www.consortia.org.il/ConSolar/Sabin/Zas/ZasTOC.html) - Dan Zaslavlsky, Technion - Israel Institute of Technology - The central idea is to cool the hot and dry air of the desert by a fine spray of water (evaporative cooling). The cooled air contracts and obtains a higher density thereby falling and creating a downdraft. The hot air is supplied day and night. Thus, an Energy Tower will produce electricity day and night.
• www.energytower.net - The “Energy Towersâ€? is a world changing clean energy technology developed by Professor Dan Zaslavsky at the Technion, Israel. The Energy Tower has the ability to produce enormous amounts of electricity from two inexhaustible sources, hot dry air and sea water while producing no greenhouse gases.
• Energy Towers (http://physicaplus.org.il/zope/home/en/1124811264/1137833043_en) - The cost of electricity from the Energy Towers is even lower than the lower limit of costs from coal and gas at 5% interest rate. North Africa has the potential to provide the whole of Europe with clean renewable electricity. Furthermore, it is estimated that seawater desalination could be obtained with some 45% cost reduction. The overall volume of desalinated water could reach 10-20 times the Nile River. Thus, north Africa could become the food and energy store for Europe.
• Sharav Sluices Ltd. (http://www.technion.ac.il/technion/dimotech/sharav.html) recently received seed money to begin designing a scaled up prototype of its unique technology to produce electricity from dry desert air and brackish or sea water. Israel’s Ministry of Energy is endorsing the project which will produce power at a cost of 2.5 to 3.5 cents per kwh. A by-product of the technology will be desalinated water at a cost of approximately half of today’s cost per cubic meter. See also Professor Zaslavsky's Sharav Sluices (http://techunix.technion.ac.il/~cerekek/sluice.htm).
• Energy Towers: Pros and Cons of the Arubot Sharav Alternative Energy Proposal (http://www.macdialup.com/zwilliams/arubot.htm)
• Interim Report June 2005 (http://www.ecmwf.int/about/special_projects/czisch_enrgy-towers-global-potential/report_2005_extended.pdf) (pdf file) - Evaluation of the potential of electricity and desalinated water supply by using technology of "Energy Towers" for Australia and America

In the News

• Energy Towers Touted as Future Source of Electricity (http://www.jewishmonmouth.org/content_display.html?ArticleID=94865) - The idea is the brain-child of Professor Dan Zaslavsky and makes use of the convection of air through a hollow tower. Cold water droplets sprayed into the top of tower evaporate, cooling the air which then sinks to the bottom of the tower and turns the turbines. Although the total area required for such a plant would be twice that of a conventional power plant, only a tenth of the area is required to generate the same electricity from solar panels. (Jewish Federation of Greater Monmouth County; September 14, 2003)
• French backer close to investing in sharav energy tower project (http://www.haaretz.com/hasen/pages/ShArt.jhtml?itemNo=384803&contrassID=2&subContrassID=1&sbSubContrassID=0&listSrc=Y) - The giant French industrial conglomerate Alstom is in advanced negotiations to invest in the establishment of an "Energy Tower". Plans call for the construction of a 1,000-meter-high cylindrical tower with a 400-meter diameter. Such a tower has yet to be built anywhere in the world. One Energy Tower could produce around 800 megawatts a year of power at a cost of about 4.5 cents per kilowatt-hour. (Haaretz)

Comments

De-humidifier, yes; Energy tower, no

On Aug. 31, 2006, New Energy Congress member and PES Network R&D Director, Ken Rauen, wrote:

Classical perpetual motion that is truly laughable.

It should NOT be called an energy tower. Call it a water tower, instead. This is the same concept as a dehumidifier (water is collected from the air), except its efficiency is enhanced.

As shown, the "energy tower" will not generate any net electricity. To the contrary, it will take some electricity input to operate. That small input could be a solar panel.

The opening drawing and description is a perpetual motion machine that won't work! Using a heat pump to cool air and cause a downdraft in a chimney and then spin a turbine with a generator to get back the input energy of the heat pump is a washout at best.

http://www.consortia.org.il/ConSolar/Sabin/Zas/Zas3.html [is worth mention, and] cites a different mechanism. This one sprays cool water into hot, dry air. The water cools the air and then evaporates, providing the energy to run this heat engine that does not have a heat pump associated with it! This one CONSUMES water, whereas the prior one in question produces water.

--Rohar1 20:06, 31 Aug 2006 (EDT) wrote:

This was not intended as perpetual motion, it was intended as a method of collecting solar energy. I have learned some things since my original posting and now I understand that without a low temperature heat sink it is breaking the Second Law of Thermodynamics to expect to be able to pull energy from the ambient air with the heat pump portion. I think it can transfer heat very efficiently because it doesn't have to move the input and output media, but unless someone can come up with something colder than the ambient air I was mistaken in being able to get anything positive from the Heat Pump. I am still not convinced that the tower as a whole cannot be made energy positive using a cooling method that will allow it to work in sub-zero temperatures.

Updraft Tower Preferable

On Aug. 28, 2006, New Energy Congress Member, Tai Robinson said:

I think an updraft tower would be much simpler and not require coolant energy. A greenhouse garden full of lush foods at the bottom heating air that escapes out the top of a tower with wind generators inside of it. Make food and energy.

Rohar1 21:14, 29 Aug 2006 (EDT) replied:

This is a good comment and demonstrates a lot of the general misunderstanding of the Conservation of Energy (http://en.wikipedia.org/wiki/Conservation_of_energy). "Cooling" is transferring energy (heat) out of something to something else. In the case of the Energy Tower, it's converting heat energy into electricity. I think that the misconception that "cooling" somehow requires energy (it really is the opposite) probably comes from the modern day experience with refrigerators and air conditioners. The refrigeration principle is based on the transferring heat from one space to another expending energy with compressors and fans, which is an extremely inefficient way to solve the problem of cooling a given space. The constant exposure to air conditioners and refrigerators in modern life has given people a misunderstanding of what "cooling" actually is.

Once you understand the Conservation of Energy, a lot of the modern day problems are easy to solve. For example, if you use the steam engine principle of converting heat into mechanical energy, but use something with a very low boiling point (i.e. refrigerants or liquid nitrogen) you can cool a given space and use that energy to do work. The air conditioner and refrigerator were a very inefficient method of cooling spaces that flourished because energy was cheap. It would make much more sense to cool our food and buildings by converting that heat energy into something useful like electricity. It would also mean that on a hot summer day, buildings would be producing more energy, not browning out the grid pumping heat out into an already hot space.

How about "Heatsink" instead of a heatpump?

On Aug. 29, 2006, User:Dewbacca wrote:

How about using a "Heatsink" instead of a heatpump? More specificly use an anhydrous ammonia heat absorber at the top of the tower. At the bottom will be a seperate device to use the heat taken from the top (passively).

--Rohar1 08:54, 31 Aug 2006 (EDT) wrote: This would work, but dissipating the heat would be "wasting" the energy. The amount of energy that would be output by dissipating the heat at the lower portion of the tower is trivial to the amount of heat the sun is adding to the ground If you are trying to extract energy ("cool"), it might as well be used for something useful.

Second Law of Thermodynamics Qualms

On Aug. 30, 2006, User:Jameson wrote:

Mr. Rohatensky, I believe you need to brush up on your thermodynamics. The Second Law of Thermodynamics essentially says that heat cannot pass from a colder to a warmer body. This is exactly why modern systems require energy input for refrigeration, energy needs to be expended to pump heat from a lower temperature reservoir to a higher temperature reservoir. Your proposed energy tower would actually require more energy to run than it would output.

To use your example of using liquid nitrogen as a refrigerant: You can use the liquid nitrogen to cool off the space, then use the boiled off nitrogen to run a turbine and produce electricity. The problem lies in re-liquefying that nitrogen for another pass, you need a lower temperature reservoir to accomplish this. Using steam at high temperatures in a turbine is fine because ambient temperature air or water can be used to re-condense the steam.

Rohar1 21:02, 30 Aug 2006 (EDT) replies:

No, if what you were saying were true the common heat pump used in home and pool heating would be less efficient than direct heating, and there are many production examples that achieve 4:1 output including driving the transfer systems of the input and output media.

A heat pump transfers more energy than it uses because of the "bump" in the amount of energy matter requires to cause a Phase Change or State Change (boiling or freezing), and that changing the pressure of the matter changes the temperature the state change occurs (i.e. water boils at a higher temperature when it is under pressure). It's a proven fact that the amount of energy required to change the pressure is substantially less than the amount of energy that can be transferred.

Professor Zaslavsky (http://www.consortia.org.il/ConSolar/Sabin/Zas/ZasTOC.html) has done the calculations for the Water Spray Cooling Tower (http://www.energytower.net) which uses the state change of evaporation to cool the air and this shows that even if you expend the energy to pump water up the tower to cool the air, the state change that occurs when the water evaporates creates a very positive output energy of the tower (including the energy expended to pump the water).

The negative part of using an "open" water system is that it requires a water source, depends on the relative humidity of the air and won't work at all in sub-zero climates.

My improvement to this design works on the same state change principle and I am only trying to achieve enough efficiency in the top cooling system to lower the air temperature and drive the lower turbines. Using a closed system has less efficiency than spraying water into the air because of the heat transfer through the heat exchangers, but it doesn't require pumping the water. If the heat pump only "breaks even", the lower turbines driven by the force of the cooled air are what produce the major portion of the electrical output. I believe that if some thought is put into the cooling section and the same state change principles are leveraged as the water spray method, the tower can be even more efficient (and not turn into a huge ice sculpture in Canada).

Jameson 07:28, 31 Aug 2006 (EDT) replies:

I agree that spraying water at the top of the tower will work and it does have the downsides you mentioned. I also agree that a heat pump will transfer more energy in the form of heat than is input in the form of electricity. This breaks no laws because no heat is being created, it is just being moved. In my first comment I was mainly trying to disprove your idea that the refrigeration loop could actually make electricity. Now it seems you agree that it will take electricity, but you believe it will still be efficient enough for the whole system to be energy positive.

Heat pumps and refrigerators usually have a Coefficient of Performance of 3 or 4, meaning they will transfer 3 or 4 times more energy than was input. Lets say your heat pump does have a COP of 4 and you are getting 100 MW of cooling for 25 MW of input electricity. The intake temperature at the top of the tower would be around 70 degrees Fahrenheit and after the refrigeration step the temperature goes down 55 degrees F, a typical temperature drop for refrigeration systems. The cold air will cause a downdraft and spin the turbines at the bottom of the tower. Using Professor Zaslavsky's (http://www.iset.uni-kassel.de/abt/w3-w/projekte/new_et-brochure_zaslavsky.pdf) own numbers, this downdraft mechanism has a maximum efficiency of 2.8%. This means your cooling effect of 100 MW will output 2.8 MW by the turbines at the bottom of the tower. For the original Energy Tower design using sprayed water at the top of the tower, 2.8% is not bad because the seawater is free and the whole system will be energy positive. In the proposed Energy Tower using a refrigeration system, the system would not be energy positive because 25 MW has gone in, with 2.8 MW coming out.

This 2.8% is also the thermal efficiency of a Carnot cycle operating on a 15 degree F temperature differential. A Carnot cycle is the most efficient cycle that can operate between two constant-temperature reservoirs. No actual machine can match this efficiency, it represents the absolute maximum. The maximum Carnot COP of a heat pump operating at this temperature would be 35, the inverse of the heat engine efficiency (1/0.028). Using an ideal Carnot cycle the best you could do is break even, but in real life the efficiencies will be much lower, leading to an energy negative system.

I suggest you pick up a Thermodynamics text and read up on this subject.

--Rohar1 09:11, 31 Aug 2006 (EDT) wrote:

Thanks for the input and you are totally correct if you are talking about using a heat pump in the classic sense and dissipating the output heat rather than using it. Your explanation answers the above question regarding using a "Heat Sink" and transferring the heat to the lower portion of the tower much better than I was able to. What I am talking about is not wasting the output heat but using it to do work, which you are totally missing in your input/output calculation.

Using sea water in the Water Spray Energy Tower is not "free", you have to pump it to the top of the tower. The change of state of evaporating the water takes much more energy out of the air (lowering temperature, increasing the airs density) than the pump energy and the system is energy positive even though only 2.8% of the the energy is captured. My design is using the same change of state, but in a closed system with lower boiling point fluids.

You also have the Carnot COP backwards. In the ideal Carnot cycle I would only be able to see a 2.8% efficient energy net gain converting the heat in the air into mechanical energy. The input media is warm air and there is an unlimited supply. The down draft effect of putting this "low temperature steam engine" at the top of a tower means that it doesn't have to expend energy transferring huge amounts of warm air through the heat exchanger to capture 2.8% of the energy.

Jameson 17:45, 31 Aug 2006 (EDT) replies:

First I will respond to the first paragraph of your latest reply, including an additional heat engine (like a steam turbine) to capture the waste heat from the heat pump.

Using the waste heat from the condenser of the heat pump will not make the system energy positive, even using a Carnot cycle (remember that anything constructed in real life will always have an efficiency lower than a Carnot cycle). I did make one over-simplification in my last comment, the heat pump would actually operate on a temperature differential of 35 degrees F. This is because the condenser would need to be around 90 degrees F to actually transfer heat into the room temperature air. This would lower the possible COP to 15, but the efficiency of the turbines at the bottom of the tower would remain at 2.8%. The additional heat engine you propose would operate on a temperature differential of 20 degrees F (90 degrees at the condenser, 70 degree ambient air). This would give the second heat engine an efficiency of 3.6%. If we put 1 MW of electricity into this ideal heat pump with a COP of 15, 15 MW of cooling will be provided. The bottom heat engine will generate 0.42 MW from this cooling (2.8% efficiency) and the upper heat engine will generate 0.576 MW from the 16 MW of waste heat exiting the condenser (3.6% efficiency). This adds up .996 MW due to my rounded off numbers, but using exact numbers it would be 1 MW. Like I said before, the best that is possible would be breaking even.

Now to address the second paragraph: When I said the energy from water is free, I meant that no money is required to purchase the water.

Finally, addressing the third paragraph. No, I do not have the COP backwards, there is no way to generate electricity from ambient air without a lower temperature reservoir. I'm sourcing my information from Ch. 7 of Fundamentals of Thermodynamics, Sixth Edition by Richard E. Sonntag, Claus Borgnakke, and Gordon J. Van Wylen, the textbook I used in my Thermodynamics course. At the very least, you should look at the Wikipedia articles on the Carnot Cycle, Entropy and the Second Law of Thermodynamics for the reasoning. Here is one helpful quote from the Entropy article:

"An important law of physics, the second law of thermodynamics, states that the total entropy of any isolated thermodynamic system tends to increase over time, approaching a maximum value; and so, by implication, the entropy of the universe (i.e. the system and its surroundings), assumed as an isolated system, tends to increase. Two important consequences are that heat cannot of itself pass from a colder to a hotter body: i.e., it is impossible to transfer heat from a cold to a hot reservoir without at the same time converting a certain amount of work to heat. It is also impossible for any device that operates on a cycle to receive heat from a single reservoir and produce a net amount of work; it can only get useful work out of the heat if heat is at the same time transferred from a hot to a cold reservoir."

Unless you have access to a thermal reservoir at below room temperature, there is no way to generate electricity from room temperature air.

Rohar1 19:52, 31 Aug 2006 (EDT) replies:

1. You can convert heat energy into mechanical energy.

2. This isn't very efficient, so if you are trying to do this with a relatively small temperature change in air, you need a very large heat exchanger and you need to move a very large amount of air across it.

3. In the case of this down draft tower concept, no energy is being expended to move this large volume of air, once it is cooled it is heavier than the air on the outside of the tower and it falls on its own. The more air that moves, the more output of the lower turbines.

4. I have never claimed that any substatial amount of electricity can be generated by the top portion of the tower. My claim is that if what you are trying to do is cool air at an elevation and capture the energy with turbines at the bottom, you can do it efficiently enough with a closed system leveraging change of state, that the whole system has a very positive gain.

5. Look at the below patent.

Jameson 20:46, 31 Aug 2006 (EDT) replies:

1. Heat energy can be converted into mechanical energy; room temperature air is not considered a source of heat energy. An example: a nuclear reactor. The nuclear reactor fissions uranium atoms, this reaction releases energy in the form of heat, increasing the temperature of the fuel rods. Coolant in the form of water is passed over the fuel rods, since the water is at a lower temperature the heat will move from the fuel rods into the water. Let's say the fuel rods are at room temperature and the water is at room temperature. There is no temperature differential, therefore heat will not move from one to the other. This is why I say room temperature air will not generate electricity without a low temperature reservoir or a high temperature reservoir to provide the heat transfer. Heat has to be transferring from one entity to another to do work (in our case turn a turbine and generate electricity).

2. I'm not saying it is inefficient, I'm saying it will not even run without external electrical input.

3. To create this downdraft energy was expended to cool the air.

4. Both heat engines, the one at the top running on the waste heat from the heat pumps condenser and the downdraft mechanism acting as a secondary heat engine will never produce more energy than the input electricity for the heat pump.

5. The below patent is for thermal sources at above ambient temperature (i.e. solar panels and low quality geothermal sources). Since there is still a temperature variation, albeit smaller than a conventional power plant, it can viably produce electricity. It is a variation on the Rankine cycle where fluids with a low boiling point (ammonia, R-134a) are used instead of steam, similar to the Kalina Cycle.

I'm not trying to be annoying, I'm just trying to illustrate the laws of thermodynamics in use since the 1800's.

--Rohar1 00:17, 1 Sep 2006 (EDT) replies:

I don't think your annoying, your input is valuable. You have to remember that I'm not trying to make money off of this or scam investors. I am just going down a train of thought assuming that the water spray tower will work in arid climates, and trying to figure out a way to make it feasible in Canada where it's below zero 6 months of the year.

I read through what you have written several times and did as much reading as I could find on thermodynamics and I was mistaken in some of my understanding. I have presented this idea in what looks like a "Classic Perpetual Motion Machine of the Second Kind" and that was not my intent. I have to go back through all of this and revise my drawings and descriptions with what I have learned.

My thought goes like this as far as the water spray tower:

1. Fill a 5 gallon pail with water (~50 pounds)

2. Carry it up a 500' tower

Tired? :)

I seems like a lot of energy expended, but apparently the evaporation change of state will cause the air to cool enough to have a positive gain. I am taking this at face value, I am not a physics professor. I think that if bright people worldwide look at this (like yourself), there has to be a way to pull the energy out of the air in a cold climate in an efficient manner.

Jameson 20:46, 31 Aug 2006 (EDT) replies:

Thank you for your understanding. Thermodynamics is a tricky subject, it took me a 5 credit hour college course and two weeks working on refrigeration lab bench to understand most of it.

I'll admit that the water spraying Energy Tower does take quite a bit of energy to pump the water up to the top, but even modern coal plants need a lot of effort to make them run. Mine the coal from Wyoming, put it on a rail car and ship it to Michigan, offload the coal in a big pile, make dozers shift around the coal so it can be fed into a system of conveyer belts, pulverize the coal, feed the coal it into the boiler, force air into the boiler with multiple 4000 hp fans, then burn the mixture. This isn't counting the feedwater pump after the condenser, numerous other pumps around the plant and the multi-layered emissions control system.

My website (http://people.cedarville.edu/Student/jreichert/index2.html) details some other electricity generating concepts, some limited to geographical locations, but a few could work in a place like Canada. I created the website in my spare time, so it is not perfect, but like you I just wanted to get the word out on possible alternatives for electricity generation.

Related Patents

On August 15, 2006 the USPO granted patent 7,089,740 (http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=7,089,740.PN.&OS=PN/7,089,740&RS=PN/7,089,740) for a "Method of generating power from naturally occurring heat without fuels and motors using the same". This device basically is a Steam Engine using a different working fluid than water, but it demonstrates that transferring heat into mechanical energy can be done with a low temperature heat source.

Permissions

The quotations from Rohatensky's website (http://www.energytower.org) are with permission. Rohantensky first posted this page here, and has contributed to its development and dialogue.

Upgraded Version

The above initial design has a fundamental flaw and was upgraded to a new design at: Directory:Bi-Directional Energy Tower -- Author, Rohar1 13:24, 1 Sep 2006 (EDT)

See also

• Directory:Solar Tower
• Directory:Solar

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