| Introduction:
Heat pipe is a kind of new heat transfer element with ultra-high thermal conductivity.Heat pipe originated in the 1960s in the United States.A stainless steel- hot water pipe was first placed in earth orbit satellites and ran successfully in 1967. Heat pipe theory had been paid a high degree of attention from the beginning when it was brought forward by scientists from different countries ,and a lot of research work has been launched, which promoted the quick development of heat pipe technology.Heat pipe technology was mainly used in aerospace field at the beginning. Heat pipe has been studied in China since the 1970s.Products like heat pipe gas - gas heat exchanger,heat pipe gas - water heat exchangers,heat pipe waste heat boiler,heat pipe steam generator and heat pipe hot air stove,etc have been developed since the 1980s, which are widely used in the range of the building materials industry, metallurgical industry, chemicals and petrochemicals, power engineering, textile industry, glass industry, electrical and electronic engineering and other fields.
Working principle:
Heat pipe is made of steel,copper,aluminum tubes,filled with heat conduction materials,and is pumped into vacuum and sealed.Materials in the pipe are of a variety of mixture of inorganic active metal and its compounds,with an unusual heat activity and heat sensitivity.Heat pipe absorbs heat in heat condition and discharges heat in cold condition.This kind of heat superconduct is activated under certain temperature,and transfers in the form of molecule shake and changes,whose super thermal conductivity is generally around 10,000 times of normal metals.The transmission temperature does not decay and is able to transfer in fast speed (the speed of sound).
Heat pipe is the heat transfer components that transfers heat relying on its internal liquid phase changes,with an unusual hot activity and heat sensitivity.Heat pipe absorbs heat in heat condition and discharges heat in cold condition.
Basic characteristics:
 Super thermal conductivity: fast thermal conductivity speed,strong intensity,high efficiency,thermal conductivity speed can be up to the speed of sound. Good isothermal characteristics: good isothermal characteristics makes the heat pipe transfer great heat in a very small temperature difference and in small heat resistance. Heat flow density variability: heat pipe can change the area of evaporation part or cooling part independly,that is,input heat in small area,and output heat in great cooling area or input heat in big area,and output heat in small cooling area. Safety and reliability: without overpressure in pipe,with dry hot enduration.Internal pressure of the the heat pipe does not change with temperature changes in the vaporization of the liquid. Environmental adaptation: without environmental constraints,the pipe can be designed individually according to the environmental needs. Wide application:superconducting heat pipe has great shape flexibility, wide range of applications and is adapt to all kinds of poor working conditions.
Working principle of heat pipe waste heat recovery device:
Heat pipe is the main heat transfer components of waste heat recovery device,which is essentially different with ordinary heat exchangers. Transfer efficiency can be up to 98 percent in heat pipe waste heat recovery device,of which ordinary heat exchanger is unable to reach.  Heat pipe waste heat recovery device is small in size,only 1/3 of ordinary heat exchangers.Its working principle is as shown below: Gas flue is in the left channel,clean air (water or other media)is in the right channel, a clapboard separates in the middle preventing interference. High-temperature gas flows from the left channel and washes down the heat pipe,with the flue gas temperature> 30 ¡æ,The heat pipe will be activated and automatically conduct heat to the right,then the left of heat pipe absorbs heat,high temperature gas flows through the heat pipe and the temperature decreases.Heat pipe abosorbs the heat and transfers it to the right.Clean air at room temperature(water or other medium) washes dowm heat pipe opposite along the right of the access in the promotion of blower.Then the right side discharges heat,heating clean air (water or other medium),the air flows through the heat pipe and the temperature rises.
Characteristic of heat pipe waste heat recovery device£º
High reliability and safety:
Conventional heat transfer equipment generally is septate heat transfer.Hot and cold fluid flows separately in the wall on both sides,if the wall leaks,it will cause losses of production stop.While heat pipe waste heat recovery device is the twice septate heat transfer,in which heat flows through the wall of evaporation part and condensation part and then reaches the fluid.
Heat pipe waste heat recovery device is of high transfer efficiency and significant energy saving efficiency.
Good anti-corrosion ability of heat pipe waste heat recovery device
Heat pipe wall temperature can be adjusted,and it can be adjusted above the low-temperature fluid dew point through the appropriate heat flow transformation,preventing dew point corrosion and ensuring long-term operation of equipments.Avoid smoke dew point,so that dust is difficult to bond on the fin and the pipe wall.At the same time,heat pipe vibrates in the heat conduction process,so that the ash is difficult to adhere to the wall and fins,which will not be blocked by ash.
Installation and structure layout flexibility:
Without changing the original system in the installation process for pipe waste heat recovery device,structural design and location layout is very flexible and can adapt to all kinds of complicated occasions.
Long life: Life for more than 10 years,single heat pipe is removable and replaceable,simple maintenance and low cost.
Short payback period: Usually all the investment can be obtained in six months to one year.
Application of heat pipe waste heat recovery device in industrial waste heat recycle:
Waste heat is the energy not be used in equipment in certain economic and technological conditions,which is redundant and obsolete energy. It includes high-temperature waste heat emissions,waste heat of cooling medium,waste heat of waste steam and wastewater, high-temperature waste heat products and slag, waste heat of chemical reaction, flammable liquid waste, waste heat of waste material and waste pressure of high-pressure fluid,etc, more than seven categories. According to the survey, the waste heat in all sectors is about 17% -60% of its total resources consumption,of which 60 percent of the waste heat is recyclable.
Waste heat recovery and waste heat generator applications
Application in the chemical and petrochemical industry:
Waste heat recovery of uplink and downlink coal gas in small ammonia plant, waste heat recovery of uplink and downlink coal gas in medium ammonia plant , waste heat recovery of compound ammonia blown gas combustion , waste heat recovery of compound ammonia transformation furnace Sec1, waste heat recovery of 300,000 tons / year compound ammonia transformation furnace Sec2.
Application in sulphuric acid industry:
Waste heat recovery in fluidized layer of fluidized bed roaster in sulfuric acid production; 55,000 tons of steam can be recycled in an sulphuric acid plant with annual producing capacity of 100,000 tons; Waste heat recovery of SO2 gas from the high-temperature gas furnace;105,000 tons of steam can be recycled in an ulphuric acid factory with an annual output of 100,000 tons,which worths about 6 million yuan if transferred into electricity;
Application in hydrochloric acid, nitric acid furnace: Ibid.
Application in petrochemical industry :
Waste heat recovery of hydrocarbons in the furnace (working temperature is about 750-900 ¡æ) waste heat recovery of ethylbenzene in dehydrogenation reactor; waste heat recovery of cyclohexanol dehydrogenation reactor; waste heat recovery in catalysis, cracking and renewable device.; waste heat recovery of other furnaces;
Application in building materials industry:
Waste heat recovery in the hot wind stove of kaolin spray drying; Waste heat recovery of glass furnace; Waste heat recovery of cement kilns;Waste heat recovery of various of ceramic inverted kilns and tunnel burning stoves.
Application in the metallurgical industry:
Waste heat recovery of continuous steel heating furnace and steel soaking pit; Waste heat recovery of blank pieces in the furnace;Waste heat recovery of wire annealing furnace;Waste heat recycle of sintering machine,with a 180 M2 of sintering machine as an example,the recoverable steam can be amounted to 10-22 tons / per hour;
There are many ways of waste heat recovery and utilizations:
Generally speaking,comprehensive utilization of waste heat is the best£» followed by is the direct utilization£»the third is the indirect utilization(used to generate steam for power generation). The rational use sequence of waste heat steam is:the joint use of driving power;joint use of power generation£»use of production technology; use of life need;condensing use for power generation. The rational use sequence of waste heat water is: for the perennial use of production technology;return to boilers and power generation use;use of life need. The rational use sequence of waste heat air is:production use;HVAC use; power use;power generation use.
Waste heat recovery technology and method:
Separate heat pipe waste heat recovery technologies;overall heat pipe waste heat recover technologies; waste heat recover method: different ways of design and method of waste heat recovery can bring different results, that is,the waste heat or the steam recycled is completely different.
The picture above is the use of heat pipe in solving the problem of frozen soil of Qinghai-Tibet Railway.This kind of heat pipe is seven meters long, and is carbon seamless steel pipe.It is buried five meters underground and two meters out of the ground.It is filled with liquid ammonia inside, which brings ¡°cold air¡± of the frozen soil layer to the soil surface,and keep the surface freezing and hard and brings heat of soil surface to the air through the "fin" on the surface.Long pipes,like automatic hot and cold transmission "air conditioners",will maintain the frozen state of roadbed for ever.
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