A kind of efficient mechanical vapor recompression method for desalting seawater
Technical field
The present invention relates to a kind of method utilizing mechanical vapor recompression technology to carry out sea water desaltination.
Background technology
China is populous, and Freshwater resources are increasingly in short supply, and development desalination technology has great importance to the scarcity solving Freshwater resources.Desalination technology based on method of evaporating has the advantage such as product water water quality, cost that the method such as membrane sepn, ion-exchange does not have.But traditional single-action and multiple-effect evaporation technology need to provide a large amount of raw steam, and need configure coal firing boiler and cooling system, the energy consumption that is difficult to avoid can be caused and produce a large amount of waste discharges.Cause overall system architecture complicated, bulky, operation and maintenance difficulty, running cost sharply rises simultaneously.
Function of mechanical steam recompression is a kind of evaporation technology, is called for short MVR (Mechanical Vapor Recompression).Refer in evaporation, by secondary steam adiabatic compression, a kind of way that the heating chamber being sent into vaporizer is subsequently reused as thermal source.Secondary steam after compression temperature of saturation raises, and forms enough heat transfer temperature differences, therefore again can be used as termite with boiling liquid in device.Therefore need only supplement a certain amount of compression work, just can utilize a large amount of latent heat of secondary steam.MVR method does not need outside thermal source, and the energy consumption of system is only the energy consumption of compressor and all kinds of pump, so energy-saving effect is quite remarkable.
Also have a large amount of chlorions in seawater, at high temperature can cause serious corrosion to equipment.In addition, the equipment thermosteresis of cold operation is lower, can save a large amount of energy.Therefore, low-temp low-pressure sea water desaltination side has significant advantage.
Low-temperature negative-pressure operation, maintaining vacuum tightness in vaporizer needs to consume electric energy, and supplying water and evaporating rear concentrated seawater discharge also needs to consume a large amount of waste heat.Some patent literatures adopt other method outside electric energy to obtain vacuum environment, as Chinese patent CN101177308A, 201310300526.7 and the CN202880936U method such as seawater gravity and barometric point produce vacuum, required energy Ratios traditional way is few, but these method complex process, equipment volume is huge, also very high to site requirements.Chinese invention patent 201110104604.7,201010300875.5 and 200910138238.X, 200910016942 etc. all provide solar heat compression function of mechanical steam recompression sea water desalinating plant, but the unequal feature of the seasonality of sun power, regionality distribution all becomes the bottleneck that restriction solar seawater desalination is promoted, wherein the waste heat of 201010300875.5,200910016942 pairs of strong brines and product fresh water does not reclaim, and causes the significant wastage of the energy.In addition, these patents have harsh requirement to Working environment, equipment and equipment complexity.Solar heat compression function of mechanical steam recompression sea water desalinating plant is substantially all made up of large number quipments such as solar energy collector, steam injector, compressor, heating chamber, vaporizer, heat exchangers, and complex structure and floor space senior general limit the use of these techniques.The technical scheme of the MVR sea water desalinating plant that patent 20031010755.7 is announced is the equipment comprising steam mechanical vapour compressor, multiple vaporizer and be placed in prolong, sprinkling system etc. in vaporizer, multiple vaporizer realizes multiple-effect stepped evaporation, this technique is equipment and system architecture complexity not only, and the heat dissipation that the outer row reckoning without strong brine and product fresh water causes, be difficult to realize large-scale application and popularize.
Generally speaking, the method utilizing mechanical vapor recompression technology to carry out sea water desaltination in prior art always exists that energy consumption is higher, equipment volume is huge or to the high deficiency of site requirements, and is difficult to realize large-scale application and universal.
Summary of the invention
Technical problem to be solved by this invention overcomes the deficiencies in the prior art, provide that a kind of equipment and process is simple, energy consumption and cost low, function of mechanical steam recompression method for desalting seawater reliably, efficiently and easily.
For overcoming the above problems, the present invention takes following technical scheme:
A kind of efficient mechanical vapor recompression method for desalting seawater, the method adopts function of mechanical steam recompression system to desalinate seawater, and the method comprises:
(1) seawater preheating: charging seawater carries out preheating through seawater preheating device, makes seawater reach evaporation temperature required;
(2) evaporate: the seawater after preheating enters vaporizer, and the pressure in vaporizer is maintained negative pressure, and seawater evaporates in vaporizer, the vaporization of part seawater forms water vapor, and remaining seawater forms strong brine;
(3) vapor recompression: the water vapor that seawater vaporization is formed enters mechanical commprssor and compresses, and the steam that after compression, temperature and pressure improves enters into vaporizer, and after release of heat, condensation forms condensation fresh water in evaporator room;
Particularly:
In step (1), charging seawater is divided into two tunnels, heat exchange is carried out through the first heat exchanger (condensation fresh water heat exchanger) in one tunnel, another road enters the second heat exchanger (strong brine heat exchanger) and carries out heat exchange, thermal source wherein in the first heat exchanger is the condensation fresh water that evaporation produces, the thermal source of the second heat exchanger is the strong brine that evaporation produces, seawater by with condensation fresh water and strong brine heat exchange after reach evaporate temperature required;
Described method for desalting seawater also comprises:
(4) after seawater preheating, carry out degassed to seawater before evaporation, with the room temperature incondensable gas contained by removing in seawater;
(5) part for strong brine evaporation being produced is circulated back in vaporizer, and remainder is passed in the second heat exchanger and carries out heat exchange with charging seawater.
Preferably, in step (2), the working pressure of vaporizer is 9.6KPa ~ 84.5KPa, and vaporization temperature is 45 DEG C-95 DEG C.
Preferably, in step (1), the temperature entering the condensation fresh water of the first heat exchanger is 60 ~ 100 DEG C, and the temperature entering the strong brine of the second heat exchanger is 45 ~ 95 DEG C.
Preferably, in step (1), the seawater through the first heat exchanger is 1:0.8 ~ 1.2 with the throughput ratio through the seawater of the second heat exchanger.
Preferably, at the entrance and exit place of the first heat exchanger and the second heat exchanger, temperature testing equipment is installed.The flow proportional entering the seawater of the first heat exchanger and the second heat exchanger is regulated by adjustable dividing control valve.In reality, the seawater ratio of strong brine heat exchanger and condensation fresh water heat exchanger can be entered according to the temperature of the strong brine and water of condensation that enter heat exchanger and Flow-rate adjustment, improve waste heat recovery effect, simultaneously by the temperature of seawater and strong brine recycle pump coupling control, regulate the circulating brine ratio of strong brine recycle pump according to the temperature of seawater, make seawater reach vaporization temperature.
Preferably, the first heat exchanger and the second heat exchanger all adopt efficient plate-type heat exchanger.
According to the present invention, in step (4), described room temperature incondensable gas comprises oxygen, nitrogen and carbonic acid gas etc.
In step (4), degassed method adopts vacuum type degas method, and the method equipment is simple, and does not use any medicine in process.
Preferably, in step (5), loop back in vaporizer by 5% ~ 30% of the strong brine produced, more preferably, loop back 8% ~ 15% of the strong brine produced in vaporizer.
Preferably, in step (5), will loop back vaporizer strong brine and degassed after sea water mixing after, pass into together in vaporizer.More preferably, by strong brine recycle pump, strong brine is squeezed in seawater feed pipe, and strong brine recycle pump pipeline is communicated with strong brine escape route, carried out the amount of controlled circulation strong brine by the flow controlling strong brine recycle pump.
Preferably, described vaporizer adopts falling-film evaporator, and within it setting pressure test set, water temperature test set and strong brine concentration detection device; Described compressor adopts variable frequency control compressor and is equipped with temperature and pressure test set.More preferably, vaporizer is transverse tube type falling-film evaporator.The vaporizer of the type has the features such as good heat-transfer, evaporation capacity be large.Vaporizer is made up of evaporator room, distribution cavity and recycling cavity, for mutually isolated airtight cavity, condensation tube bank is horizontally disposed is communicated with distribution cavity and recycling cavity in evaporator room, distribution apparatus is positioned at condensation tube bank top, the seawater of spray forms liquid film outward at prolong, and the heat of phase transformation ebuillition of heated discharged by the vapor condensation in pipe forms steam.The steam formed is delivered to compressor via steam outlet pipe, is all improved by the temperature and pressure of the steam after compressing.Steam after compression reenters the condensation in-tube condensation of vaporizer through the steam inlet tube be connected with vaporizer, discharges the seawater outside heat of phase transformation heating tube.Phlegma and freshwater product enrichment in distribution cavity and recycling cavity, then discharged by condensate pump.
Preferably, the pump of vaporizer, compressor, heat exchanger and required use is all connected with PLC control cabinet with control valve group and controlled.
Due to the employing of above technical scheme, the present invention compared with prior art has following advantage:
1, be dissolved with the gas of certain ratio in seawater, these gases, when temperature raises and sea water salinity increases, can be separated out gradually, be mixed in steam.When steam is when evaporator room is as heating medium condensation, these steam can not condensation, the existence of these non-condensable gases can make system condensing pressure raise, very large obstruction is caused to heat transfer process, the inventive method before the evaporation, solution gas in seawater is removed, improves the heat-transfer effect of vaporizer, reduce energy consumption;
2, evaporation is made to carry out under negative pressure, vaporization temperature can be lower, the waste heat of the condensation fresh water and strong brine that reclaim evaporation generation by heat exchanger by seawater preheating to the temperature that can directly evaporate, without the need to carrying out extra heat input to system, can significantly reduce energy consumption;
3, in the present invention, part strong brine is circulated, effectively can maintain the stable of system, also reclaim waste heat efficiently simultaneously, reduced energy consumption.
Generally speaking, the energy consumption of the inventive method can be reduced to traditional function of mechanical steam recompression method for desalting seawater 25% and following, greatly reduce sea water desaltination cost, the present invention simultaneously to equipment and site requirements lower, simple to operate, large-scale application can be realized and popularize.
Accompanying drawing explanation
Below in conjunction with the drawings and specific embodiments, the present invention will be further described in detail:
Fig. 1 is the process flow sheet of method for desalting seawater of the present invention;
Wherein: 1, seawater dividing control valve; 2, strong brine heat exchanger; 3, condensation fresh water heat exchanger; 4, vacuum degassing tower; 5, sea-water pump; 6, vaporizer; 7, Mechanical Vapor Compression; 8, strong brine recycle pump; 9, strong brine overboard pump; 10, strong brine tank; 11, condensate pump; 12, fresh water tank.
Embodiment
See Fig. 1, the invention provides a kind of efficient cryogenic function of mechanical steam recompression method for desalting seawater, its system adopted comprises seawater dividing control valve 1, strong brine heat exchanger 2, condensation fresh water heat exchanger 3, vacuum degassing tower 4, sea-water pump 5, falling-film evaporator 6, Mechanical Vapor Compression 7, strong brine recycle pump 8, strong brine overboard pump 9, strong brine tank 10, condensate pump 11 and the fresh water tank 11 etc. that are connected by pipeline each other.
Charging seawater is heated respectively through after strong brine heat exchanger 2 and condensation fresh water heat exchanger 3 and strong brine and the heat exchange of condensation fresh water, and the seawater after heating enters falling-film evaporator 6 after entering and mixing with the strong brine of strong brine recycle pump 8 after vacuum degassing tower 4 removes room temperature non-condensable gas.
Falling-film evaporator 6 adopts transverse tube type falling-film evaporator, and the vaporizer of the type has good heat-transfer, the evaporation capacity feature such as greatly.Falling-film evaporator 6 is made up of evaporator room, distribution cavity and recycling cavity, for mutually isolated airtight cavity, condensation tube bank is horizontally disposed is communicated with distribution cavity and recycling cavity in evaporator room, distribution apparatus is positioned at condensation tube bank top, the seawater of spray forms liquid film outward at prolong, and the heat of phase transformation ebuillition of heated discharged by the vapor condensation in pipe forms steam.The steam formed is delivered to Mechanical Vapor Compression 7 via steam outlet pipe, is all improved by the temperature and pressure of the steam after compressing.Steam after compression reenters the condensation in-tube condensation of vaporizer through the steam inlet tube be connected with vaporizer, discharges the seawater outside heat of phase transformation heating tube.Phlegma and freshwater product enrichment in distribution cavity and recycling cavity, then discharged by condensate pump 11.
Vaporizer 6 operates under low-temp low-pressure, is provided with pressure, temperature, salinity measurement equipment, is provided with temperature, pressure checking device in Mechanical Vapor Compression 7 in vaporizer 6.Steam mechanical recompression machine 7, vaporizer 6, strong brine recycle pump 8 and relevant control valve group are all connected with PLC housing and controlled, the flow of adjustment strong brine recycle pump 8 and the power of compressor, the pressure and temperature of stable system.
Bottom evaporator room, concentrated solution outlet is set, evaporates the strong brine obtained and discharge through concentrated solution outlet.In order to avoid the impact that extraneous difference variation can be brought to system, in the present invention, part strong brine is circulated, not only reclaimed waste heat more efficiently, also effectively can maintain the stable of system.Strong brine recycle ratio accounts for the 5-30% of strong brine, and preferably 8% ~ 15%.
Strong brine and condensation fresh water heat exchange seawater in strong brine heat exchanger 2, condensation fresh water heat exchanger 3, recovery waste heat, then enters strong brine storage tank 10 and fresh water storage tank 11 respectively.Enter heat exchanger 2, the temperature of the water of condensation of 3 is about 60 ~ 100 DEG C, and the temperature of strong brine is 45 ~ 95 DEG C.Fully reclaimed by waste heat in the present invention, adopt efficient plate-type heat exchanger recovery waste heat, waste-heat recovery device by seawater preheating to the temperature that can directly evaporate, therefore without the need to carrying out extra heat input to system, can effectively reduce energy consumption simultaneously.
At the entrance and exit place of strong brine heat exchanger 2, condensation fresh water heat exchanger 3, temperature testing equipment is installed; Strong brine heat exchanger 2, condensation fresh water heat exchanger 3 and control valve group 1 are all connected with PLC housing and controlled.Control valve group 1 is set to adjustable dividing control valve, for regulating the flow rate ratio entering condensation fresh water heat exchanger 3 and strong brine heat exchanger 2, the seawater ratio of strong brine heat exchanger and condensation fresh water heat exchanger can be entered according to the temperature of the strong brine and water of condensation that enter heat exchanger and Flow-rate adjustment, improve waste heat recovery effect, simultaneously by the temperature of seawater and strong brine recycle pump 8 coupling control, regulate the circulating brine ratio of strong brine recycle pump 8 according to the temperature of seawater, make seawater reach vaporization temperature.
Embodiment
A kind of method for desalting seawater, the water outlet ratio of fresh water is 50%, and the method comprises the following step carried out continuously:
(1), seawater preheating: first the seawater of about 20 DEG C regulates through seawater distribution valve group 1 and enter strong brine heat exchanger 2, the flow rate ratio of water of condensation heat exchanger 3 is 1:1, strong brine heat exchanger 2 and water of condensation heat exchanger 3 pass into the strong brine of temperature about 75 DEG C and the condensation fresh water of temperature about 80 DEG C respectively, pass through heat exchange, the temperature of seawater is increased to about 70 DEG C, whole condensation fresh water that evaporation produces all are sent into condensation fresh water heat exchanger 3 and are carried out heat exchange, 90% of the strong brine that evaporation produces is sent into strong brine heat exchanger 2 and is carried out heat exchange, strong brine after heat exchange is disposed to strong brine tank 10.Condensation freshwater product after heat exchange is delivered to fresh water tank 12;
(2), degassed: the seawater after preheating enters vacuum degassing tower 4, removes solution gas wherein, and these solution gass are the incoagulable gas of room temperature, comprise oxygen, nitrogen, carbonic acid gas etc.;
(3), evaporate, recompression: the seawater after degassed with 10% strong brine mix after enter vaporizer 6, in vaporizer 6, seawater completes spray after distribution apparatus, the seawater of spray to absorb heat outward boiling at prolong, part forms steam, evaporation is carried out under temperature 70 C and pressure 45KPa, it is that the condensation in-tube condensation reentering vaporizer 6 after 57.8KPa again produces condensation fresh water that the steam formed compresses rear raising temperature to 85 DEG C and pressure by compressor 7, and the seawater simultaneously outside heating tube forms steam.
comparative example
A kind of method for desalting seawater, the water outlet ratio of fresh water is 50%, and the method comprises the following step carried out continuously:
(1), seawater preheating: the seawater of about 20 DEG C carries out being preheated to 70 DEG C through the conventional seawater preheating device of Electric heating of taking;
(2), evaporate: seawater enters falling-film evaporator, in falling-film evaporator, evaporation is carried out under temperature 70 C and pressure 45KPa, seawater completes spray after distribution apparatus, the seawater of spray to absorb heat outward boiling at prolong, part forms steam, part forms strong brine, strong brine tank delivered to by strong brine, the steam formed is that the condensation in-tube condensation reentering vaporizer after 57.8KPa again produces condensation fresh water by improving temperature to 85 DEG C and pressure after compressor compresses, condensation fresh water delivers to fresh water tank, and the seawater simultaneously outside heating tube forms steam.Steam can discharge non-condensable gas gradually when condensation, can change the condensing pressure of steam after non-condensable gas adds up, and causes the fluctuation of system temperature.
Produce 100m
3desalination water, needed for embodiment and comparative example method, energy consumption is respectively about 2000kW.h and 8000kW.h.
Above to invention has been detailed description; its object is to allow the personage being familiar with this art can understand content of the present invention and be implemented; can not limit the scope of the invention with this; the equivalence change that all spirit according to the present invention are done or modification, all should be encompassed in protection scope of the present invention.