A kind of urea wastewater that contains reclaims technology
Technical field
The present invention relates to the processing of waste water solution in the chemical production field, relate to contain in the urea production process the dense recovery technology of putting forward of urea wastewater specifically.
Background technology
The resulting urea wastewater that contains generally contains NH in factory that makes urea's urea evaporating concentration process
3, CO
2And 1~3% urea, because its serious contaminative, this waste liquid can not directly be discharged in the environment.NH wherein
3, CO
2Usually can propose dense recovery by desorb, and urea is because its non-volatile difficult recovery.Present treatment process generally adopts hydrolysis and desorption technology, guarantees at a certain temperature that promptly containing urea wastewater has enough residence time in hydrolysis tower, so that it is hydrolyzed to NH
3And CO
2, and then reclaimed by stripping or rectifying and to enter carbamide production system.This hydrolysis and desorption technology is divided Dan Ta and two kinds of flow processs of two towers again usually.
As shown in Figure 1, in same tower, be hydrolyzed in the prior art and desorb contain the urea wastewater purification process: contain urea wastewater self-condensation liquid bath 1 after heat exchanger 2 preheatings, enter in the hydrolysis and desorption tower 4, by steam heating, hydrolysis of urea is NH
3And CO
2And in company with the NH that exists in the former waste liquid
3And CO
2Common desorb, stripping gas is after reflux exchanger 5 condensations, and partial condensation liquid is as trim the top of column, and all the other return carbamide production system, the discharging after heat exchanger 2 and water cooler 3 coolings of the bottom liquid effluent of hydrolysis and desorption tower 4.
What Figure 2 shows that hydrolysis and desorb are carried out respectively in the prior art in two towers contains the urea wastewater purification process: contain urea wastewater self-condensation liquid bath 1 after heat exchanger 2 preheatings, enter in first desorption tower 4 NH in the waste liquid
3And CO
2Most of desorb, stripping gas is after reflux exchanger 5 condensations, and partial condensation liquid is as trim the top of column, and first desorption tower, 4 bottom liquid effluents are gone into hydrolysis tower 6 through heat exchanger 7 heating are laggard, this hydrolysis tower provides hydrolysis institute heat requirement by steam, and hydrolysis of urea is NH in the waste liquid in this tower
3And CO
2, the raffinate after the hydrolysis enters second desorption tower 8 after heat exchanger 7 heat exchange, in this tower steam with raffinate in NH
3And CO
2Desorb removes once more, liquid effluent discharging after heat exchanger 2 and water cooler 3 coolings at the bottom of the tower, and the cat head vent gas is as first desorption tower, 4 heating gas.
Find that by long-term industrial production there is following problem in said hydrolyzed-desorption technique:
1. be abundant hydrolysis, require to contain urea wastewater and in equipment, stops and reach 80~100 minutes, so required equipment be huge that investment is high, as a cover processing liquid measure 5m
3The hydrolysis device of/h need be made an investment in more than 100 ten thousand yuans.
2. for making the urea decomposition that contains in the urea wastewater, need under excessive steam, to operate, thereby must consume a large amount of high temperature and high pressure steams, and then cause high energy consumption and high process cost.
3. that reclaims contains NH
3, CO
2Moisture more in the gas, cause H in the urea after sending Urea Conversion System back to
2O/CO
2Improve, increased the energy consumption of urea synthesis.
The employing that also has in the prior art in addition is only with the NH in the waste liquid
3And CO
2Reclaim the technical process that contains the direct discharging of urea wastewater after the desorb by the desorption tower desorb.Be illustrated in figure 3 as do not have a hydrolysis contain urea wastewater desorption technique flow process: contain urea wastewater self-condensation liquid bath 1 after heat exchanger 2 preheatings, enter desorption tower 4, by steam heating, the NH in the urea wastewater
3And CO
2Desorb, stripping gas is after reflux exchanger 5 condensations, partial condensation liquid is as trim the top of column, all the other return carbamide production system, desorption tower 4 bottom liquid effluents after heat exchanger 2 cooling as discharge of wastewater.Though this technology flow process and equipment are simple, only in desorption tower, reclaimed the NH in the waste liquid by desorb
3And CO
2, and contained urea wastewater directly discharges, and this processing method has not only caused financial loss, and the waste water that exceeds standard has simultaneously caused severe contamination to environment.
Summary of the invention
Contain the above problem that exists in the urea wastewater processing technological flow at existing urea process, low-pressure steam mostly is the characteristics that the middle pressure steam decompression comes in conjunction with the factory that makes urea's low pressure steam purposes that with coal is raw material is more, the invention provides a kind of urea technique and contain the dense recovery technical process of proposing of urea wastewater, be used to solve problems such as high energy consumption, the high process cost of prior art and the discharging that exceeds standard.
The object of the present invention is achieved like this:
At first will contain urea wastewater self-condensation liquid bath 1 after heat exchanger 2 preheatings, send into desorption tower 4, make the NH that contains in the urea wastewater by the steam indirect heating
3And CO
2Desorb;
To contain NH then
3And CO
2Stripping gas through reflux exchanger 5 condensations, phlegma is divided into two-way, the one tunnel as trim the top of column, carbamide production system is returned on another road;
The urea wastewater that contains that desorption tower 4 is discharged is divided into two-way again, desorption tower 4 bottoms are returned in 9 heating of one tunnel process reboiler, vaporizer 10 middle pressure steam evaporation concentration is sent on another road, when being concentrated to urea concentration when being 20~50%, send the urea concentrated solution that obtains back to Urea Evaporation System, the secondary steam that produces in the vaporizer 10 is drawn and is delivered to steam vapour system.
Wherein said middle pressure steam is 500~3.9 * 10
3Kpa, the control evaporating pressure is 200~500Kpa during evaporation, secondary steam pressure is 200~500Kpa, to satisfy the requirement of steam vapour system.
The technical progress that the present invention obtains:
1. facility investment is few, and facility investment only is about 1/3 of a hydrolysis and desorption technology under the same processing power.
2. made full use of the useful energy of middle pressure steam, promptly be issued to the purpose of carrying dense recovery urea in the condition that does not reduce the middle pressure steam utility value substantially.
3. existing containing in the urea wastewater hydrolysis and desorption technology, urea is hydrolyzed into NH
3And CO
2Recovery is entrained with a large amount of water often and enters carbamide production system.And the present invention proposes dense recovery with waste liquid, thereby can not cause water cycle amount raising in the carbamide production system.
4. really realized containing the zero release of urea wastewater, eliminated the pollution of discharging of waste liquid environment.
5. save resource, reduced production cost, improved the business economic benefit.Contain urea wastewater hydrolysis and desorption technology with the urea technique of using always at present and compare, a factory that produces 100000 tons of urea per year can reclaim 400~1200 tons in urea every year more.
Description of drawings
Below in conjunction with drawings and the specific embodiments the present invention is further described:
Fig. 1 is the desorption technique schematic flow sheet that is hydrolyzed in the prior art in same tower.
Wherein 1 represents the condensation liquid bath, and 2 is heat exchanger, and 3 is water cooler, and 4 is the hydrolysis and desorption tower, and 5 is condenser.
Fig. 2 is for being hydrolyzed in two towers respectively in the prior art-process flow diagram of desorb.
Wherein 4 is first desorption tower, and 6 is hydrolysis tower, and 7 is heat exchanger, and 8 is second desorption tower.
Fig. 3 is a prior art desorption technique schematic flow sheet.
Fig. 4 is a process flow diagram of the present invention.
Embodiment
Embodiment 1: as shown in Figure 4, at first urea technique is contained urea, NH
3And CO
2Waste liquid self-condensation liquid bath 1 after heat exchanger 2 preheatings, send into desorption tower 4, make the NH that contains in the urea wastewater by the steam indirect heating
3And CO
2Desorb; To contain NH then
3And CO
2Stripping gas through reflux exchanger 5 condensations, phlegma is divided into two-way, the one tunnel as trim the top of column, carbamide production system is returned on another road; The urea wastewater that desorption tower 4 is discharged is divided into two-way again, desorption tower 4 bottoms are returned in 9 heating of one tunnel process reboiler, vaporizer 10 is sent on another road, be controlled at evaporation concentration under the pressure of 300Kpa with the middle pressure steam of 2000Kpa, when being concentrated to urea concentration when being 40%, send the urea concentrated solution that obtains back to Urea Evaporation System, and the secondary steams that produce in the vaporizer 10 are drawn and are delivered to steam vapour system, to satisfy the requirement of steam vapour system.
Below enumerate other embodiments of the invention, difference from Example 1 sees the following form:
| Middle pressure steam (Kpa) | Secondary steam pressure (Kpa) | Solution urea concentration (%) |
Embodiment 2 | 1000 | 500 | 20 |
Embodiment 3 | 1300 | 300 | 30 |
Embodiment 4 | 3900 | 200 | 50 |