CN1003582B - Separating ammonium of circular gas of synthesis by means of dilution of liquid ammonium - Google Patents

Abstract

The present invention relates to a technology for separating ammonia in synthesis recycle gas, which provides a novel method for separating ammonia. The method uses organic solvent as diluting agents and absorbing agents, ammonia in recycle gas is diluted and absorbed, reversible regeneration is carried out, separation effect can be improved, and the power consumption of synthetic ammonia plants can be lowered. The present invention can be suitable for synthetic ammonia plants with different types, especially for low pressure synthesis systems.

Description

The liquefied ammonia dilution method is separated the ammonia in the synthetic cyclic gas

The present invention relates to the isolation technique of ammonia in the synthetic cyclic gas, in existing technology, cold method is adopted in the separation of ammonia usually in the synthetic cyclic gas, and as at present domestic big, medium and small synthesis ammonia plant all adopts this method.Cold method is divided ammonia, need to consume a large amount of freezing merits, and when pressure process reduced, power consumption improves thereupon, is difficult to adapt to synthesis pressure and reduces and requirements of saving energy.For this reason, developed non-freezing minute ammonia technology, as U.S.Patent 3,354,615 have proposed a kind of washing divides ammonia process, but there is a critical defect in this method, and promptly its dividing potential drop of water as solvent is big, more than 100PPm, synthetic gas has not only seriously been stain in its existence, and the activity that has jeopardized ammonia synthesis catalyst, a series of huge dewatering drying device must be set for this reason make up, but still fail to eliminate the hidden danger that makes catalyst deactivation.China goes back to the Gongxian Guo fertilizer plant and has tried out washing branch ammonia technology, shows that through practice test mainly there are three big shortcomings in this method:

1. though NH ₃Meltage in water is bigger, because the polarity of water is big, and the desorb difficulty, thus divide ammonia efficient to reduce.

2. huge drying installation need be set, not only facility investment is big, and often regeneration of siccative, and energy consumption is big.

3. the easy inactivation of catalyzer, the life-span is shorter.

Therefore, this method is difficult for promoting.

In order to overcome the shortcoming that washing divides ammonia process, people have been developed organic solvent and have been divided the ammonia technology, as the S.U.452.171 patent, propose to adopt adiponitrile, N-N-methyl-2-2-pyrrolidone N-organic solvent is as the absorption agent of ammonia, can effectively ammonia be separated from synthetic cyclic gas, but there is following critical defect in the organic solvent that this patent provided:

1. toxicity is big, as adiponitrile.

2. price is expensive, particularly the N-N-methyl-2-2-pyrrolidone N-.

3. seriously corroded, equipment can not long-term operation.

Therefore, also be difficult to obtain industrial application.

The objective of the invention is to overcome the shortcoming of above-mentioned all methods, provide a class to have organic solvent nontoxic, free from corrosion, inexpensive, that the ammonia meltage is big, volatility is low, as liquefied ammonia thinner and absorption agent, and isolate ammonia in the synthetic cyclic gas efficiently with their effect.

Main points of the present invention are, select a kind of ideal organic solvent as the liquefied ammonia thinner, simultaneously the double as absorption agent; Synthetic cyclic gas at first contacts with absorption agent under the overhead streams in the absorption tower, and cooling continuously; Absorption agent can adopt with ammonia and infinitely dissolve each other, and the organic solvent that vapour pressure is very low, play dual parts dilution and absorption during the course, thereby the content that makes the absorption tower be sent to ammonia in the synthetic gas of subsequent handling can significantly be lower than conventional cold method, and the content of organic solvent can be lower than 1PPm usually in the gas; The rich solution that tower bottom flow goes out by the decompression and (or) heating method, in revivifier, the ammonia in the rich solution is discharged; Regenerative process adopts the renovation process of the reversible adverse current of heating continuously, and the ammonia that discharges under different regeneration pressures can be gas ammonia or liquefied ammonia, and respectively as product, lean solution then recycles by the pumped back absorption tower.

Fig. 1 is the 150kg/cm of this method ²The large-scale ammonia plant process flow sheet.

Fig. 2 is the 300kg/cm of this method ²Medium-sized synthesis ammonia plant process flow sheet.

Fig. 3 is the 200kg/cm of this method ²Small-sized synthesis ammonia plant process flow sheet.

In the flow process of Fig. 1, synthetic cyclic gas is sent into absorption tower (2) and is contacted with absorption agent after replenishing virgin gas, finishes branch ammonia purpose.Synthetic gas behind minute ammonia leaves cat head, by charcoal filter (1), enters synthetic tower behind the removing absorption agent.And rich solution is drawn at the bottom of tower, can be decompressed to 16kg/cm through turbine (3) recovered energy ², behind preheater (5), enter regenerator column (6), heating continuously in tower, lean solution is sent the absorption tower back to by pump (4) pressurization and is recycled after heat recuperation and cooling.The gas ammonia that discharges obtains liquefied ammonia by reflux tower (7) through cooling, sends into liquefied ammonia groove (8).

In the flow process of Fig. 2, its absorption and regeneration flow process partly and large-scale ammonia plant cardinal principle be * mutually, difference is that medium-sized synthesis ammonia plant is provided with steel and washes workshop section, usually return 350 kilograms of/ton NH approximately, gas ammonia, need liquefaction, the method for its liquefaction system is absorbed the gas ammonia of washing from copper in absorption tower (11) by absorption agent, rich solution after the absorption is admitted in the regenerator column (10), and the working pressure in the regenerator column (10) is 16kg/cm ², with 130 ℃～150 ℃ hot water heating, this part hot water also can continue on for regenerator column (6) and make the regeneration thermal source.The gas ammonia that regenerator column (10) comes out is through return channel (9), and the liquefied ammonia groove is sent in the liquefaction of cooling back.Absorption agent send regenerator column (10) through pump (12) and interchanger (5 '), recycles.

The flow process of Fig. 3 and Fig. 1, Fig. 2 is identical substantially, difference is to be provided with 2 regenerator columns (6) (10), in absorption tower (2), absorbed the rich solution regeneration in regenerator column (6) earlier of ammonia, obtain liquefied ammonia, then in further regeneration of regenerator column (10), obtain gas ammonia, liquefied ammonia is sent to copper washing section, gas ammonia is sent to carbonization workshop section, replace turbine with throttling valve (3) simultaneously, and corresponding increase heat-exchange equipment (5 '), (5 ") and reflux (9); because regenerator column (6) adopts phreatic water; the regeneration pressure of regenerator column (10) is low, then distinguishes available hot water below 85 ℃ as thermal source, has opened up approach for carbonization flow process small fertilizer plant makes full use of low-grade heat source.

Key problem in technology of the present invention is to select excellent property, has diluting effect for ammonia, the organic solvent of sorption arranged, as glycerol, polyoxyethylene glycol and derivative thereof again.

Organic solvent provided by the present invention not only has nontoxic, non-corrosiveness and advantage such as cheap and easy to get, and its minute ammonia usefulness than S.U.452, the branch ammonia usefulness of 171 patents increases significantly, as S.U.452,171 patents are at 1 meter ³Solution in, only separablely go out 610HM ³Ammonia, and the present invention is at 1 meter ³Solution in separablely at least go out 940HM ³Ammonia, its minute ammonia usefulness can improve more than 50% at least.

In addition, because organic solvent provided by the invention, its vapour pressure is very low, meets the requirement of desirable organic solvent, and promptly the content of organic solvent is lower than 1PPm in gas.So 1 ton of NH of every production ₃The loss of organic solvent can be reduced to below the 0.1kg.Table 1, table 2, table 3 have been done evaluation to the techno-economic effect that various types of synthesis ammonia plants use method of the present invention to produce respectively, have fully shown industrial prospect of the present invention.

The energy of table 1 Large Scale Synthetic Ammonia Plants and economic evaluation

The liquefied ammonia product, summer temperature

(benchmark: ton NH ₃)

Purify and require: NH ₃=2.1%

Project	Savable amount ＊	Unit price	Income unit
	Conversion thermal energy kcal
				Ice maker	200Kwh 60×10 4	0.054 unit/degree	10.80
Circulator	20Kwh 6×10 4	0.054 unit/degree	1.08
				High-pressure unit	6Kwh 1.8×10 4	0.054 unit/degree	0.32
Subtotal	67.8×10 4		12.20

Project	Need the amount of consumption ＊	Unit price	Expenditure unit
	Amount conversion heat energy kcal
				The regeneration heat supply	38×10 4kcal 34.8×10 4(150→78℃)	9 yuan/1,000,000 kilocalories	3.13
Water coolant	44 4.4×10 4	0.024 unit/ton	1.06
				Pump	4kwh 1.2×10 4	0.054 unit/degree	0.21
Thinner	0.1kg	8.5 unit/kilogram	0.85
				Subtotal	40.4×10 4		5.25
Energy is benefited	27.4×10 4kcal	Economic benefit+6.95 yuan

^*The energy converting standard:

1Kwh＝3000kcal;

1 ton of recirculated water=1000kcal;

Low-grade heat source is pressed 7kg/cm ²The thermo-efficiency of steam is benchmark, converts to standard thermal with thermal efficiency ratio.

The energy and the economic evaluation of the medium-sized ammonia of table 2 factory

The liquefied ammonia product, summer temp

(benchmark: ton NH ₃)

Purify and require: NH ₃=1.5%

Project	Savable amount ＊	Unit price	Income unit
	Conversion thermal energy kcal
				Ice maker	115Kwh 34.5×10 4	0.054 unit/degree	6.21
Circulator	10Kwh 6×10 4	0.054 unit/degree	1.08
				High-pressure unit	6Kwh 1.8×10 4	0.054 unit/degree	0.32

Project	Need the amount of consumption ＊	Unit price	Expenditure unit
	Amount conversion heat energy kcal
				The regenerator column heat supply	30×10 4kcal 28.6×10 4(130→78℃)	9 yuan/1,000,000 kilocalories	2.12
Separate the heat supply of ammonia tower	14×10 4 kcal 11×10 4(150→130℃)	9 yuan/1,000,000 kilocalories	0.99
				Water coolant	50 5×10 4	0.024 unit/ton	1.20
Pump	7kwh 2.1×10 4	0.054 unit/degree	0.38
				Thinner	0.2kg	8.5 unit/kilogram	1.70
Subtotal	4*.7×10 4		6.39
				Energy is benefited	0.6×10 4 kcal	Economic benefit+1.22 yuan

^*The energy conversion is accurate referring to table 1

The table 3 small ammonia (200kg/cm of factory ²) energy and economic evaluation

The gas ammonia product, summer temperature

(benchmark: ton NH ₃)

Purify and require: NH ₃=1.5%

Project	Savable amount ＊	Unit price	Income unit
	Conversion thermal energy kcal
				Ice maker	65Kwh 19.5×10 4	0.054 unit/degree	3.51
Circulator	20Kwh 6×10 4	0.054 unit/degree	1.08
				High-pressure unit	6Kwh 1.8×10 4	0.054 unit/degree	0.32
Subtotal	27.3×10 4		4.91

Project	Need the amount of consumption ＊	Unit price	Expenditure unit
	Amount conversion heat energy kcal
				The #1 heat supply of regenerating	11.3×10 4kcal 50×10 4(35→78℃)	9 yuan/1,000,000 kilocalories	0.45
The #2 heat supply of regenerating	22.8×10 4kcal 8.7×10 4(78→63℃)	9 yuan/1,000,000 kilocalories	0.78
				Water coolant	40 4×10 4	0.024 unit/ton	0.96
Pump	10kwh (comprising phreatic water) 3 * 10 4	0.054 unit/degree	0.54
				Thinner	0.1kg	8.5 unit/kilogram	0.85
Subtotal	20.7×10 4		3.58
				Energy is benefited	6.6×10 4 kcal	Economic benefit+1.33 yuan

^*The energy converting standard is referring to table 1

Comparison shows that by above-mentioned:

1. because organic solvent provided by the present invention, have nontoxic, non-corrosiveness, steam and force down, divide ammonia usefulness height, advantage such as cheap and easy to get, thereby making method of the present invention can replace cold method effectively carries out industrialization, has reached technology and economic unification.

2. various types of synthesis ammonia plants all can adopt method of the present invention, and receive good economical effectiveness.

3. when using organic solvent provided by the present invention to carry out branch ammonia, the pressure when it absorbs operation can be 150～300kg/cm ², but be good with the low pressure synthesis system.

Claims (1)

1, a kind of method of separating ammonia in the synthetic cyclic gas, at first in the absorption tower, organic solvent fully contacts with the synthetic cyclic gas of pressurization, ammonia in dilution and the absorption circulation gas, be sent to regenerator column by the rich solution of discharging at the bottom of the tower, continuous decompression and (or) under the condition of heating regeneration discharge ammonia, through cool off the liquefied ammonia product, lean solution after the regeneration is recycled by the pumped back absorption tower, it is nontoxic to the invention is characterized in that said organic solvent is that a class has, there is not corrosion, steam forces down, divide ammonia usefulness height, the organic solvent of advantage such as cheap and easy to get is as glycerol, polyoxyethylene glycol and derivative thereof.

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