CN101531560B - Method for purifying methane from oxygen-containing coal bed gas by low-temperature liquefaction separation - Google Patents
Method for purifying methane from oxygen-containing coal bed gas by low-temperature liquefaction separation Download PDFInfo
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 420
- 239000007789 gas Substances 0.000 title claims abstract description 177
- 229910052760 oxygen Inorganic materials 0.000 title claims abstract description 140
- 239000001301 oxygen Substances 0.000 title claims abstract description 139
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 title claims abstract description 135
- 238000000034 method Methods 0.000 title claims abstract description 72
- 238000000926 separation method Methods 0.000 title claims abstract description 57
- 239000003245 coal Substances 0.000 title abstract description 15
- 238000004880 explosion Methods 0.000 claims abstract description 68
- 230000008569 process Effects 0.000 claims abstract description 38
- 238000001816 cooling Methods 0.000 claims abstract description 8
- 239000002360 explosive Substances 0.000 claims description 68
- 238000011084 recovery Methods 0.000 claims description 45
- 238000004821 distillation Methods 0.000 claims description 37
- 238000005422 blasting Methods 0.000 claims description 35
- 239000007788 liquid Substances 0.000 claims description 19
- 238000005057 refrigeration Methods 0.000 claims description 15
- 238000000746 purification Methods 0.000 claims description 8
- 238000001514 detection method Methods 0.000 claims description 5
- FFBHFFJDDLITSX-UHFFFAOYSA-N benzyl N-[2-hydroxy-4-(3-oxomorpholin-4-yl)phenyl]carbamate Chemical compound OC1=C(NC(=O)OCC2=CC=CC=C2)C=CC(=C1)N1CCOCC1=O FFBHFFJDDLITSX-UHFFFAOYSA-N 0.000 claims description 2
- 239000002994 raw material Substances 0.000 abstract description 6
- 239000000203 mixture Substances 0.000 description 19
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 17
- 229910052757 nitrogen Inorganic materials 0.000 description 9
- 238000000605 extraction Methods 0.000 description 8
- 238000005516 engineering process Methods 0.000 description 7
- 238000004364 calculation method Methods 0.000 description 5
- 238000009835 boiling Methods 0.000 description 4
- 238000002474 experimental method Methods 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- DOTMOQHOJINYBL-UHFFFAOYSA-N molecular nitrogen;molecular oxygen Chemical compound N#N.O=O DOTMOQHOJINYBL-UHFFFAOYSA-N 0.000 description 4
- JVFDADFMKQKAHW-UHFFFAOYSA-N C.[N] Chemical compound C.[N] JVFDADFMKQKAHW-UHFFFAOYSA-N 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000012528 membrane Substances 0.000 description 3
- 239000012071 phase Substances 0.000 description 3
- 230000000630 rising effect Effects 0.000 description 3
- 238000001179 sorption measurement Methods 0.000 description 3
- 235000009508 confectionery Nutrition 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000005194 fractionation Methods 0.000 description 2
- 239000003345 natural gas Substances 0.000 description 2
- 238000007781 pre-processing Methods 0.000 description 2
- 230000002265 prevention Effects 0.000 description 2
- 238000000638 solvent extraction Methods 0.000 description 2
- 230000032258 transport Effects 0.000 description 2
- NLOAOXIUYAGBGO-UHFFFAOYSA-N C.[O] Chemical compound C.[O] NLOAOXIUYAGBGO-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
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- 230000002631 hypothermal effect Effects 0.000 description 1
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- 238000010297 mechanical methods and process Methods 0.000 description 1
- 230000005226 mechanical processes and functions Effects 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 229910052756 noble gas Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- -1 polyoxy Polymers 0.000 description 1
- 238000002203 pretreatment Methods 0.000 description 1
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Abstract
The invention provides a method for separating and purifying methane from oxygen-containing coal bed gas, which comprises the steps of firstly cooling raw material gas of the oxygen-containing coal bed gas, and then rectifying the oxygen-containing coal bed gas to obtain the separated and purified methane, wherein a) the volume concentration Y of the methane is used as a horizontal coordinate, and the volume concentration X of the oxygen is used as a vertical coordinate, and the horizontal coordinate is used for establishing an explosion triangle aiming at a position where the explosion is most likely to occur in a separation process flow; b) detecting the initial volume concentration Y of methane in the feed gas0(ii) a c) When Y is0Greater than the upper explosion limit point Y of the explosion triangle11.0-1.1 times of the temperature, increasing the refrigerating capacity or reducing the flow of the raw material gas, thereby reducing the temperature at the position; d) repeating steps b) to c) until Y0Is Y11.0-1.1 times of the total temperature of the oxygen-containing coal bed gas, wherein the temperature at the current position is the lowest safe separation temperature, and the methane can be safely separated and purified from the oxygen-containing coal bed gas by maintaining the temperature to be 0-5 ℃ above the lowest safe separation temperature. The method provided by the invention reduces the pretreatment process and pretreatment equipment of the raw material gas, thereby greatly reducing the cost.
Description
Technical field
The present invention relates to separate with low-temperature liquefaction the method for purification methane from coalbed methane containing oxygen, belong to mixed gas separating and purifying technology field.
Background technology
Coal-seam gas belongs to unconventional Sweet natural gas, namely coal form and evolutionary process in generate, through migrating, being present in Sweet natural gas in the coal seam with adsorbed state.The major ingredient of coal-seam gas is methane, is the energy of a kind of cleaning and high heating value.China's coal bed gas resource is very abundant, and basic reserves are suitable with conventional gas.Coal-seam gas has two kinds of extraction ways: a kind of is ground extraction, and methane purity is high in its coal-seam gas, can reach about 98%.This gas utilization value ratio is higher, can direct weighting carries out pipe network and transports the accumulating of also can directly liquefying.But the coal-seam gas extraction way is extraction under the mine that carries out coal mining production more widely.Methane content is lower in the middle of this mode extraction coal-seam gas out, usually between 30%～70%.Within one quite long period, in the middle of the China's coal-mine recovery process, rely on extraction under the mine always, the extraction of coal-seam gas (being commonly referred to coal mine gas) is processed the requirement that only is in Safety of Coal Mine Production and is carried out.
The separating-purifying methane gas is significant for effective rate of utilization and the economic worth of expansion and raising coal-seam gas from mine coal seam gas.China's coal-seam gas has enormous amount, and the place of production disperses, the individual well small scale, and down-hole extraction gas concentration is low and contain the characteristics such as oxygen, must have safety, economic separation storaging and transport technology fully rationally to utilize.
The method that can be applied at present separating-purifying methane from coal-seam gas generally has the schemes such as low-temperature liquefaction separation, pressure-variable adsorption and membrane sepn, and every kind of technical scheme all has the characteristic of oneself and has separately range of application.But when containing the flammable coalbed methane containing oxygen of oxygen for the similar mine coal seam gas of separating treatment is this, safety problem becomes the problem that all isolation technique must be considered.Methane is a kind of inflammable gas, has an explosion ratio scope with air mixed, is 5%～15% at normal temperatures and pressures.This concentration range can change along with the variation of pressure and temperature, and wherein temperature rising and pressure raise and all can make the explosion ratio range extension.From mine coal seam gas, be separating-purifying methane in the coalbed methane containing oxygen of air and methane, no matter in the initial coalbed methane containing oxygen methane concentration have how high, along with the separation of methane reduces, all can pass the explosion ratio scope in system, this all is breakneck for any system for separating and purifying.
At present, the various gas separations such as low-temperature liquefaction separation, pressure-variable adsorption and membrane sepn are applied to the technology report of purification methane from coal-seam gas comparatively rare.Wherein Chinese patent application 200610080889.4,200610103425.0 discloses a kind of technical process that liquefaction separates for coalbed methane containing oxygen, adopt low temperature fractionation and fractionation measure can realize the methane of from coalbed methane containing oxygen, purifying, and can obtain the nitrogen of higher degree, can add in the middle of the cold recovery system.Yet in actual mechanical process, because in the process of purifying, the concentration of methane constantly reduces, the concentration of oxygen constantly raises, may exist the temperature of coalbed methane containing oxygen to reach the detonation point of methane, this just may cause the blast of mixed gas, this patent application is not specifically related to how to solve the technical scheme of safety problem, and flow process will further be separated nitrogen processed to containing methane tail gas, liquid-air, oxygen-rich liquid and gaseous oxygen can appear in system, there is more danger, also this do not proposed solution.Chinese patent application 200410040155.4 also discloses a kind of scheme that adopts low-temperature liquefaction to separate coal-seam gas purification methane, has wherein mentioned and will carry out just can carrying out the low-temperature liquefaction separation after the degree of depth deoxidation treatment to the raw material coal-seam gas.For the pressure-variable adsorption that adopts in the separating technology and membrane separation process, in separation process scheme, need unstripped gas is pressurizeed, this has significantly enlarged the explosion ratio scope of coal-seam gas, and it is necessary therefore taking deoxidation or other security measuress.The technique means present for deoxidation in the coal-seam gas has: the methods such as catalyzed oxidation and chemical industry conversion, but degree of depth deoxidation has the high or problem such as Technical Economy is bad, technology maturity is inadequate of cost, to containing in the coal-seam gas than polyoxy, low concentration coal-bed gas is not yet seen plant-scale application example.
According to Theory of Combustion, there is the oxygen concn that fires of a minimum in the inflammable gas-oxygen such as methane-noble gas mixtures, the point of its correspondence is called and fires stagnation point, the blast upper and lower limit concentration point of itself and inflammable gas-oxygen mixture has consisted of a trilateral, only have the coalbed methane containing oxygen concentration range of working as to be in this explosion triangle, system just might blast." coal-mine gas diaster prevention and control and utilize technical manual " 2005 the 120th page, the coordinates regional of methane air mixed gas of Fig. 1 and the schematic diagram of the explosion triangle in this coordinates regional are disclosed, this figure is commonly referred to the Coward trilateral, among the figure whole concentration range is divided into I, II, III and four zones of IV.In the realization, the division in these four zones and coalbed methane containing oxygen concentration, pressure and temperature all have relation.Further specify in conjunction with Fig. 2 and the typical mixed gas low ternperature separation process of Fig. 3 flow process.Unstripped gas enters at first that the cold recovery system progressively lowers the temperature until the part component becomes liquid, enters distillation system, obtains liquid straight product, top discharge tail gas in the distillation system bottom.Liquid straight product is directly exported with gaseous state with low temperature liquid or after returning cold recovery system recoveries cold.Also rectifying tower can be separated into a gas-liquid separator and a gas stripping column in this flow process, see Fig. 4.
The characteristics of low ternperature separation process are: by suitable flow process, can realize that high boiling separated component gradually reduces continuously in the gaseous state material, change the liquid state that contains the lower boiling composition into, more the total amount of lower boiling component is then substantially constant.During the II district of the coordinates regional that the temperature, pressure of position of the most easily blasting in feed(raw material)inlet component concentration is in system determined, the deep hypothermia sepn process always will be passed through the I district.The component concentration of the output object of having a few in the Cryogenic Separating Process (liquid and gas) can accurately be obtained in conjunction with the material balance method by Phase Equilibrium Calculation by component and concentration, the local pressure and temperature of coalbed methane containing oxygen.When separated component differed larger with residue component boiling point, after system pressure was determined, the gas phase component concentration of any position can only be determined by local temperature comparatively exactly in the system.The core concept of utilizing the These characteristics of low ternperature separation process to form technical solution of the present invention is: by unstripped gas CONCENTRATION STATE point being judged and control is liquefied and separated minimum temperature the concentration of methane in the gas phase of having a few in the sepn process all is controlled at explosion triangle, that is: beyond the I district.
Summary of the invention
Therefore, the purpose of this invention is to provide a kind of from coalbed methane containing oxygen the method for safe purifying and separating methane.
" separation system " hereinafter comprises refrigeration, distillation system or adds on this basis the cold recovery system and the system of the formation of the connecting tube between them.
The invention provides a kind of method with low-temperature liquefaction separation method safe purification methane from coalbed methane containing oxygen, the method may further comprise the steps: at first the unstripped gas of coalbed methane containing oxygen is lowered the temperature, then described coalbed methane containing oxygen is carried out rectification process, namely get the methane through separating-purifying, wherein
A) take the volumetric concentration Y of methane as X-coordinate, the volumetric concentration X of oxygen is ordinate zou, is used for setting up the coordinates regional for the coalbed methane containing oxygen of separation process scheme, and determines the explosion triangle of the position of the most easily blasting in this technical process;
B) the original volume concentration Y of the methane in the detection unstripped gas
0
C) work as Y
0Upper explosive limit point Y greater than explosion triangle
11.0～1.1 times the time, increase refrigerating duty, perhaps reduce raw gas flow, thereby reduce the temperature of this position;
D) repeating step is a) to c), until Y
0Be Y
11.0～1.1 times, the temperature of current this position is the safe separating minimum temperature, keeps the above 0-5 of this temperature ℃ of safely separating-purifying methane from coalbed methane containing oxygen.
Preferably, the explosion triangle of described coalbed methane containing oxygen is set up by the following method:
A) the volumetric concentration Y with methane is defined as the coordinate transverse axis, and the volumetric concentration X of oxygen is defined as the coordinate longitudinal axis, and the intersection point O (0,0) of two coordinate axis is true origin, and the volumetric concentration of methane is 100%, and the oxysome volume concentrations is that 0 point is defined as the B point;
B) straight-line equation of the mixed gas of methane and air in rectification process
With the intersection point of the coordinate longitudinal axis be A
1, tie point A
1, B forms the mixed gas straight-line equation A of methane and air
1B, X
O2The volumetric concentration of expression oxygen, Y represents the volumetric concentration of methane;
C) Lower Explosive Limit point L, the upper explosive limit point V with the mixed gas of methane under the normal temperature and pressure and air is connected with critical explosion concentration point N, the explosion triangle LVN that forms coalbed methane containing oxygen under the normal temperature and pressure, LN is the Lower Explosive Limit line of coalbed methane containing oxygen under the normal temperature and pressure, and VN is the upper explosive limit line of coalbed methane containing oxygen under the normal temperature and pressure;
D) by under non-normal temperature and pressure, the Lower Explosive Limit point L of the mixed gas of methane and air under the temperature and pressure of the position of the most easily blasting in the technical process
1, upper explosive limit point V
1Make respectively the parallel lines of LN and VN, two parallel lines intersect at N
0Point, then trilateral L
1V
1N
0Be the explosion triangle of the coalbed methane containing oxygen under this temperature and pressure condition, L
1N
0Be the Lower Explosive Limit line of coalbed methane containing oxygen under this temperature and pressure condition, V
1N
0Upper explosive limit line for coalbed methane containing oxygen under this temperature and pressure condition;
E) the volumetric concentration Y of the methane in the coalbed methane containing oxygen of detection beginning rectification process
cVolumetric concentration X with oxygen
c, will put B (100,0) and some C (Y
c, X
c) connect, making the straight-line equation BC of coalbed methane containing oxygen, BC and the coordinate longitudinal axis intersect at A
0The point;
F) connect A
0Point, true origin O (0,0) and B point obtain the coordinates regional A of the coalbed methane containing oxygen in the described separation process scheme
0OB;
G) BC and L
1N
0Or its extended line intersects at L
0, with V
1N
0Or its extended line intersects at V
0, tie point L
0, V
0And N
0, the explosion triangle L of the position that obtains the most easily blasting in the described technical process
0V
0N
0
Preferably, described methane is to separate by the following method to obtain from coalbed methane containing oxygen: the unstripped gas of coalbed methane containing oxygen at first enters the refrigeration system cooling, following described coalbed methane containing oxygen enters distillation system and carries out rectification process, flow out tail gas from the distillation system top, pure methane flows out from the distillation system bottom.
The position of preferably, the most easily blasting in the described separation process scheme is the position (1 ') of distillation system outlet.
Owing to when concentration of methane gas observed value in the tail gas that the outlet position of distillation system is located during less than the upper explosive limit point of this position, just may blast, so when initial liquefaction, should improve the tail gas temperature out as far as possible; Increase again in the refrigerator power process, also want progressive action, in order to avoid enter blast area.According to known technology, when unstripped gas starting point concentration point is arranged in the III district of coordinates regional or IV district, can realize directly that the degree of depth of coalbed methane containing oxygen safety is separated.Above-mentioned technical scheme is further represented by the separation process of Fig. 5.
Preferably, the described tail gas that flows out from the distillation system top enters described cold recovery system recoveries cold, flows out from the outlet of cold recovery system again.
Preferably, the position of the most easily blasting in the separation process scheme is preferably the tail gas exit (1 ') at distillation system top and the position between the cold recovery system outlet place (2 ').
Preferably, described cold recovery system is throttling set or expansion gear.
Preferably, described distillation system is rectifying tower.
Preferably, described distillation system is comprised of gas-liquid separator and gas stripping column.
Preferably, described refrigeration system and described cold recovery system are in same device.
In technique scheme when unstripped gas starting point concentration point is in II district outside the explosion triangle, at first according to the low-temperature liquefaction flow process, determine the position of the most easily blasting in the flow process, then in conjunction with the temperature and pressure value of the position of the most easily blasting, that calculates the position of the most easily blasting contains oxygen combustiblematerials explosion triangle higher limit Y
1, for the separation system of not carrying out the tail gas cold recovery, this higher limit is the combustiblematerials upper limit of concentration value corresponding to tail gas outlet (1 ') position at rectifying tower top.And with current tail gas combustiblematerials concentration measurement Y
0Compare.As tail gas combustiblematerials concentration measurement Y
0Greater than upper limit calculated value Y
1The time, then can suitably increase refrigerator power, reduce the tail gas temperature out.Then again calculate low-temperature liquefaction with the temperature of new explosive position and force value and separate tail gas exit higher limit, again compare with observed value, until observed value is when being 1.0～1.1 times of calculated value, then current temperature out is minimum tail gas safe temperature out, keep this safe separating-purifying methane from coalbed methane containing oxygen more than temperature, this technical scheme is seen Fig. 6.
For will carry out the tail gas cold recovery time, because upper explosive limit raises with the rising of temperature, pressure, the most easily blast the position usually in the tail gas outlet position (1 ') at distillation system top and the position between the cold recovery system outlet position (2 '), take this CONCENTRATION STATE point as safety criterion, then guarantee being operated in outside the explosion triangle of whole system.
No matter adopt throttling set or decompressor in the step-down process of tail gas in the cold recovery system, all can calculate by this paper method.All the observed value of local temperature, pressure and the concentration of each point, calculated value are the regulation and control foundation in the low-temperature liquefaction separating system.
The present inventor is surprised to find, and the blast upper limit value and lower limit value of the explosion triangle of coalbed methane containing oxygen is most important to enforcement of the present invention, and the explosion triangle of coalbed methane containing oxygen is subjected to the impact of the factors such as component, temperature and pressure.In conjunction with the document measured data, the application has provided the method for calculation of the explosion triangle of coalbed methane containing oxygen under the normal temperature and pressure, further explains in conjunction with Fig. 7.
(A) under the normal temperature and pressure conditions
On this figure, at first under normal temperature and pressure conditions, methane-oxygen-nitrogen explosion triangle figure as shown in Figure 7.
The concentration coordinate point of mixture in distillation system that forms for known methane gas and air (nitrogen oxygen mixture) is positioned at straight line and 1. goes up, and this straight-line equation is Y=-4.785X
O2+ 100.Y represents the volumetric concentration of the methane in the mixed gas, X
O2O in the expression mixed gas
2Volumetric concentration.Under the normal temperature and pressure conditions, the Lower Explosive Limit point L (5.0,19.88) of the mixture that methane gas and air form, upper explosive limit point V (15.0,17.79), critical explosion concentration point N (5.18,9.47).Under the normal temperature and pressure conditions, the explosion triangle of the mixture of methane gas and air is LNV, and LN is the Lower Explosive Limit line of the mixed gas of methane and air under the normal temperature and pressure, and VN is the upper explosive limit line of the mixed gas of methane and air under the normal temperature and pressure.See " coal-mine gas diaster prevention and control and utilize technical manual " 2005 the 120th page.
Owing to there being following relation in this gas:
Wherein Y represents the volumetric concentration of the methane in the mixture, Y
N2Represent the N in this gas
2Volumetric concentration, X
O2Represent the O in this gas
2Volumetric concentration.Because airborne N
2And O
2Between known proportionlity, can obtain as shown in the formula in oxygen different content X
O2Under coalbed methane containing oxygen, that is: the relational expression of the Lower Explosive Limit line of the mixed gas that forms of the methane of arbitrary proportion, nitrogen and oxygen:
L’LN：
Oxygen different content (X among the figure
O2) under the relational expression of upper explosive limit line of coalbed methane containing oxygen as follows:
V’VN：
Y in formula (1) and the formula (2) also represents the volumetric concentration of the methane in the coalbed methane containing oxygen, X
O2Also represent the O in the coalbed methane containing oxygen
2Volumetric concentration.
(B) under differing temps and the pressure, the present inventor has provided the coordinates regional of mixed gas and the method for calculation of explosion triangle through repeatedly research, further explains in conjunction with Fig. 8.Under differing temps and the pressure condition, the coordinates regional of mixed gas and explosion triangle can be subject to the impact of coalbed methane containing oxygen mixture pressure and temperature.At a certain temperature, the higher explosion triangle area of pressure is larger; Under certain pressure, the lower explosion triangle area of temperature is less.Explosion triangle is determined by the line of 3 of upper explosive limit point, Lower Explosive Limit point and critical explosion concentration point approx.
Following formula (3) is the Lower Explosive Limit equation of coalbed methane containing oxygen mixed gas, and following formula (4) is the upper explosive limit equation of mixed gas.Can find out from following formula (3), the impact that substantially is not stressed of the Lower Explosive Limit of mixed gas is subject to the impact of temperature.Can find out from following formula (4), the upper explosive limit of mixed gas is subjected to pressure and temperature effect simultaneously.Lower Explosive Limit and the upper limit for the mixed gas of methane nitrogen and oxygen under differing temps and the pressure can be calculated by formula (3) and formula (4) respectively:
Y(vol％)＝5.0-0.0042(t-t
0) (3)
Wherein:
V
p0＝0.325exp(0.23P/P
0)+15.35
c＝-0.104exp(-0.313P/P
0)+0.16
P
0＝0.1MPa，t
0＝25℃
Y in the formula (3) represents the methane volumetric concentration in the mixed gas of Lower Explosive Limit, and the Y in the formula (4) represents the methane volumetric concentration in the mixed gas of upper explosive limit.T represents the temperature of this gas, and P represents the pressure of this gas.V
P0, c is intermediate parameters.
Because the concentration coordinate point when the coalbed methane containing oxygen mixture that methane gas and air (nitrogen oxygen mixture) form carries out rectification process in distillation system is positioned at straight line and 1. goes up: Y=-4.785X
O2+ 100, for the position of the most easily blasting under the non-normal temperature and pressure in the separation system, can by temperature, formula (3) and the straight line equation 1. of this position, draw the Lower Explosive Limit point L of this position of the most easily blasting
1, by temperature, pressure, formula (4) and the straight line equation 1. of this point, draw the upper explosive limit point V of this position of the most easily blasting again
1The present application people finds methane gas under differing temps and the pressure and Lower Explosive Limit line and the methane gas of upper explosive limit line parallel under normal temperature and pressure and Lower Explosive Limit line and the upper explosive limit line of air (nitrogen oxygen mixture) of air (nitrogen oxygen mixture), passes through respectively L
1And V
1Point is made the parallel lines of L ' LN and V ' VN, the intersection point N of two parallel lines
0Be critical explosion concentration, will put L
1, V
1And N
0Be connected, obtain the explosion triangle L of the coalbed methane containing oxygen that methane gas under this temperature and pressure and air form
1V
1N
0L
1N
0Be the Lower Explosive Limit line of the mixed gas of methane and air under this temperature and pressure condition, V
1N
0Upper explosive limit line for the mixed gas of methane and air under this temperature and pressure condition.In addition, for the Lower Explosive Limit point L of the position of the most easily blasting under the non-normal temperature and pressure
1, upper explosive limit point V
1Also can obtain by explosion limits experiment, experimental technique can be with reference to the explosion test of the mixed gas of methane well known in the art and air.
In the methods of the invention, the judgement of position of the most easily blasting in the cryogenic separation system is also relevant with the employing idiographic flow, judges with separation system maximum working pressure and maximum operating temperature and calculates the always safety of position of the most easily blasting for any low ternperature separation process flow process.In this separation system, for the separation system that does not have the cold recovery system, the position of the most easily blasting is the tail gas outlet position place at distillation system top, in order to obtain this position upper explosive limit point and Lower Explosive Limit point, and the most easily the blast temperature and pressure of position of needs detection; For the separation system that the cold recovery system is arranged, the position of the most easily blasting is the place, tail gas outlet position at distillation system top and the optional position between the cold recovery system outlet position.
For any one coalbed methane containing oxygen, the mixed gas that forms such as arbitrary proportion methane, oxygen and nitrogen namely, the methane volumetric concentration Y of the mixed gas by detecting the beginning rectification process
CWith oxysome volume concentrations X
CWith the some C (X in the system of coordinates
C, Y
C) be connected with coordinate point B (100,0), can obtain the straight-line equation BC of this coalbed methane containing oxygen, BC and the coordinate longitudinal axis intersect at A
0Point, tie point A
0, O, B form the coordinates regional A of the coalbed methane containing oxygen in the separation process scheme
0OB; BC and L
1N
0Or its extended line intersects at L
0, and BC and V
1N
0Or its extended line intersects at V
0Tie point L
0, V
0, N
0Form explosion triangle L
0V
0N
0
Composition and its top pressure and top temperature in cryogenic separation system take the raw material coalbed methane containing oxygen are determined the coordinates regional of coalbed methane containing oxygen as basis, and divide thus I, II, III and four zones of IV.See Fig. 7, Fig. 8.When unstripped gas starting point concentration point is in III district outside the explosion triangle and IV district, can realize safely directly that then the degree of depth of methane separates, only need control cold recovery cooling system ability this moment or regulate raw gas flow and the separation system minimum temperature is in occur in the separation process more than the oxygen enrichment liquid phase.When unstripped gas starting point concentration point is in II district outside the explosion triangle, i.e. oxygen debt district, methane starting point concentration in this zone Raw gas is greater than the upper explosive limit point Y of explosion triangle
11.0～1.1 times, this moment is then when regulating cold recovery cooling system temperature and refrigerating duty or raw gas flow and make the concentration of the methane concentration lowest part in the coalbed methane containing oxygen in the system be 1.0-1.1 times of methane concentration value of sepn process line and this explosion triangle upper limit line joining, current this temperature is the safe separating minimum temperature, keeps this safe separating-purifying methane from coalbed methane containing oxygen more than temperature.
Use method provided by the invention can realize not needing unstripped gas is done the deoxidation pre-treatment, just can guarantee that coalbed methane containing oxygen can not blast in the low-temperature liquefaction sepn process, reduce feed gas preprocessing technique and pre-processing device, thereby greatly reduced cost.
Description of drawings
Below, describe by reference to the accompanying drawings embodiments of the invention in detail, wherein:
Fig. 1 represents the schematic diagram of explosion triangle.
Fig. 2 represents the separation system of emission-free cold recovery, and device 1 wherein only comprises refrigeration system.
Fig. 3 represents to have the separation system of tail gas cold recovery, and device 1 wherein comprises refrigeration system and cold recovery system.
Fig. 4 represents that distillation system is the separation system of gas-liquid separator and gas stripping column.
Fig. 5 represents the schema of safe purification methane.
Fig. 6 represents the schema without the safe purification methane of cold recovery.
Fig. 7 represents coordinates regional and the explosion triangle of the mixed gas of methane and air under differing temps and the pressure.
Fig. 8 represents coordinates regional and the explosion triangle of coalbed methane containing oxygen under differing temps and the pressure.
Embodiment
A kind of coalbed methane containing oxygen mixture, described coalbed methane containing oxygen is the refrigeration system cooling of access to plant 1 at first, then enter rectifying tower 2 and be separated into tail gas and liquid pure methane, from tail gas exit point 1 ' the outflow tail gas at rectifying tower top, liquid pure methane flows out from rectifier bottoms.
At first determine the most explosive position in the separation system, because this separation system is without cold recovery, separation system is seen Fig. 2.For the separation system without cold recovery, the temperature of coalbed methane containing oxygen in rectifying tower reduces gradually, and the content of methane reduces gradually, the content of oxygen raises gradually, temperature is minimum in the tail gas exit at rectifying tower top, and the content of methane herein reaches minimum, and the content of oxygen reaches the highest.Referring to Fig. 8, the content of methane reaches minimum, and the coordinate point that the content of oxygen reaches the highest position is the most near explosion triangle L in the coordinates regional
0V
0N
0Upper explosive limit point V
0So the position of the most easily blasting is in the position of the tail gas exit point 1 ' at rectifying tower 2 tops.
The original state of this position is temperature-50 ℃, pressure 0.3MPa.Computation process is as follows: take the volumetric concentration Y of methane as X-coordinate, the volumetric concentration X of oxygen is ordinate zou, by the volumetric concentration Y of the methane in the coalbed methane containing oxygen that detects the beginning rectification process
cVolumetric concentration X with oxygen
c, determine the some C (Y in system of coordinates
c, X
c), will put B (100,0) and some C (Y
c, X
c) connect, making the straight-line equation BC of coalbed methane containing oxygen, BC and the coordinate longitudinal axis intersect at A
0The point.Connect A
0Point, true origin O (0,0) and B point obtain the coordinates regional A of the coalbed methane containing oxygen in the described separation process scheme
0OB.
The temperature and pressure at the known place that the most easily blasts obtains Lower Explosive Limit point L at the mixed gas of the methane of the position of the most easily blasting and air by formula (3) and formula (4) and straight line equation 1.
1With upper explosive limit point V
1, these 2 also can record by the explosion limits experiment.Cross some L
1, the some V
1Make respectively the parallel lines of the upper explosive limit line VN of the mixed gas of methane and air under the Lower Explosive Limit line LN of the mixed gas of methane and air under the normal temperature and pressure and the normal temperature and pressure, two parallel lines intersect at N
0Point, i.e. threshold concentration point.
Straight-line equation BC and the L of the coalbed methane containing oxygen of the methane-nitrogen of this separating technology-oxygen
1N
0Extended line intersect at L
0, with V
1N
0Extended line intersect at V
0, tie point L
0, V
0And N
0, obtain the position of the most easily blasting in the separation process scheme, that is: the explosion triangle L of the position of the tail gas exit point 1 ' at rectifying tower 2 tops
0V
0N
0, L
0For the Lower Explosive Limit point of the coalbed methane containing oxygen of the position of the most easily blasting, with V
1N
0Extended line intersect at V
0, V
0For the upper explosive limit point of the coalbed methane containing oxygen of the position of the most easily blasting, at V
0The combustiblematerials concentration 29.5% that the place is corresponding.
Because the starting point concentration of the coalbed methane containing oxygen material gas mixture of methane, oxygen and nitrogen is respectively 70%, 10% and 20%, Y
0=70% upper explosive limit point Y greater than explosion triangle
1=29.5% 1.0～1.1 times, so add the refrigeration work consumption of bigger device 1, the tail gas temperature out is further reduced.Again with new tail gas temperature out and calculation of pressure V
0, V
0The combustiblematerials concentration Y that the place is corresponding
1Again with observed value Y
0Relatively, repeatedly, until tail gas combustiblematerials measurement of concetration is when being 1.0-1.1 times of calculated value, then corresponding tail gas temperature out is minimum tail gas safe temperature out, keep above 5 ℃ of this temperature or this temperature, safe separating-purifying methane from coalbed methane containing oxygen in preferred 3 ℃ of scopes.
A kind of coalbed methane containing oxygen mixture, described coalbed methane containing oxygen is at first lowered the temperature in the refrigeration system of access to plant 1, then enter rectifying tower 2 and be separated into tail gas and liquid pure methane, liquid pure methane flows out from rectifier bottoms, tail gas enters in the cold recovery system of described device 1 and reclaims cold, flow out from the outlet 2 ' of cold recovery system, the refrigeration system in the present embodiment and cold recovery system are all in device 1 again.
At first determine the most explosive position in the separation system, because this separation system has cold recovery, separation system is seen Fig. 3, for the separation system that cold recovery is arranged, do not blast in tail gas exit at the rectifying tower top, the temperature and pressure of the coalbed methane containing oxygen of the position between cold recovery and rectifying tower raises to some extent respectively with respect to the tail gas exit temperature and pressure at rectifying tower top and reduces, the area of temperature rising explosion triangle increases, the pressure decreased explosion triangle is dwindled, and the area increase of concrete explosion triangle is still dwindled by temperature and pressure between cold recovery and the rectifying tower and jointly determined.
So the position of the most easily blasting is in the tail gas exit 1 ' at distillation system top and the position between the cold recovery system outlet place 2 ', further, this position is that the pressure between cold recovery and the rectifying tower remains unchanged substantially, and the position that temperature is the highest is the position of the most easily blasting in the separation system.The original state of this position is temperature-30 ℃, pressure 0.15MPa, and computation process is as follows:
Take the volumetric concentration Y of methane as X-coordinate, the volumetric concentration X of oxygen is ordinate zou, the volumetric concentration Y of the methane by the beginning rectification process
cVolumetric concentration X with oxygen
c, determine the some C (Y in system of coordinates
c, X
c), will put B (100,0) and some C (Y
c, X
c) connect, making the straight-line equation BC of this coalbed methane containing oxygen, BC and the coordinate longitudinal axis intersect at A
0The point.Connect A
0Point, true origin O (0,0) and B point obtain the coordinates regional A of the coalbed methane containing oxygen of described separation system
0OB;
The temperature and pressure at the known place that the most easily blasts obtains Lower Explosive Limit point L at the mixed gas of the methane of the position of the most easily blasting and air by formula (3) and formula (4)
1With upper explosive limit point V
1, these 2 also can record by the explosion limits experiment.Cross some L
1, the some V
1Make respectively the parallel lines of the upper explosive limit line VN of the mixed gas of methane and air under the Lower Explosive Limit line LN of the mixed gas of methane and air under the normal temperature and pressure and the normal temperature and pressure, two parallel lines intersect at N
0Point, i.e. threshold concentration point.
Straight-line equation BC and the L of the coalbed methane containing oxygen of the methane-nitrogen of this separation system-oxygen
1N
0Extended line intersect at L
0, with V
1N
0Extended line intersect at V
0, tie point L
0, V
0And N
0, obtain the explosion triangle L of this position
0V
0N
0, L
0For the Lower Explosive Limit point of the coalbed methane containing oxygen of the position of the most easily blasting, with V
1N
0Extended line intersect at V
0, V
0For the upper explosive limit point of the coalbed methane containing oxygen of the position of the most easily blasting, at V
0The combustiblematerials concentration 14.96% that the place is corresponding.
Because the starting point concentration of methane, oxygen and nitrogen is respectively 80%, 4% and 16%, the low ternperature separation process flow process has the tail gas cold recovery, supposes that the complete outlet original state of tail gas recycle is temperature-30 ℃, pressure 0.15MPa.Y
0=80% upper explosive limit point Y greater than explosion triangle
1=14.96% 1.0～1.1 times, so add the refrigeration work consumption of bigger device 1 refrigeration system, the tail gas temperature out is further reduced.Again with new tail gas temperature out and calculation of pressure V
0, V
0The combustiblematerials concentration Y that the place is corresponding
1Again with observed value Y
0Relatively, repeatedly, until tail gas combustiblematerials measurement of concetration is when being 1.0-1.1 times of calculated value, then corresponding tail gas temperature out is minimum tail gas safe temperature out, keeps in the above 2 ℃ of scopes of this temperature or this temperature safely separating-purifying methane from coalbed methane containing oxygen.
Embodiment 3
A kind of coal-seam gas oxygen-containing mixture, the at first cooling of the refrigeration system in the access to plant 1 of described coalbed methane containing oxygen, then enter distillation system 2 and be separated into tail gas and liquid pure methane, liquid pure methane flows out from the distillation system bottom, and tail gas flows out from the top 1 ' of distillation system 2.
Because this separation system is without cold recovery, thus the position of the most easily blasting in the position of the tail gas exit point 1 ' at distillation system 2 tops, the original state of this position is temperature-50 ℃, pressure 0.3MPa.The establishment method of the explosion triangle of the coordinates regional of the coalbed methane containing oxygen in this separation process scheme and the position of the most easily blasting is referring to embodiment 1, wherein the starting point concentration of methane, oxygen and nitrogen is respectively 8%, 5% and 87%, and the original state of the tail gas outlet 1 ' of distillation system 2 is normal temperature and pressure.Y
0=8% upper explosive limit point Y less than explosion triangle
1=29.5%, be in the outer IV district of explosion triangle, in low-temperature liquefaction partitioning cycle process, can not blast, need not control the tail gas safe temperature out.
Embodiment 4
A kind of coalbed methane containing oxygen mixture, the at first cooling of the refrigeration system in the access to plant 1 of described coalbed methane containing oxygen, then enter distillation system 2 and be separated into tail gas and liquid pure methane, liquid pure methane flows out from the distillation system bottom, and tail gas flows out from the tail gas outlet 1 ' at the top of distillation system 2.
Because this separation system is without cold recovery, thus the position of the most easily blasting in the position of the tail gas exit point 1 ' at distillation system 2 tops, the original state of this position is temperature-50 ℃, pressure 0.3MPa.The establishment method of the coordinates regional of coalbed methane containing oxygen of position and the explosion triangle of the most easily blasting is referring to embodiment 1, wherein the starting point concentration of methane, oxygen and nitrogen is respectively 8%, 18% and 74%, and the original state of the tail gas outlet 1 ' at the top of distillation system 2 is normal temperature and pressure Y
0=8% upper explosive limit point Y less than explosion triangle
1=29.5%, be in the outer IV district of explosion triangle, in low-temperature liquefaction partitioning cycle process, can not blast, need not control the tail gas safe temperature out.
Claims (7)
1. method of separating purification methane from coalbed methane containing oxygen with low-temperature liquefaction, said method comprising the steps of: at first the unstripped gas of coalbed methane containing oxygen is lowered the temperature, then described coalbed methane containing oxygen is carried out rectification process, namely get the methane through separating-purifying, it is characterized in that
A) take the volumetric concentration Y of methane as X-coordinate, the volumetric concentration X of oxygen is ordinate zou, is used for setting up the coordinates regional for the coalbed methane containing oxygen of separation process scheme, and determines the explosion triangle of the position of the most easily blasting in this technical process;
B) the original volume concentration Y of the methane in the detection unstripped gas
0
C) work as Y
0Upper explosive limit point Y greater than explosion triangle
11.0～1.1 times the time, increase refrigerating duty, perhaps reduce raw gas flow, thereby reduce the temperature of this position;
D) repeating step is a) to c), until Y
0Be Y
11.0～1.1 times, the temperature of current this position is the safe separating minimum temperature, keeps above 0～5 ℃ of safe separating-purifying methane from coalbed methane containing oxygen of this temperature,
Wherein, the position of the most easily blasting in the described separation process scheme is the position of distillation system outlet, perhaps is the tail gas exit at distillation system top and the position between the cold recovery system outlet place,
Wherein, the explosion triangle of described coalbed methane containing oxygen is set up by the following method:
A) the volumetric concentration Y with methane is defined as the coordinate transverse axis, and the volumetric concentration X of oxygen is defined as the coordinate longitudinal axis, and the intersection point O (0,0) of two coordinate axis is true origin, and the volumetric concentration of methane is 100%, and the oxysome volume concentrations is that 0 point is defined as the B point;
B) straight-line equation of the mixed gas of methane and air in rectification process
With the intersection point of the coordinate longitudinal axis be A
1, tie point A
1, B forms the mixed gas straight-line equation A of methane and air
1B,
The volumetric concentration of expression oxygen, Y represents the volumetric concentration of methane;
C) Lower Explosive Limit point L, the upper explosive limit point V with the mixed gas of methane under the normal temperature and pressure and air is connected with critical explosion concentration point N, the explosion triangle LVN that forms coalbed methane containing oxygen under the normal temperature and pressure, LN is the Lower Explosive Limit line of coalbed methane containing oxygen under the normal temperature and pressure, and VN is the upper explosive limit line of coalbed methane containing oxygen under the normal temperature and pressure;
D) by under non-normal temperature and pressure, the Lower Explosive Limit point L of the mixed gas of methane and air under the temperature and pressure of the position of the most easily blasting in the technical process
1, upper explosive limit point V
1Make respectively the parallel lines of LN and VN, two parallel lines intersect at N
0Point, then trilateral L
1V
1N
0Be the explosion triangle of the coalbed methane containing oxygen under this temperature and pressure condition, L
1N
0Be the Lower Explosive Limit line of coalbed methane containing oxygen under this temperature and pressure condition, V
1N
0Upper explosive limit line for coalbed methane containing oxygen under this temperature and pressure condition;
E) the volumetric concentration Y of the methane in the coalbed methane containing oxygen of detection beginning rectification process
cVolumetric concentration X with oxygen
c, will put B(100,0) and some C(Y
c, X
c) connect, making the straight-line equation BC of coalbed methane containing oxygen, BC and the coordinate longitudinal axis intersect at A
0The point;
F) connect A
0Point, true origin O(0,0) and the B point obtain the coordinates regional A of the coalbed methane containing oxygen in the described separation process scheme
0OB;
G) BC and L
1N
0Or its extended line intersects at L
0, with V
1N
0Or its extended line intersects at V
0, tie point L
0, V
0And N
0, the explosion triangle L of the position that obtains the most easily blasting in the described technical process
0V
0N
0
2. method according to claim 1, it is characterized in that described methane is to separate by the following method to obtain from coalbed methane containing oxygen: the unstripped gas of coalbed methane containing oxygen at first enters the refrigeration system cooling, following described coalbed methane containing oxygen enters distillation system and carries out rectification process, flow out tail gas from the distillation system top, pure methane flows out from the distillation system bottom.
3. method according to claim 2 is characterized in that the described tail gas that flows out from the distillation system top enters described cold recovery system recoveries cold, flows out from the outlet of cold recovery system again.
4. method according to claim 3 is characterized in that described cold recovery system is throttling set or expansion gear.
5. according to claim 1 or 3 described methods, it is characterized in that described distillation system is rectifying tower.
6. according to claim 1 or 3 described methods, it is characterized in that described distillation system is comprised of gas-liquid separator and gas stripping column.
7. method according to claim 2 is characterized in that, described refrigeration system and described cold recovery system are in same device.
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| CN102206129B (en) * | 2011-04-02 | 2013-09-25 | 薛鲁 | Separation method for oxygen-containing coal bed gas |
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