阅读说明：本技术 一种快速确定天然气液化工艺冷剂适宜配比的方法 (Method for rapidly determining appropriate ratio of natural gas liquefaction process refrigerant ) 是由 范峥 姬盼盼 孔劼 李文君 田润芝 景根辉 刘钊 于 2019-09-27 设计创作，主要内容包括：本发明提供一种快速确定天然气液化工艺冷剂适宜配比的方法,通过对冷剂中n种组分x<Sub>i</Sub>进行编码,将自然变量x<Sub>i</Sub>变成规范变量z<Sub>i</Sub>,再根据实验方案利用流程模拟软件得到不同参数条件下的冷剂单位冷量<Image he="44" wi="78" file="DDA0002219068230000011.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>建立起冷剂单位冷量<Image he="42" wi="63" file="DDA0002219068230000012.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>与规范变量z<Sub>i</Sub>之间的高阶回归方程,通过规划求解的方法得到该高阶回归方程的各项回归系数,进一步计算得到适宜冷剂单位冷量<Image he="47" wi="151" file="DDA0002219068230000013.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>条件下各规范变量z<Sub>i</Sub>的取值,从而可以得到与适宜冷剂单位冷量相对应的冷剂中各组分的百分比,即得到天然气液化工艺冷剂适宜配比。装置现场验证结果表明,按照本发明方法优化冷剂配比后,天然气液化工艺的实际单位能耗大大降低。(The invention provides a method for quickly determining the proper ratio of a natural gas liquefaction process refrigerant, which is implemented by adding n components x in the refrigerant i Encoding the natural variable x i Becomes the norm variable z i And then the unit cold capacity of the refrigerant under different parameters is obtained by utilizing the process simulation software according to the experimental scheme Establishing unit cold quantity of starting refrigerant And a specification variable z i The high-order regression equation is obtained by a planning and solving method, and the proper unit cold capacity of the refrigerant is obtained by further calculation Each normative variable z under the condition i Is taken from the value of (a) thusThe percentage of each component in the refrigerant corresponding to the unit cold quantity of the proper refrigerant can be obtained, and the proper proportion of the natural gas liquefaction process refrigerant can be obtained. The on-site verification result of the device shows that the actual unit energy consumption of the natural gas liquefaction process is greatly reduced after the refrigerant proportion is optimized according to the method disclosed by the invention.)

1. A method for rapidly determining the appropriate ratio of natural gas liquefaction process refrigerants is characterized by comprising the following steps:

first, with x₁、x₂、…、x_n-1And x_nThe percentage of each of n components in the refrigerant is expressed, the percentage of each component is non-negative, and the sum of the percentages of the components is 1; x is the number of_iSubject to the constraints that are imposed by,

x_i≥a_i，i＝1,2,...,n-1,n

second step, for x_iEncoding the natural variable x_iBecomes the norm variable z_iSo that x is_iIs converted into z of more than or equal to 0_i1 or less, wherein i is 1,2, n-1, n; then

Thirdly, determining a corresponding basic data combination scheme according to the component number n in the refrigerant, and obtaining different standard variables z through process simulation software_iRefrigerating agent unit cold capacity under combined condition

Fourthly, simulating the unit cold capacity of the obtained refrigerant according to the basic data combination scheme

fifthly, the unit cold quantity of the refrigerant in the fourth step high-order regression equation

sixthly, cooling proper refrigerant in unit

2. The method for rapidly determining the proper ratio of natural gas liquefaction process refrigerants according to claim 1Method characterized by a_iX is 0_i＝z_i，i＝1,2,...,n-1,n。

3. The method for rapidly determining the proper ratio of natural gas liquefaction process refrigerants according to claim 1, wherein in the third step, the basic data combination scheme is shown in the following table:

4. the method for rapidly determining the proper ratio of natural gas liquefaction process refrigerants according to claim 1, wherein in the fourth step,

wherein the content of the first and second substances,

5. the method for rapidly determining the proper ratio of the natural gas liquefaction process refrigerants according to claim 1, wherein in the fifth step, the high-order regression equation is calculated by a planning and solving method to obtain each normative variable z under the condition of the unit refrigeration capacity of the proper refrigerants_iThe value of (a).

6. The method for rapidly determining the proper ratio of the refrigerants in the natural gas liquefaction process according to claim 1, wherein in the fifth step, the unit cold energy of the proper refrigerants is calculated according to the theoretical unit energy consumption of the refrigeration liquefaction process and by combining the actual natural gas processing capacity, the actual energy utilization efficiency, the actual cold insulation rate and the actual refrigerant circulation quantity of a refrigeration device.

7. The method for rapidly determining the proper ratio of the refrigerants in the natural gas liquefaction process according to claim 6, wherein the calculation formula of the unit cold capacity of the proper refrigerants is as follows:

in the formula (I), the compound is shown in the specification,is suitable for the unit cold quantity of the refrigerant, kJ/kg refrigerant;

8. The method for rapidly determining the proper ratio of refrigerants in a natural gas liquefaction process according to claim 1, wherein in the sixth step, the unit cold of the proper refrigerants is used

x₁＝[1-(a₁+a₂+...+a_n-1+a_n)]z₁+a₁

x₂＝[1-(a₁+a₂+...+a_n-1+a_n)]z₂+a₂

...

x_n-1＝[1-(a₁+a₂+...+a_n-1+a_n)]z_n-1+a_n-1

x_n＝[1-(a₁+a₂+...+a_n-1+a_n)]z_n+a_n。

9. the method of claim 1, wherein in the third step, the process simulation software is ASPEN Plus, ASPEN HYSYS or CHEMICAL CAD.

Technical Field

The invention belongs to the field of natural gas liquefaction, and particularly relates to a method for quickly determining a proper ratio of refrigerants in a natural gas liquefaction process.

Background

With the increasing problem of environmental pollution, natural gas is used as a novel high-quality clean fuel and is applied more and more widely in the fields of energy, traffic, chemical industry and the like. At present, there are two main ways for natural gas transportation: one is pipeline transportation, although the gas transportation amount is large, the transportation cost is high, and a pressurizing station and an adjusting station are additionally arranged along the pipeline; the other is liquefaction transportation, namely purified natural gas is frozen to be liquid at minus 162 ℃ under one atmospheric pressure by adopting a refrigeration process, and the liquefied natural gas is 1/600 when the volume is only gaseous, so that the problem of inconvenient transportation of the gas can be effectively solved, and favorable conditions are provided for realizing transnational trade and recycling of small, scattered and small natural gas resources.

The method for liquefying natural gas at home and abroad is more, and mainly comprises a cascade refrigeration liquefaction process, a multi-stage single-component refrigeration liquefaction process, a mixed refrigerant refrigeration liquefaction process with precooling, an expander refrigeration liquefaction process and the like. If the cold energy provided by the refrigerant is less than the cold energy required by the liquefaction of the natural gas from the cold energy balance perspective of the natural gas liquefaction device, the natural gas liquefaction rate is insufficient, and the product yield is reduced; when the cold energy provided by the refrigerant is larger than the cold energy required by the liquefaction of the natural gas, the cold energy carried by the refrigerant is redundant, and the energy consumption of the device is increased. Therefore, the proper natural gas liquefaction process refrigerant proportion not only can obviously reduce the energy consumption of the device and improve the product yield, but also can greatly reduce the production cost and improve the enterprise competitiveness.

However, since the on-site operator often cannot accurately and reliably adjust the refrigerant ratio to timely cope with the change of the production condition in the actual operation process of the device, the cold absorbed by the lng and the cold provided by the refrigerant are difficult to be perfectly matched, so that the processing capacity of the device is often low or the energy consumption of the system is increased.

Disclosure of Invention

The invention aims to provide a method for quickly determining the appropriate ratio of a refrigerant in a natural gas liquefaction process, and solves the problem that the cold energy absorbed by liquefied natural gas and the cold energy provided by the refrigerant in the prior art are difficult to form ideal matching.

The invention is realized by the following technical scheme:

a method for rapidly determining the appropriate ratio of natural gas liquefaction process refrigerants comprises the following steps:

first, with x₁、x₂、…、x_n-1And x_nThe percentage of each of n components in the refrigerant is expressed, the percentage of each component is non-negative, and the sum of the percentages of the components is 1; x is the number of_iSubject to the constraints that are imposed by,

x_i≥a_i，i＝1,2,...,n-1,n

second step, for x_iEncoding the natural variable x_iBecomes the norm variable z_iSo that x is_iIs converted into z of more than or equal to 0_i1 or less, wherein i is 1,2, n-1, n; then

Thirdly, determining a corresponding basic data combination scheme according to the component number n in the refrigerant, and obtaining different standard variables z through process simulation software_iRefrigerating agent unit cold capacity under combined condition

Fourthly, simulating the unit cold capacity of the obtained refrigerant according to the basic data combination schemeEstablishing unit cold quantity of refrigerant

And a specification variable z_iThe high-order regression equation is solved to obtain each item regression coefficient of the high-order regression equation;

fifthly, the unit cold quantity of the refrigerant in the fourth step high-order regression equationReplaced by proper refrigerant unit cold energy required by natural gas liquefaction

And substituting each regression coefficient into the regression coefficients to calculate each standard variable z under the condition of proper unit cold quantity of the refrigerant_iTaking the value of (A);

sixthly, cooling proper refrigerant in unit

Each normative variable z under the condition_iConversion to natural variable x_iTo obtain proper refrigerant ratio.

Preferably, a_iX is 0_i＝z_i，i＝1,2,...,n-1,n。

Preferably, in the third step, the basic data combination scheme is as shown in the following table:

preferably, in the fourth step,

wherein the content of the first and second substances,

preferably, in the fifth step, the high-order regression equation is calculated by a planning and solving method to obtain each normative variable z suitable for the unit refrigeration capacity condition of the refrigerant_iThe value of (a).

Preferably, in the fifth step, the unit cooling capacity of the suitable refrigerant is calculated according to the theoretical unit energy consumption of the refrigeration liquefaction process and by combining the actual natural gas processing capacity, the actual energy utilization efficiency, the actual cold insulation rate and the actual refrigerant circulation capacity of the refrigeration device.

Further, the calculation formula of the unit refrigeration capacity of the suitable refrigerant is as follows:

in the formula (I), the compound is shown in the specification,

is suitable for the unit cold quantity of the refrigerant, kJ/kg refrigerant;

the energy consumption per unit of theory of different refrigeration and liquefaction processes is kJ/m³Natural gas; q_LNGFor practical natural gas processing capacity, m³Natural gas/h; eta is the actual energy utilization efficiency; ζ is the actual cold insulation rate; q_RKg refrigerant/h as the actual refrigerant circulation amount.

Preferably, in the sixth step, the appropriate refrigerant is used for cooling

Each normative variable z under the condition_iConversion to natural variable x_iThe concrete formula is as follows:

x₁＝[1-(a₁+a₂+...+a_n-1+a_n)]z₁+a₁

x₂＝[1-(a₁+a₂+...+a_n-1+a_n)]z₂+a₂

...

x_n-1＝[1-(a₁+a₂+...+a_n-1+a_n)]z_n-1+a_n-1

x_n＝[1-(a₁+a₂+...+a_n-1+a_n)]z_n+a_n。

preferably, in the third step, the process simulation software is ASPEN Plus, ASPEN HYSYS or CHEMICAL CAD.

Compared with the prior art, the invention has the following beneficial technical effects:

the invention is prepared by adding n components x in the refrigerant_iEncoding the natural variable x_iBecomes the norm variable z_iAnd then the unit cold capacity of the refrigerant under different parameters is obtained by utilizing the process simulation software according to the experimental scheme

Establishing unit cold quantity of starting refrigerant

And a specification variable z_iThe high-order regression equation is obtained by a planning and solving method, and the proper unit cold capacity of the refrigerant is obtained by further calculation

Each normative variable z under the condition_iThe percentage of each component in the refrigerant corresponding to the unit cold quantity of the proper refrigerant can be obtained, and the proper proportion of the natural gas liquefaction process refrigerant can be obtained. The on-site verification result of the device shows that after the refrigerant proportion is optimized according to the method, the actual unit energy consumption of the natural gas liquefaction process is greatly reduced and is not greatly different from the theoretical unit energy consumption obtained by calculation, meanwhile, the energy utilization rate of the device is maximized, and the energy-saving effect is very obvious.

Detailed Description

The present invention will now be described in further detail with reference to specific examples, which are intended to be illustrative, but not limiting, of the invention.

The invention discloses a method for quickly determining the appropriate ratio of a natural gas liquefaction process refrigerant, which comprises the following specific steps:

firstly, according to theoretical unit energy consumption (see table 1 in detail) of different refrigeration and liquefaction processes, the unit refrigeration capacity of the appropriate refrigerant is calculated by combining the actual natural gas processing capacity, the actual energy utilization efficiency, the actual cold insulation rate and the actual refrigerant circulation volume of each device.

TABLE 1 theoretical specific energy consumption for different refrigeration liquefaction processes

Refrigeration liquefaction process	Theoretical specific energy consumption (kJ/m)3Natural gas)
		Cascade refrigeration liquefaction process	1152
Single-stage mixed refrigerant refrigerating and liquefying process	1440
		Propane precooling single-stage mixed refrigerant refrigerating and liquefying process	1325
Multi-stage mixed refrigerant refrigerating and liquefying process	1210
		Single-stage expansion refrigeration liquefaction process	2304
Propane precooling single-stage expansion refrigeration liquefaction process	1958
		Two-stage expansion refrigeration liquefaction process	1958

In the formula (I), the compound is shown in the specification,the refrigeration capacity of the appropriate refrigerant unit required by the natural gas liquefaction is kJ/kg refrigerant;

the energy consumption per unit of theory of different refrigeration and liquefaction processes is kJ/m³Natural gas; q_LNGFor practical natural gas processing capacity, m³Natural gas/h; eta is the actual energy utilization efficiency; ζ is the actual cold insulation rate; q_RKg refrigerant/h as the actual refrigerant circulation amount.

And secondly, setting constraint conditions of refrigerant ratio. With x₁、x₂、…、x_n-1And x_nIndicating the percentage of each of the n components in the refrigerant, it is required that the proportions of each component must be non-negative and that their sum must be 1, i.e. 1

Meanwhile, in addition to the above constraints, if x_iSubject to other constraints, exist

x_i≥a_i，i＝1,2,...,n-1,n

a_iIs a respective variable x_iCorresponding minimum value (lower limit).

Third step, for x_i(i 1, 2.,. n-1, n) and encoding a natural variable x_iBecome the ruleNorm variable z_iSo that x is_iIs converted into z of more than or equal to 0_iIs less than or equal to 1, at the moment

Namely, it is

For the natural gas liquefaction process refrigerant consisting of n components, the percentage of each component is x₁、x₂、…、x_n-1、x_nIs constrained by the following constraint x₁≥a₁、x₂≥a₂、...、x_n-1≥a_n-1、x_n≥a_nIt can be known that

a₁+a₂+...+a_n-1+a_n＜x₁+x₂+...+x_n-1+x_n＝1

Therefore, the temperature of the molten metal is controlled,

x₁＝[1-(a₁+a₂+...+a_n-1+a_n)]z₁+a₁

x₂＝[1-(a₁+a₂+...+a_n-1+a_n)]z₂+a₂

...

x_n-1＝[1-(a₁+a₂+...+a_n-1+a_n)]z_n-1+a_n-1

x_n＝[1-(a₁+a₂+...+a_n-1+a_n)]z_n+a_n

it is to be noted that if each component x_iIs 0, then x_i＝z_iAt this time, the natural variable x_iAnd a specification variable z_iAre equal in value.

Fourthly, determining a corresponding basic data combination scheme according to the component number n in the refrigerant, and obtaining the unit refrigeration capacity of the refrigerant under different parameter conditions through a process simulation experiment, which is detailed in table 2. The flow simulation software is ASPEN Plus, ASPENHYSYS or CHEMICAL CAD.

TABLE 2 refrigerating fluid unit capacity under different parameter conditions

Fifthly, simulating to obtain the unit cold capacity of the refrigerant according to the basic data combination scheme

Establishing unit cold quantity of refrigerantAnd a specification variable z_iAnd further solving each item regression coefficient of the high-order regression equation.

Wherein the content of the first and second substances,

y_ji、y_jand y_iIs used as a test index.

Sixthly, cooling capacity per unit of refrigerant

And a specification variable z_iThe unit refrigeration capacity of the proper refrigerant can be predicted by a planning and solving method through a high-order regression equation between the two and related constraint conditions

Each normative variable z under the condition_iThe value of (a).

Seventhly, cooling proper refrigerant in unit

Each normative variable z under the condition_iConversion to natural variable x_iThus, an appropriate refrigerant ratio can be obtained.