DD295655A5 - METHOD FOR THE OPTIMAL CONTROL OF THE FILTRATION PROCESS IN DEEP-REFINING PLANTS - Google Patents

Abstract

The invention relates to a process for the optimal control of the filtration process in dewaxing plants. It is applicable to the dewaxing of mineral oils with the help of selective solvents. The process according to the invention is essentially characterized in that a dimensionless expression is calculated from the time-cyclically measured amount of filtrate and the mean value of the filtrate quantity calculated in the process calculator after each measurement and this is compared with the number of measurements and, depending on the result of the comparison, the measurement cycle is continued or the signal for termination the filtration phase and the beginning of the warm washing phase is given. Thus, a maximum filtrate throughput in cycle time is achieved, regardless of product type and filter medium type. {Dewaxing plant; Control; filtrate; Average; Cycle time; Meszzyklus; Meszwertanzahl; Filtration phase; Hot washing phase; Prozeszrechner}

Description

where t _{w is} the duration of the warm wash phase, t _{M is} the measurement cycle time, V _{1 is} the ith measurement of the amount of filtrate, and V _{m is} the average of the filtrate amount for the first through i th measurements, then the value of A is the run index i compared, in the comparison result i less than A, the measuring cycle continues and in the comparison result i equal to greater than A aborted the measuring cycle and the process computer is given the signal to cancel the filtration phase and the beginning of the warm washing phase.

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Field of application of the invention

The invention relates to a process for the optimal control of the filtration process in dewaxing plants, which is particularly applicable in the dewaxing of mineral oils using selective solvents for the production of lubricating oils.

Characteristic of the known state of the art

It is known in the dewaxing of mineral oils to cool the paraffin-containing feed oil with the addition of solvents in the crystallization stage, resulting in paraffin precipitation from the oil, and to use filter apparatuses for solid-liquid separation. The resulting in the dewaxing solvent-oil-paraffin suspension is separated in the filtration stage in the products filtrate, consisting of solvent and oil, and slack wax, consisting of the paraffin crystals with oil and solvent fractions; as described for example in DD-PS 234437. The filtration stage usually consists of vacuum drum cell filters connected in parallel, with one to four-stage filter systems being used, depending on the dewaxing process.

It is also known to operate these filters cyclically. The actual filtration phase with a temporally decreasing filtrate throughput follows the warm washing phase, in which the filter medium is regenerated. The steadily decreasing filtrate throughput as a function of time results from the temporal change of the filter medium resistance. As a result of the clogging of the pores of the filter medium by the finest paraffin crystals, the filter medium resistance increases steadily during the filtration phase, so that the filtrate throughput finally decreases sharply. At a certain reduced filter performance, the filter is then washed with warm solvent, which dissolves the wax crystals and makes the filter medium permeable again. Filtration time and wash time together give the cycle time. The optimum filtration process with respect to a maximum filtrate throughput in the cycle time results from the correct choice of the beginning of the warm washing phase.

From the literature it is known that the temporal change of the filter medium resistance and thus the filtrate throughput is not exactly, but only empirically represented. Thus, the determination of the optimal start of the warm-washing phase is mathematically exactly impossible.

According to SCHPANOV and GUTIN, the average filtrate quantity for the filtration phase is 0.7 to 0.8 times the amount of filtrate with a clean filter medium.

BRL) K and GAINZEVA have attempted to find an optimality criterion by means of an exponential approach for changing the filter medium resistance. Disadvantage of this method is that the constants needed in the approach can only be determined by a variety of experiments and for each feed other values for the constants must be used. Furthermore, with such an approach certain influential factors in the filtration in dewaxing systems are not detected, for example, the time-varying resistivity of the compressible filter cake, so that a calculation does not lead to the goal.

In DE-PS 3116610 a method for controlling a filter system is proposed, according to which the number of filter cycles is controlled until regeneration or replacement of the filter means by an effective criterion to be calculated in each cycle. Disadvantage of this method is the complicated determination of the proposed effectiveness criterion.

Object of the invention

The aim of the invention is the development of a simple method for optimal control of the filtration process in dewaxing with little technical effort, which causes a high throughput of the filtration plant.

Presentation of the essence of the invention

The invention has for its object to control the filtration process in dewaxing the optimal cycle time and thus to determine the beginning of the warm washing phase regardless of the feedstock and the Filtermittelart. According to the invention, the process for optimally controlling the filtration process in dewaxing units by determining the amount of filtrate, comparison of the amount of filtrate with a predetermined function variable in a process computer coupled to the plant, termination of the filtration phase as a function of the comparison result after a certain time and the start of the warm washing phase characterized essentially characterized in that the amount of filtrate is measured at equal intervals and stored in the process computer, the average value of the filtrate in the process computer is calculated and stored after each measurement, and starting from the second measurement after each measuring cycle in the process computer the value of the dimensionless expression

V _m -Vi

where t », the duration of the warm washing phase, t _M the measuring cycle time, Vi the i-th measured value of the filtrate quantity and V _m the mean value of the filtrate quantity for the first to i-th measurement, then the value of A with the index of rotation i compared, in the comparison result i less than A of the measurement cycle continues and in the comparison result i equal to or greater than A aborted the measurement cycle and the process computer is given the signal to cancel the filtration phase and the beginning of the warm wash phase. Due to the filtrate throughputs which practically occur during the dewaxing of mineral oils and taking into account the available storage capacities and computing speeds of modern process computers, values between 10 and 500 seconds are expediently selected as the measurement cycle time.

The optimum duration of the filtration phase results in the value of i * t _M , which can additionally be printed out by the process computer.

Surprisingly, it has been found that only the cyclic measurement of the amount of filtrate and the comparison of the absolute value with the mean in the form of a dimensionless expression provides an optimality criterion, which guarantees the optimal control of the filtration process with respect to a maximum filter performance.

In contrast to the known methods of filter control no data of the product or the filter are required, so that the inventive method is applicable regardless of product type and type of filter medium.

The cycle time of the filter results from the sum of the filtration time i * t _M and the laundry time _w . With the process computer signal to terminate the filtration phase and the beginning of the warm wash phase is guaranteed that the enforced in the cycle time Gesamtfiltratmenge is maximum. Any shorter or longer filtration time than that determined according to the invention results in a lower total filtrate throughput.

The process according to the invention has the following advantages over the known processes for controlling the filtration process in dewaxing plants:

- Optimum control of the filtration process in dewaxing units, regardless of product type and type of filter medium,

- low technical complexity and simple execution of the method,

- Securing a maximum filtrate throughput and thus a high filter performance.

embodiment

The invention will be explained in more detail below using an exemplary embodiment.

To prepare a lubricating oil component, a paraffinic mineral oil is deparaffinized in a dewaxing plant with the solvent mixture butanone toluene. The resulting in the crystallization stage suspension is separated by parallel vacuum drum cell filter in the products filtrate and slack wax.

Due to the entering filter medium dislocation by fine paraffin crystals, the amount of filtrate decreases during the filtration phase, so that after a certain filtration time of the filter is switched to the warm washing phase. The filter is washed with hot solvent, whereby the filter medium becomes permeable again. Thereafter, the filtration phase begins again.

According to the invention, the filtration process is controlled by the cyclic measurement of the filtrate amount of a vacuum drum cell filter. The measured absolute value V | is stored in a process computer coupled to the dewaxing plant. After each measuring cycle, the mean value V _{m of} the filtrate quantity in the process computer is calculated and stored.

The measuring cycle time of the filtrate tM is 5 min. The duration of the warm washing phase of the filter tw is 30 min. The time course of the filtrate quantity V of a vacuum drum cell filter with a filter area of 50 m ² and a polyacrylonitrile fabric as filter medium is shown in FIG.

Starting with the second measured value V ₂ , after each measuring cycle in the process computer, the value of the dimensionless expression

A = 6 · ^^

calculated and compared with the running index i.

Table 1 shows, in extracts, the measured values V 1 stored in the process computer, the calculating mean value V _m and the calculated value of A, in each case as a function of the running index i.

Table 1: Process Calculation Values

Vi in m ³ / h V _n , in mVh

1 18 18 - 2 17.9 17.95 2148 3 17.8 17.9 1068

10 17.4 17.6 522

20 16.8 17.4 168

30 16.4 17.141

50 15.4 16.6 77

60 15,1 16,3 76

65 15.0 16.2 75 66 14.9 16.2 69 67 14.9 16.2 69 68 14.8 16.2 63 (i> A)

In the range 2 <i <67, i is smaller than A, so that the measurement cycle is continued. For i = 68, i is greater than A, so that

aborted the measuring cycle and the process computer, the signal to cancel the filtration phase and the beginning of the

Warm washing phase is given. The optimal duration of the filtration phase is the value of the process computer

i · tM = 68 · 5 = 340min.

Taking into account t _w , the optimum cycle time of the filter is then i · t _M + t _w = 370 min.

Claims (1)

Process for optimal control of the filtration process in dewaxing by determining the amount of filtrate, comparison of the amount of filtrate with a given function variable in a process computer coupled to the plant, termination of the filtration phase as a function of the comparison result after a certain time and the beginning of the warm washing phase, characterized in that the filtrate Measured at equal intervals and stored in the process computer, calculated and stored after each measurement, the mean of the filtrate in the process computer, starting from the second measurement after each measurement cycle in the process computer, the value of the dimensionless expression л - tw Vi t _M V _1n -V-,