NEW MACHINERY AND EQUIPMENT

INCREASING THE EFFICIENCY OF AEROBIC FERMENTATION UDC 663.15.033

V. L. Borisov and A. M. Kuznetsov

At present, the production technology of edible protein suffers from two major drawbacks: contamination of the environment and high specific power consumption (SPC). The fermentation systems used in the main production stage (biosynthesis of microorganisms) can be described by the well-known indexes of oxygen dissolution rate (ODR) [i] and SPC in its dissolution [2]. The ODR and thus the output of the fermentation system can be increased by some methods. For example, the ODR can be increased by increasing the aerating gas flow. In equipment with agitators, however, the ODR is associated with the SPC in mixing. At some values of specific power, increasing the aerating gas flow does not enlarge the contact surface of the phases because of coalescence. The excess gas, without dispersing, passes through the fermentation system as large bubbles. Thus, there is an optimum aerating gas flow for each level of the SPC in mixing. Increasing the SPC reduces the bubble diameter and raises the gas content and the volume mass transfer coefficient. It should be pointed out that the bubble diameter is minimal at SPC 5-8 kW/m s and raising it further is futile. One of the most promising methods of intensifying the production of edible yeasts is to increase the prooess motive force by increasing the oxygen partial pressure in the aerating gas. This can be effected by increasing the total pressure in the system or using industrial oxygen. Most fermenters now working in the microbiological industry are designed to work at atmospheric pressure and hence pressure can be raised no more. Most promising is the use of "oxygen aeration" or the use of technical and technological methods that permit the use of industrial oxygen or its mixture with air in certain proportions for aerating the culture medium. A high ODR can thus be achieved with better technoeconomic indexes and improved ecology. Published information and the authors' studies showed that the fermenter output can be increased while simultaneously eliminating the discharge of the spent gas into the atmosphere by organizing a closed circuit gas exchange in the fermentation system. As a result of the fuller oxygen utilization, the SPC decreases and the installation and operation of the air-fractionating plant are amortized. Plant tests were carried out in an experimental unit of capacity V r = 0.32 m 3 with closed circuit gas flow using oxygen-enriched air for aeration. These tests aimed at experimental verification of the possibilities and evaluation of the technoeconomic process parameters of culturing microorganisms on petroleum n-paraffins. The test unit layout is shown in Fig. i. The spent gas from the fermenter is fed by a compressor to an absorber for CO 2 purification. The latter is absorbed by water and the cleaned gas again fed to the fermenter through a receiver (additional equipment like a condenser and dephlegmator are possible). The oxygen plant meets the oxygen requirements and its flow is controlled by a ratio regulator. Table 1 shows the process parameters and the test results. Plant test results show that the fermenter output x increases directly proportionally to the increase of the volume proportion of oxygen in the aerating gas (Fig. 2); The volume proportion of dissolved oxygen was 2-5% of saturation under the given aerating conditions. The results of microbiological control showed that, on aerating with oxygen-enriched air, the cells of microorganisms were uniform and rounded; a reduction of vacuolized cells was noticed; and pseudomicelial forms and extraneous microflora decreased by 2-4 times. This suggested that the activity conditions of microorganisms did not change but, on the other hand, oxygen concentration in the culture improved. The closed circuit gas flow demonstrated its efficiency and ensured practically full utilization of technical oxygen as a result of its repeated circulation without any discharge into the atmosphere. Based on these results, an industrial unit was designed with closed circuit gas flow and aeration with oxygen-enriched air for a 50 m 3 capacity fermenter and oxygen plant K-0.4 to obtain the basic data for modernizing the working plants producing paprin. Translated from Khimicheskoe

i Neftyanoe Mashinostroenie,

0009-2355/90/0102-0003512.50

No. i, pp. 4-5, January,

9 1990 Plenum Publishing Corporation

1990. 3

TABLE 1 ~,~

x

S~

s

~,

yCO~

21 31 40

17,9 26 35,5

1,4 21 27

1,6' 1,3 2,6

'2,9' 5,1 6,7

z 0,3 1,4 1,9

MO=

MCO'

uS

.4,93

3,i4 4,23 5,3

I",16 1,18 1,22

8,44 1,22

o, 2,2 ' 2,36 2,44

2,24 3,57 4,59

O~

EO=

0,26 0,3 0,31

1,22 0,71 0,51

*T:heoreticai value (for single passage of gas).

Note.

i) Gas equilibrium constant mDc = 3.4 m 3.

MPa/kg 0=.

2) Symbols:

Yi and yf) Initial and final

volume proportion of the component of gas mixture, %; x) weight concentration of microorganisms, kg/m3; S o and S) initial and final concentration of substrate, kg/m3; MO 2) ODE, kg 02/(m3"h); MCO 2) CO 2 desorption rate, kg C02/(m3"h); ~S and ~02) consumption coefficients with respect to substrate and oxygen, kg/kg absolute dry matter; x) fermenter output, kg/(mS'h); and E02) SPC in oxygen dissolution~ kW/kg 02`

i Fig. i. Layout of the test plant with closed circuit gas flow; i) oxygen plant; 2) receiver; 3) drive; 4) fermenter; 5) absorption tower; and 6) gas flow booster. 9 kg/(#.h)

i:

I

I

L I.I /,/[/

4

2

fO~

0,1

42

,,

0,4

y),%

F i g . 2. Dependence of output x of the f e r m e n t e r on the volume proport i o n of oxygen yOz in the a e r a t i n g gas: i) V r = 0.12 m s , specific power N v = 5.5 kW/m 3, gas flow u = 6.9 m3/h; 2) V r = 0.12 m 3, N v = 6 kW/m 3, Vg = 11.2 m3/h; and 3) V r = 0.i m 3, N v = 9.2 kW/ma; u =

12.2 mS/h.

LITERATURE CITED io

2.

N. N. Vasil'ev, V. A. Ambrosov, and A. A. Skladnev, Modeling the Processes of Microbiological Synthesis [in Russian], Lesn. Prom., Moscow (1975). U. ~. Viestur, A. M. Kuznetsov, and V. V. Savenkov, Fermentation Systems [in Russian], Zitnane, Riga (1986).

EFFECT OF TRIBOTECHNICAL PROPERTIES OF THE THREADED SURFACES OF PUMPING-REPRESSURING PIPES ON THEIR CAPACITY TO BE SCREWED TOGETHER WITH MECHANICAL WRENCHES UDC 622.245.001.5

V. !. Kuts

Threaded connections of pumping-repressuring pipes (PRP) pertain to joints in which external friction forces prevent relative movement of the parts. Here, the type of deformation in the zones of actual contact of the connected parts has a significant effect on the interaction of friction contact. It is of interest to analyze the processes occurring in screwing together the PRP from the point of view of friction. The author has obtained a formula for determining the nominal radial pressures in the separation boundary of the connected parts based on the general (moment) theory of deformation of shells. In this, Lame's formulas were applied for calculating contact pressures on surfaces sufficiently remote from the edge sections. The formula obtained has the form 0~ =

2A tg q~E6p6s

(1)

where Pr is the nominal radial pressure; A is the nominal axial tension; ~ is the angle of inclination of the mean thread diameter line to the pipe axis; E is the modulus of elasticity of the pipe material; 6p and 6s are the calculated wall thickness of the pipe and sleeve, respectively, at the section with coordinate X = 0; K(x) and $(x) are dimensionless parameters [I];

q-(l+~)(l § 6 s + 6 s2/4 R,s) 2 ]; R s, Rp is the radius of the median surface in the section with the coordinate X = 0; ~ is the Poisson's ratio; indices "s" and "p" refer to parameters of the sleeve and pipe, respectively. It is pointed out in [2] that, to a significant extent, displacements of pipe connections assembled with axial tension occur due to deformation of the microroughnesses. Formulas for determining the variation in the height of roughnesses in relation to axial tension are given in [3-5]. However, calculations using these dependences do not account for the strength groups of the materials, as a result of which, results obtained differ significantly from one another. Thus, axial wear-in tension A w is 1.3439569 mm [3], 1.91993 mm [4], and 3.175 mm [5]. As indicated in [6], more accurate values of A w can be obtained by using the method in [7] for determining the yielding capacity of thread turns which possess roughness and waviness at the contact surfaces. The design diagram of a threaded connection is given in Fig. i. Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. i, pp. 5-7, January, 1990. 0009-2355/90/0102-0005512.50

9 1990 Plenum Publishing Corporation

5