World Grain - December 2016 - 51

FEED OPERATIONS

Natural gas stock loss (%)
Flue gas
O2 content
percentage

Flue gas temperature - combustion air temperature (degrees F)
230

250

270

290

310

330

350

370

390

410

430

450

470

490

510

1

14.49

14.92

15.36

15.79

16.23

16.67

17.11

17.55

17.99

18.43

18.88

19.32

19.77

20.21

20.66

2

14.72

15.17

15.63

16.09

16.55

17.01

17.47

17.93

18.39

18.86

19.32

19.79

20.26

20.73

21.20

3

14.98

15.46

15.95

16.42

16.90

17.38

17.87

18.36

18.84

19.33

19.82

20.31

20.80

21.30

21.79

4

15.26

15.77

16.28

16.79

17.29

17.81

18.32

18.83

19.35

19.86

20.38

20.90

21.41

21.93

22.46

5

15.59

16.12

16.66

17.20

17.74

18.28

18.82

19.36

19.91

20.46

21.00

21.55

22.10

22.65

23.20

6

15.96

16.52

17.10

17.67

18.24

18.82

19.39

19.97

20.55

21.13

21.71

22.29

22.88

23.46

24.05

7

16.38

16.98

17.59

18.20

18.82

19.43

20.04

20.66

21.28

21.90

22.52

23.14

23.77

24.39

25.02

8

16.86

17.51

18.16

18.82

19.48

20.14

20.80

21.46

22.12

22.79

23.46

24.12

24.79

25.47

26.14

9

17.42

18.13

18.83

19.54

20.25

20.96

21.68

22.39

23.11

23.83

24.55

25.27

25.99

26.72

27.44

10

18.09

18.86

19.62

20.39

21.16

21.94

22.71

23.49

24.27

25.05

25.83

26.62

27.41

28.19

28.98

11

18.89

19.73

20.57

21.42

22.26

23.11

23.96

24.81

25.67

26.52

27.38

28.24

29.10

29.97

30.83

12

19.87

20.80

21.73

22.66

23.60

24.54

25.48

26.43

27.37

28.32

29.27

30.22

31.18

32.13

33.09

Source: Fred Fairchild

needed to deliver steam to the system.
Avoid short cycling times when the
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back again. To avoid these problems,
the boiler should be equipped with
PRGXODWLQJ FRQWUROV WR DGMXVW WKH ¿Uing rate based on demand.
A term that is used in steam is "steam
quality." This term is used to describe
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the steam. A 100% steam quality
means that the source is all steam and
no water. A 90% quality steam would
have 90% steam and 10% water.
This term becomes important when
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where it is used and whether that qualLW\ PDNHV D GLIIHUHQFH7KH LQFOXVLRQ
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the steam lines or heat loss through
under insulated piping.

installed on the continuous blowdown
stream to preheat the water going to
the boiler while cooling the blowdown.
2. An economizer (heat exchangHU PD\ EH LQVWDOOHG RQ WKH ÀXH JDV
H[KDXVW RI WKH ERLOHU WR SUHKHDW WKH
PDNHXSZDWHUZKLOHUHGXFLQJWKHÀXH
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275 degrees F.
3. Maintain condensate traps in good
working order. A leaking trap may allow steam to blow through directly
into the condensate return system. This
steam is then lost to the system and requires that additional steam be made
to replace that lost through the leaking
trap. A leaking trap with a ¼-inch diameter opening in a 100 psig system will
leak 163 pounds per hour. In a year's
WLPH RI FRQVWDQW OHDN RQ D V\VWHP RSerating 24 hours per day, 1,427,880
KEYS TO HIGH EFFICIENCY
SRXQGVRIVWHDPPD\EHORVWIURPWKLV
Following are some points to keep VLQJOHGHIHFWLYHWUDS
in mind to operate the steam system
4. Keep all steam piping properly inDQGJHWWKHKLJKHVWHI¿FLHQF\DQGFRQ- sulated to make sure steam reaches its
trol costs.
destination in the best quality. Assume
1. The continuous blowdown water \RX KDYH D IRRW VHFWLRQ RI LQFK
IURP WKH ERLOHU LV KRW DQG FDQQRW EH VWHDP SLSH ZLWK D V\VWHP SUHVVXUH RI
sent to a regular sewer system unless 100 psig. The line temperature is 300
it is cooled. A heat exchanger may be degrees F and the boiler operates 6,000
www.World-Grain.com / World Grain / December 2016

KRXUV SHU \HDU ,I WKH SLSH LV XQLQVXlated, the bare pipe will lose 508mm
%78VSHU\HDUEXWZLWKLQFKRIJRRG
insulation, that loss would be reduced
to 46mm BTUs per year. Thicker insuODWLRQZLOOIXUWKHUUHGXFHWKHORVV
7R VXPPDUL]H WKH VHOHFWLRQ RI D
properly equipped boiler with the adGLWLRQRIDZDWHUVRIWHQLQJV\VWHPDQG
proper chemical treatment is a must.
Pre-heat the boiler makeup water using an economizer on the exhaust
stack. Installing a heat exchanger on
the continuous blowdown also may
help preheat the boiler makeup water. Establish a monitoring program
to make sure all traps and other accessories are operating properly. Properly
insulate and maintain steam supply
lines. A properly designed and operated steam system will keep energy
costs as low as possible.
Fred Fairchild is feed science professor emeritus
in the Department of Grain Science at Kansas
State University. Prior to coming to Kansas State
in 1994, he worked in the industry designing,
constructing and commissioning numerous mill
facilities. He is a licensed professional engineer.
He may be reached by e-mail at fjf@k-state.edu.
We want to hear from you - Send comments and
inquiries to worldgrain@sosland.com. For reprints of
WG articles, e-mail reprints@sosland.com.

51
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