Integrated Cheese Plant
--------------------------------------------------------------------------------------------------------This example deals with an integrated milk processing plant that produces cheese, butter, whey
protein concentrate (WPC), and food-grade ethanol. The development of the example was based
on data that are available in the literature (References 1 and 2).
The plant operates around the clock for 330 days a year and on a daily basis processes 2,000
metric tons of milk (83,333 kg/h) and produces 214 tons of cheese, 9 tons of butter, 211 tons of
WPC, and 28 tons of ethanol.
The plant consists of four sections: Cheese Making, Butter Making, WPC Making, and Ethanol
Making. The process step icons of the Cheese making section are displayed in black color; those
of Butter making in blue; WPC making in green; and Ethanol making in dark red. For information
on how to specify flowsheet sections and edit their properties, please see Chapter 7.1 of the
manual or consult the Help Facility (search for sections).
PROCESS DESCRIPTION
Cheese Production
Milk is pumped from tankers into any of six 227 m 3 (60,000 gal) silos (V-102), each mounted on
load cells to monitor the level of milk at any given time. The temperature in the silos is maintained
at around 4 oC. Milk from the silos flows through a pasteurizer (HX-101), which is a heat
exchanger operating at around 68 oC, and then to a cooler (HX-102) to reduce its temperature at
the inlet to the cheese vat to 30 oC. Lactic-acid starter culture and rennin are added in small
proportions to the contents of the vat (V-101). The cheese-making process results in the
solidifying curd, which is salted during the later stages of the process, and an aqueous whey
stream (S-107), comprising unconsumed proteins, fat, lactose and mineral salts. The cheese is
formed into blocks (R-102 and TB-101), sealed, cooled and stored to mature.
Butter Production
Using a centrifugal separator (DS-101), the whey stream (S-107, S-109) is separated into a fatrich cream (S-113) and a dilute aqueous stream (S-132) containing mainly proteins, salts, and
lactose. The cream is pasteurized as before (HX-103 and HX-104) and used as the feed for
making Grade B butter, which is sold for ingredient applications such as in bakery products.
Grade B is the highest possible grade for whey butter. The butter is packaged in cartons (FR102), which contain 30 kg of material. The butter whey stream (S-121) is combined with the dilute
aqueous stream (S-132) and is sent to the WPC section.
Whey Protein Concentrate (WPC) Production
The dilute aqueous streams (S-132 and S-121) from the Butter making section contain two further
potentially valuable components, albeit in low concentrations: whey proteins and lactose. The
whey proteins are concentrated, using crossflow ultrafiltration (UF-101), and then spray-dried
(SDR-101) to produce solid WPC containing 50-75 % protein. The dried WPC is stored in silos
(SL-101) and packaged in bags containing 22.5 kg (50 lbs) of material.
Ethanol Production
The liquid permeate from the ultrafilters (S-129) is treated further using reverse osmosis (RO101), which retains lactose and some of the mineral salts. The permeate of reverse osmosis (S119) goes through another reverse osmosis system (RO-102) to remove minerals. The result is
pure demineralized water, recycled as diafiltration water for ultrafiltration and as CIP sanitizing and
rinse water. Approximately 35 % of the water contained in the original milk is recycled. The
concentrated lactose solution is fed to any of eight batch fermentors (F-102), where a proprietary
strain of yeast is applied to produce ethanol in 24-hour fermentations. A centrifugal separator (DS-
102) recovers and recycles yeast from the “beer” after fermentation. Beer, 4 to 5 % alcohol at this
point, flows into any one of two beer wells (V-108), from which it is pre-heated through a plate
exchanger (HX-106) before distillation. The dilute ethanol solution is concentrated by distillation
(C-101) to spirit-grade levels. The distillation process step is a typical three-stage system
employing thermal vapor recompression to recover steam and using glycol as the azeotrope in the
first stage to boost alcohol from 180 to 200 proof.
MATERIAL BALANCES
The table below provides information on raw material requirements for the entire flowsheet. The
quantities are displayed in kg/year, kg/hour, and kg/MP Entity (MP Entity = Main Product Entity =
18 kg cheese block).
Raw Material
kg/Year
kg/Hour
kg/MP Entity
Milk
Starter
Renin
Salt
Yeast
660,000,000
6,600,000
660,000
1,412,811
3,009,600
83,333.3
833.3
83.3
178.4
380.0
168.11
1.68
0.17
0.36
0.77
Total
671,682,411
84,808.4
171.09
The above table was extracted from the Excel version of the Stream Report (see File \ Export
Reports to Excel...). The report was opened using Excel, edited, and pasted into this document.
The following table is from the Excel version of the Environmental Impact Report and provides
information on the amount of entering components that end up in waste streams. The proteins
and fat are not listed because they are fully utilized. The utilization of lactose is around 90%. In
terms of water, around 44% of the incoming water (contained in milk) ends up in waste streams.
The remaining is recovered as demineralized water (around 35% of the total) or remains in the
final products (as water content of cheese and butter). Overall, the plant is quite effective from an
environmental impact point of view.
Component
Name
Anions
Cations
Lactose
Water
Yeast
Plant Total
TOTAL
IN
(kg/h)
OUT AS
LIQUID WASTE
(kg/h)
333.3
250.0
4,083.3
72,666.7
380.0
308.1
231.1
381.2
32,139.2
723.1
100,402.5
34,298.8
COST ANALYSIS AND ECONOMIC EVALUATION
The essential results of cost analysis for the entire flowsheet are shown below.
Cost Item
$/Entity
$/Day
$/Year
%
Raw Materials
Equipment
Labor
Consumables
Lab/QC/QA
Waste Trtm/Disp
Utilities
36.15
5.72
1.89
0.63
0.09
0.24
2.24
430,114
68,101
22,473
7,451
1,124
2,881
26,610
141,937,515
22,473,334
7,416,000
2,458,912
370,800
950,763
8,781,366
76.98
12.19
4.02
1.33
0.20
0.52
4.76
Total
46.97
558,754
184,388,691
100.00
Raw materials contribute 77% of the total operating cost, followed by equipment-dependent cost
(12.2%), utilities (4.8%), and labor (4%). The unit cost of milk was assumed $0.2/kg ($0.8/gal).
Further, it was assumed that the plant employs 100 operators that are evenly distributed among
the 4 sections. The unit cost of cheese is $47/block or $2.61/kg ($1.18/lb).
The table below provides information on the contribution of each flowsheet section to total
operating cost. As can be seen, the Cheese making section contributes around 79% of the total
cost, followed by Ethanol making (13.6%), and WPC making (5.8%).
Cost Item
Cheese
$/year
Butter
$/year
WPC
$/year
EtOH
$/year
Subtotal
$/year
%
Raw Materials
Equipment
Labor
Consumables
Lab/QC/QA
Waste Trt/Dsp
Utilities
140,782,641
2,344,016
1,854,000
92,700
1,274,487
266,936
1,854,000
92,700
13,526
101,514
5,679,984
1,854,000
1,735,703
92,700
1,292,340
1,053,360
14,182,398
1,854,000
723,210
92,700
950,763
6,201,013
141,937,515
22,473,334
7,416,000
2,458,912
370,800
950,763
8,781,366
76.98
12.19
4.02
1.33
0.20
0.52
4.76
Subtotal
146,347,844
2,227,162
10,756,241
25,057,444
184,388,691
100.00
Contribution (%)
79.37
1.21
5.83
13.59
100.00
The above two tables were extracted from the Excel version of the Itemized Cost Report (ICR) of
this example.
Information on Capital Investment and Project Economic Evaluation follows below:
Equipment Purchase Cost ($)
Direct Fixed Capital ($)
Working Capital ($)
Total Capital Investment ($)
18,417,000
119,782,000
14,462,000
140,233,000
Annual Operating Cost ($)
184,389,000
Revenues ($/year)
Cheese
WPC
Ethanol
Butter
Total Revenues
176,671,000
6,201,000
15,052,000
7,901,000
205,825,000
Return on Investment (%)
Payback Time (years)
IRR (after taxes) (%)
17.3
5.78
11.2
The above results, along with additional information, can be found in the Economic Evaluation
Report (EER) of this example. They are also displayed on the Executive Summary dialog (View \
Executive Summary).
To calculate the revenues, the following prices were assumed for the product and by-products of
the plant: cheese is sold for $2.5/kg ($45/block or $1.13/lb), butter is sold for $2.67/kg ($1.21/lb),
WPC is sold for $0.88/kg ($0.403/lb) and ethanol is sold for $1.63/kg ($0.74/lb).
REFERENCES
[1] C.A. Zaror and D.L. Pyle, “Process design: an exercise and simulation examples”, in
Chemical Engineering for the Food Industry, Edited by P.J. Fryer, D.L. Pyle and C.D. Rielly,
Published in 1997 by Blackie A & P, an imprint of Chapman & Hall, London, ISBN 0 412 49500
7.
[2] Charles E. Morris, “Golden Cheese Company of California”, Chilton’s Food Engineering,
March, 1986.