(214b) The Technical Reconstruction of the Double Effect Distillation for Methanol Process

The Technical
Reconstruction of the Double Effect Distillation for Methanol Process

Chengtian Cui¹,
Changning Guo¹, Botao
Xie², Xujie Zhang³, Weiwei Bai², Jinsheng
Sun¹

¹ School of Chemical Engineering and Technology, Tianjin
University, No.92 Wei Jin Road, Tianjin 30072, China

²Baofeng Group, Ningdong Town, Wuling 750411, China

³Department of Chemical
Engineering, East China University of Science and Technology, No.130 Mei Long
Road, Shanghai 200237, China

Methanol is
one of important basis raw materials of chemical industry and also an excellent
environment-friendly fuel, which make it as a significant commodity in the
global market. Distillation is an essential unit operation for purified
production of methanol. Product quality, production cost, environmental impact
and energy consumption are largely related to distillation process.

Our research
effort, under this circumstance, has been devoted since 2002 to energetically
optimize 4-column methanol distillation system that is widely adopted in
methanol units from coal, with reduced cycling water requirement. This patented
process technology saw its industrial application in Chinese largest single
unit of 1800Kt/a of Baofeng Group
located at North China, with the lowest steam consumption of 0.9/1 t(steam)/t(methanol) compared with normally 25% higher for
both simulative case study and on-site operation. Methanol product is in
accordance with O-M-232G and the recycling water is reduced significantly from
67 t(CW)/t(methanol) to 52 t(CW)/t(methanol).

The flow
diagram of this advanced double effect distillation process is showed in Fig.1.
Its advantages arise for limitations found in current units: (1) heat exchange
network failed to fully recover energy causing large CW flow to remove extra
heat; (2)for pressured column, bubble point reflux
need larger reflux ratio than the sub-cooled; (3) the heat of distillate from
pressured column was normally ignored; 
(4) the low concentration of methanol of feed inlet to recovery column
leads to higher reflux radio, responsible for unsatisfied unit energy
efficiency.

Fig.1 The
double effect distillation process.

(Column1.Light
ends column; Column 2.Pressured column;

Column 3.Atmospheric
column; Column4.Recovery column)

As a
solution, a new flow diagram is built up and showed in Fig.2. (1) HEN totally
reorganized (not completely show); (2) sub-cooled reflux to pressured column
caused 10% reduction to the reflux ratio, economizing steam consumption; (3)
top product of pressured column give heat to crude methanol before feeding
light ends column; (4) change product and by-product position of recovery
column to give efficient unit energy consumption.

Fig.2 The
reconstruction of distillation process.

(Column1.Light
ends column; Column 2.Pressured column;

Column
3.Atmospheric column; Column4.Recovery column)

It is
estimated that the production of methanol will be over 60 million tons in 2014.
If this reconstruction could be applied in the whole methanol industry, 1.3
million tons of standard coal would have been saved. This is equivalent to
reduce 5 million tons emission of carbon dioxide, so the environmental impact
can be largely decreased. Field operation shows reconstruction perfect
substitution worth to spread to the whole methanol industry, energetically
efficient and low environmentally impacting.