Chemical Engineering July 2017 - 15

absorption is more efficient at higher
pressure, explains Paz Munoz, a process
engineer at Stamicarbon. Deciding
between the two processes
is a tradeoff between capital expenditures
(capex), and operating costs
(opex), which are related to the costs
of feedstock, utilities and energy,
says Stamicarbon's van Denderen.
thyssenkrupp Industrial Solutions
Nitric acid
~80% consumption
Fertilizer
~15% consumption
Non-fertilizer
AN
Dual-pressure processes
The general trend today is for bigger
plants, and companies are looking
closely at the total cost of ownership,
says van Denderen. " That means efficiency
[of the NA plant] is very important. "
Dual-pressure technology
is especially competitive for production
capacities of 500-600 metric
tons per day (m.t./d) and upwards,
he says. With this in mind, Stamicarbon
has revitalized its dual-pressure
technology, he says.
Munoz will introduce Stamicarbon's
newest dual-pressure process
at the Ammonium Nitrate - Nitric
Acid Producers Group (AN-NA)
conference (October 1-6; Austin,
Tex.), with a presentation entitled
" An improved dual-pressure nitric
acid process with maximum energy
recovery. " The company declined to
reveal any details in advance, but van
Denderen says that " the energy efficiency
of our design is unbeatable. "
Last year, Weatherly Inc., a wholly
owned subsidiary of KBR Inc. (Houston;
www.kbr.com) also introduced
a new dual-pressure technology for
producing NA at a large scale.
KBR Weatherly's dual-pressure
process (for more details, see Chem.
Eng., October 2016, p. 8) is said to
deliver lower operating costs with its
more efficient heat-recovery design.
Tailgas exits the system at 620°C,
compared to the lower (490°C) temperature
of alternative processes.
This enables more efficient recovery
of heat that is subsequently used to
generate energy to power up the system.
As a result, the new process offers
an operating cost advantage over
competing technologies of $4-5/ton
of NA produced, says the company.
" Over the past 20 years, about a
quarter to a third of the plants [built
by thyssenkrupp] have been mono
pressure, but the trend is toward
dual pressure plants, " says thyssenNP
AN
(technical grade)
Chemicals
CN
CAN
UAN
Uses of nitric acid:
AN: ammonium nitrate
NP: nitrophosphate
CN: calcium nitrate
CAN: calcium ammonium nitrate
UAN: urea ammonium nitrate solution
ASN: ammonium sulphate nitrate
TDI: toluene diisocyanate
MDI: methylene diphenyl diisocyanate
ASN
Caprolactam
Adipic
acid
Dinitrotoluene
TDI
Polyamide
6
Polyamide
6.6
Polyurethane
(Flexible
PU)
Nitrobenzene
MDI
Polyurethane
(Rigid
PU)
FIGURE 2. Nitric acid is used for a number of applications, with the bulk going into the production of
fertilizers
krupp's Groves. " For small plants
(up to around 500 m.t./d) we would
still consider mono-pressure design, "
he says.
The present style of dual-pressure
plant with a sieve-trayed absorber
was introduced in the 1970s, Groves
says. " Of course, there have been
many improvements, " he adds.
Ammonia oxidation catalysts
The NH3 oxidation catalyst is typically
a gauze composed of platinum group
metals (PGMs). Over the decades,
the gauze has been refined and optimized.
For example, Hereaus GmbH
(Hanau,
Germany; www.heraeus.
com) first began supplying Pt-wire
gauzes for NH3 oxidation
in 1916, and subsequently
replaced the Pt
wire with platinum-rhodium
wire gauzes in 1928.
Today, the company now
supplies gauzes with diameters
greater than 6
m. In the 1990s, Hereaus
introduced its FTC
(functional total
Air
Ammonia
Tailgas
control)
gauzes designed to reduce
the formation of
N2O emissions by 50%.
(N2O is a combustion byproduct
that is a greenhouse
gas (GHG) with a
global-warming potential
(GWP) that is 265 times
higher than CO2.) More
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
JULY 2017
Process
water
recently, Heraeus also introduced a
secondary catalyst that reduces N2O
emissions by up to 95%.
Johnson Matthey plc (JM; London,
U.K.; www.matthey.com) also
offers a variety of Pt-based gauzes
with unique production and knitting
patterns. For example, its Eco-Cat
technology uses palladium in a controlled
manner to replace some of the
Pt in the gauze. Exploiting its metalrecovery
properties, the Pd catches
lost Pt without compromising the
NH3 conversion. This increases the
gauze performance and gives a sustainable
and efficient system for NA
production, says the company.
In 2014, the Platinum Engineered
Compression
Air
Combustion
NO gas
Energy recovery
NO gas
Gas cooling
NO gas
+ acid condensate
Absorption
Tailgas
Tailgas treatment
Block diagram of nitric acid process
thyssenkrupp Industrial Solutions
FIGURE 3. Industrial production of nitric acid uses the Ostwald
process, which involves ammonia oxidation, followed by absorption
of NO2
15
Nitric acid
Tailgas
Excess energy
NO gas

http://www.matthey.com http://www.kbr.com http://www.heraeus http://WWW.CHEMENGONLINE.COM

Chemical Engineering July 2017

Table of Contents for the Digital Edition of Chemical Engineering July 2017