Issue 23/2013 - Innovative Technologies Maximize olefin production revenue

Innovative technologies to maximize olefin production revenues

□ MICHAEL J.
TALLMAN, VICE PRESIDENT OF PETROCHEMICAL TECHNOLOGY, KBR'S TECHNOLOGY DIVISION

The price of raw materials is a decisive factor
in the cost of ethylene production.
The feedstock used for steam cracking comes from natural gas or crude oil
.
Western European and Asian ethylene plants are mainly naphtha-based, while the Middle East, North America and Southeast Asia are mainly natural gas
.
The development of shale gas in North America has led to an increase
in the price differential between natural gas and crude oil.
In anticipation of large quantities of low-cost ethane feedstock, more than a dozen producers in North America have announced plans to build new ethylene plants, and ethylene production in North America is expected to increase
significantly in the coming years.
When most ethylene producers in North America are also investing in retrofitting their existing crackers to increase capacity and adapt to lightweight feedstocks, it is important
to choose a pyrolysis technology with high ethylene selectivity.
For a plant of comparable size, lightweight feedstock and high ethylene yield mean less feedstock is used, resulting in fewer cracking by-products and less
impact on the existing plant's olefin recovery process.

1.
Advantages of KBR cracking furnace

KBR's cracking furnace adopts "single tube stroke" furnace tubes, and the residence time is generally 0.
1~0.
15 seconds, which is shorter and can achieve higher ethylene yield, as shown
in Figure 1.

At present, the ability of ethane crackers to operate at high conversion rates is another important factor
in improving yields.
The unconverted ethane needs to be processed in the recovery section and returned to the cracking furnace, which occupies the space between the recovery section and the
cracking furnace.
KBR's cracking furnaces can operate continuously with
an ethane conversion rate of more than 75%.
Combined with high ethylene selectivity and high ethane conversion rate, ethylene production capacity can be increased by up to 10%.


The pyrolysis furnace layout structure is also a key factor
in the renovation or expansion of the pyrolysis furnace.
KBR's design uses a single, compact, cabin-type radiation chamber
.
The pyrolysis capacity of the radiation chamber is large, and the capacity of a single naphtha cracking furnace can be as high as 200,000 tons/year, while the capacity of a single ethane cracking furnace is more than 200,000 tons/year
.
The design occupies less space than other similarly sized crackers that commonly use a dual-radiation chamber structure – an important consideration
in retrofit projects.

As a result, KBR's unique cracker design and structure offer significant advantages
for retrofitting or expansion of existing ethylene plants.

2.
Impact faced by liquid cracking furnace

At present, liquid cracking furnaces are more common in Europe and Northeast Asia, and their ethylene production costs are the highest in the
world.
These ethylene plants, which are mainly liquid raw materials, have become "marginal producers" and will be under the dual pressure
of market benefits and production costs.

The key issue in the olefin industry is the availability and price of by-products, such as propylene and butadiene
.
Globally, the total production of such by-products from steam crackers will gradually decrease, as a direct result
of the use of ethane and other natural gas associated light hydrocarbons as feedstocks.
Ethane is an excellent raw material for ethylene production, using modern cracking furnaces and adopting full cycle operation, the final yield of ethylene is more than
80%.
However, compared to other pyrolysis feedstocks, propylene and butadiene yields are extremely low, at about 2%
each.
Propylene and butadiene have traditionally come mainly from steam cracking
of liquid feedstocks such as naphtha or gas oil.
Lightweighting has caused a shortage of supply of propylene and butadiene, resulting in a sharp rise and fall in the price of butadiene, which is volatile
.
It is predicted that the price of propylene and butadiene will remain above its historical average
in the future.

The key strategy for liquid crackers to remain competitive is to maximize the production of high value-added by-products such as propylene, butadiene and aromatics
.
Most liquid cracking furnaces can achieve this strategy
by reducing the cracking depth and increasing the propylene/ethylene production ratio (P/E).

These challenges have prompted many manufacturers to look for alternative ways
to produce propylene and butadiene.
Propane dehydrogenation plants have been investigated by several companies, and while such units are capital-intensive, they are reasonable as long as there is sufficient profit between low-cost propane feedstock and high-value propylene products
.
Many countries in China and the rest of Asia are producing butadiene exclusively through oxidative dehydrogenation – also an extremely capital-intensive project
.

3.
Characteristics of KBR catalytic cracking technology

KBR uses catalytic cracking technology to produce olefins, which can be integrated with traditional steam cracking technology to create synergies
.
These catalytic technologies focus on propylene and aromatics, and the specific design can be tailored
to the type of feedstock.
KBR's catalytic olefin technology uses fluidized bed catalytic cracking (FCC) in a process facility similar
to that of FCC units in conventional refineries.
KBR's catalytic olefin technology incorporates a unique, innovative, patented design to address the fact that
feedstock is much lighter than FCC feedstock in conventional refineries.
The regional flow of KBR catalytic cracking to olefin reactor is shown in Figure 2
.

Like all refinery FCC units, this reactor (converter) consists of four parts: riser/reactor, where all cracking reactions take place; Settler, which separates the pyrolysis gas from the catalyst; Stripper to recover the exhaust gas entrained by the catalyst; Regenerator, which uses air for combustion to remove coke
formed on the surface of the catalyst.
The accessory system of the FCC unit includes an air supply unit, a flue gas treatment and heat recovery unit, and a catalyst storage device
.

The propylene yield of fresh naphtha is close to twice that of steam cracking, and the typical P/E is close to 1.
0 (compared with 0.
5~0.
6 for traditional steam cracking).

Catalytic cracking of olefin-rich feedstocks, such as C4/C5 by-products of olefin plants, can have propylene yields of up to 40% and P/E of about 2.
0
.

This technology is particularly beneficial
for producers currently using naphtha cracking to produce olefins.
The results show that by adding a catalytic olefin production device and integrating with the naphtha cracking olefin plant, the circulating catalytic cracking of C4 extractant, a section of hydrogenation C5 and gasoline non-aromatic hydrocarbon extraction can increase the operating profit of the existing steam cracking plant with an annual output of 1 million tons by 55 million ~ 65 million US dollars / year
.
Catalytic olefins also have some flexibility in terms of feedstock, and mixed C4 products can be pre-processed as required, such as extraction of butadiene, isobutylene or 1-butene (PE comonomer), before returning to the catalytic olefin converter
.

The integration of catalytic olefin production with conventional steam cracking technology can greatly improve the yield and P/E of olefins (ethylene + propylene), which is suitable for
both new construction and expansion/retrofit projects.

4.
Flexible technology is the key to future competitiveness

Flexibility in plant operation is the focus of new plant or renovation projects, which can flexibly respond to changes in market dynamics and continuously adjust business strategies in specific periods to maximize
profits.

At the same time, the cracking of fresh naphtha raw materials in pyrolysis furnaces and catalytic olefin converters allows manufacturers to face changing market conditions and make timely adjustments
to the product structure.
While traditional pyrolysis processes provide higher butadiene yields and slightly higher ethylene yields from most feedstocks, catalytic olefin converters provide higher propylene and aromatic
yields.
By flexibly transferring fresh raw materials (or recycled materials) to crackers or FCC-type reactors, producers can continuously change production to maximize product yield
.

Catalytic olefin plants offer significant flexibility for feedstocks, as they are suitable for other materials besides fresh naphtha and C4 and C5 by-products of steam cracking: olefin-rich feedstocks from refinery FCC, coking or viscosity cracking units, which cannot be used for conventional steam cracking unless hydrotreated; Oxygen-based materials, such as methanol, ethanol or other oxygen-based substances, can be converted to olefins
in FCC reactors.

Many olefin producers are looking for ways to improve operating margins, as well as alternative technologies for "specialized" propylene production, which are bound to become more prevalent
in the future.
KBR's olefin technology is economical and, when combined, offers the flexibility to respond to unpredictable market conditions
.