Equiflow

UNIFORM DISTRIBUTION ENSURES A GREENER FUTURE

With motor fuel specifications becoming increasingly stringent, the industry-wide refinery objective is to push hydrotreating unit performance, including specification attainment and cycle length maximization. The vast majority of existing hydrotreaters operate with fixed-bed catalytic reactors in the “trickle-flow” regime. The ultra-low sulfur levels required by impending diesel fuel regulations make it essential to obtain effective catalyst utilization via optimum gas-liquid distribution.

EQUIFLOW: EXPERTISE, EXPERIENCE & INNOVATION IN HYDROTREATING

Over thirty years of middle distillate process innovation, catalyst manufacture, development, implementation and industrial feedback, has made Axens a world leader in hydrotreating. Our R&D efforts in this field are unequalled, going well beyond those of catalyst vendors and detailed engineering companies.

POWERFUL RESOURCES CONVERGED TO GET THESE RELIABLE RESULTS

A comprehensive program came up with significantly improved reactor internals, the EquiFlow distributor trays and mixing boxes. Refiners can now have an optimized utilization of all the catalyst in their reactors. Computational fluid dynamics (CFD) were applied to simulate flow properties of process fluids under operating conditions. Cold flow experimental mock-up units (top photo) were designed to validate the concept using hydrocarbon/gas mixtures.

a)

b)

Mock-up (a) and CFD images (b) inside a conventional design gas/liquid downcomer.

EquiFlow™ REACTOR INTERNALS FOR OPTIMAL CATALYST UTILIZATION

The first photo is an example of the fidelity of the CFD model results compared to mock-up flow results. Compared with flow conditions resulting from the use of conventional distributor trays (sieve tray & gas chimney, bubble cap, etc.) where the catalyst upper surface is only partially wetted, EquiFlow generates a highly uniform liquid phase throughout the reactor cross section. Gamma ray tomographic measurements were put into play with a high-precision gas/liquid collector system to demonstrate that this pattern remains steady throughout the height of the catalyst bed. With EquiFlow distributor trays, the entire catalyst volume is used, preventing hot spots from forming. The benefits to operations are: optimal utilization of the entire catalyst load; avoidance of pressure drop build-up due to coking of poorly irrigated catalyst veins; and avoidance of potential cracking zones.

Liquid distribution results obtained with a

conventional multi-downcomer distributor device and with EquiFlow. The dark blue color indicates flow deficiency; red shading - flow excess; intermediate

shades - near ideal gas/liquid ratios.

Ideal for retrofits, the distributors can be easily installed in existing, as well as new, reactors. EquiFlow distributors are not prone to plugging and have no higher pressure drop than conventional distributors. It is of major importance to minimize ΔP when more catalyst volume is added to meet future sulfur specifications.

HIGH EFFICIENCY MIXING BOX

For applications where highly exothermic reactions occur, it is advantageous to re-mix the effluents from previous reactor beds to ensure a uniform temperature profile before entering subsequent catalyst beds. High

efficiency mixing or quench boxes minimize the height requirements in the reactor and thus maximize the amount of catalyst that can be loaded into the same reactor volume. The thermal images that follow exemplify the increased mixing efficiency that is obtained with the EquiFlow mixing boxes. The EquiFlow system exhibits a significantly higher homogeneity in effluent temperature gradient compared to conventional designs found in many older units.

Mixing Box Inlet (viewed from above)

a) Conventional design b) EquiFlow design

Mixing Box Outlet (viewed from below)

a) Conventional design b) EquiFlow design The red and blue colors represent the temperatures of the inlet streams (example: temperature differential of the streams = 35°C). The turquoise, yellow and green colors in the EquiFlow mixing box outlet give proof of

the near-ideal average temperature of the mixed stream.

NEAR-PERFECT FLUID DISTRIBUTION: INDISPENSIBLE FOR ULSD

With the advent of ten ppm ultra-low sulfur diesel (ULSD) specifications, refiners will be looking at revamping their existing units, increasing operating severity and pushing their HDS units to the limit. That leaves no room for poor fluid distribution in reactors.

The best indicator of good fluid distribution in a catalyst bed, or the lack of it, is the degree of radial temperature spread in the reactor bed. Ideally it should be zero. Spreads of even a few degrees are now most undesirable, causing the following to happen: • The operator must raise severity or reduce throughput to the point at which his product meets the sulfur specification. • Utility consumption will usually increase, particularly hydrogen make-up. • Run cycles end prematurely, caused by inability to meet the sulfur specification and required plant throughput due to catalyst degradation or bed fouling.

PLANT RESULTS CONFIRM EQUIFLOW

As of June 2006, eighty-one units profit from EquiFlow technology in their design. The new internals are performing to expectations and have improved the unit operation. EquiFlow is now a standard feature of all new Axens’ hydrotreatment units. The results of a commercial ULSD revamping project are given in the above figure. In this particular case, only the second of two reactors was equipped with EquiFlow. The high and uneven per cent ratios of radial ΔTs to axial ΔTs observed in the first reactor beds indicate that fluid distribution could be improved.

By contrast, with EquiFlow internals in the second bed, radial ΔT spreads of less than a degree Celsius approach the ideal. This is also about the limit of commercial thermocouple precision.

GO AHEAD - IMPROVE YOUR MARGINS

EquiFlow internals ensure optimal catalyst utilization and enable on-spec production with longer cycle lengths.

GO FAR AHEAD: ACHIEVE MAXIMUM PROFITABILITY

If you want more paths to the summit of performance and profits, Axens offers them by way of catalysts and services. • HR series of premium hydrotreatment catalysts • APC, for optimized control of your unit using multi-variable controllers and inferential models. Short pay out times. • Catapac™, our high density catalyst loading technology that further ensures homogeneous flows and longer cycles – it is the best there is. • Axens’ technical assistance, continuing technical monitoring, evaluation and trouble-shooting services to follow your hydrotreater and ensure it performs to its intended goals.

A ve ra ge A xia l D elta T : 8 °C

0

40

80

1 2 0

0 6 0 1 20 18 0 2 4 0 3 0 0

T im e o n s tream , d a ys

R a dia l/A xia l D e lta T , %

A ve ra ge A xia l D elta T : 8 °C

0

40

80

1 2 0

0 6 0 1 20 18 0 2 4 0 3 0 0

T im e o n s tream , d a ys

R a dia l/A xia l D e lta T , %

A verage A xia l D e lta T : 8 °C

0

4 0

8 0

1 20

0 6 0 1 2 0 1 80 2 40 3 0 0T im e o n s trea m , d a ys

R a dia l/A xia l D elta T , %

A verage A xia l D e lta T : 8 °C

0

4 0

8 0

1 20

0 6 0 1 2 0 1 80 2 40 3 0 0T im e o n s trea m , d a ys

R a dia l/A xia l D elta T , %

A vera ge A xia l D e lta T : 7 °C

0

40

8 0

1 2 0

0 60 12 0 1 80 2 40 3 0 0T im e o n s trea m , d a ys

R ad ia l/A xia l D elta T , %

A vera ge A xia l D e lta T : 7 °C

0

40

8 0

1 2 0

0 60 12 0 1 80 2 40 3 0 0T im e o n s trea m , d a ys

R ad ia l/A xia l D elta T , %

R a dia l/A xia l D e lta T , %

A ve ra ge A xia l D elta T : 4 °C

0

4 0

8 0

12 0

0 60 1 20 18 0 24 0 3 0 0T im e o n s trea m , d a ys

A ve ra ge A xia l D elta T : 4 °C

0

4 0

8 0

12 0

0 60 1 20 18 0 24 0 3 0 0T im e o n s trea m , d a ys

H R S eries

H R S eries

E qu iF low

E qu iF low

D iese lF eed

N e w R e acto rw ith E qu iF lo w

E xis ting R eacto r w ithC onve n tion a l T ra ys

10 ppm S ulfur D iese l P roduct

H R S eries

H R S eries

R eg u la r T ra y

R eg u la r T ra y

Jun0

6-Eq

uiflo

w