REPORT

ON

STUDY OF REFORMER FURNACE

AND IT’S OPTIMIZATION

By

Mr. YASHPAL TOMAR

SARDAR VALLABHBHAI

NATIONAL INSTITUTE OF TECHNOLOGY

SURAT (GUJARAT)

Guided by:

Mr. LOLUR RAGHVENDRA PRASAD

Area manager (NHT/CCR/HMU)

Essar oil ltd.

Jamnagar (Gujarat)

ACKNOWLEDGEMENT

To say that industrial training at Essar oil, Vadinar was a wonderful experience and would be an understatement. It has been nothing short of an experience that was intellectually fulfilling, mentally satisfying and professionally enriching. So it is inevitable that I should differentially acknowledge all those individuals who have made it so.

My project guide, Mr. Lolur Raghvendra Prasad, has been generous with his advice and counsel whenever I have approached him in any dilemma. I am grateful to his taking out time for me despite his tight schedule to prod me in right direction.

I must acknowledge the considerable contributions from Mr. Rajnesh Yadav Mr. Shashikant Rajan who helped me academically as well as by motivating throughout my training period.

In the end I would like to thank Miss Pelsida D’souza for providing me with this golden opportunity to gain practical knowledge of what I have studied in college.

Thankyou

Company profile:

About ESSAR OIL ltd.

The Essar Oil Ltd grass roots refinery in Gujarat, India (started in 1996) was completed and commissioned in 2006 (commissioned in third quarter). The refinery project was delayed several times due to environmental concerns and financial problems, including initial cost over runs and a shortfall in equity contributions.

Now the refinery is complete it is expected to produce between 10.5 and 12 million tonnes of processed products a year (mmtpa). The refinery employs over 1,000 personnel (the construction process required between 3,000 and 4,000).

The refinery is now the second largest in India after the Reliance Jamnagar refinery on an adjacent site which can produce over 27mmtpa.

Future plans

The refinery will be able to produce 5.5mmtpa of diesel and 2.2mmtpa of gasoline. Essar Oil is still following an aggressive plan to open over 2,500 retail outlets for their fuels and oil products across India.

Essar mission

“ To create enduring value for customers and stakeholders in core manufacturing and service business , through world-class operating standards state of the art technology and the positive attitude of our people.

Introduction:

There are various units for the production of petroleum products

The various units are :

1. CDU – CRUDE DISTILLATION UNIT

2. VDU – VACUUM DISTILLATION UNIT

3. FCCU – FLID CRACKING UNIT

4. VBU – VISBREAKER UNIT

5. NHT – NAPHTHA HYDROTREATER UNIT

6. CCR – CONTINUOUS CATALYTIC REFORMER

7. DHDS – DIESEL HYDRO DESULFURISATION

8. SRU – SULFUR RECOVERY UNIT

9. PIT – PROCESS INTERMEDIATE TANK

10. COT – CRUDE OIL TANK

Refinery typical block diagram:

Configuration:

Crude mixes:

The following crude mixers where consider for the configuration studies to ensure sufficient flexibility in the refinery operation:

1. 70% wt Arabian light / 30% wt Arabian heavy

2. 50% wt Arabian light / 50% wt Arabian

3. 100% wt Bombay high

4. 50 % wt Gulfaks / 50 % wt Oseberg

The refinery configuration is given below

1. CDU producing off-gas, overhead naphtha, heavy naphtha, light naphtha, light and heavy kerosene, light and heavy gas oil for diesel product blending and atmospheric residue.

This is department under which I had undergone my training.

2. VDU processing the atmospheric residue from CDU, producing vaccum distillate for diesel product + blending, Light Vacuum Gas Oil ( LVGO ), Heavy Vacuum Gas Oil (HVGO) , Heavy Heavy Vacuum Gas Oil and Vacuum Residue.

3. VBU, which thermally cracks thee vacuum residue. The VDU produces heavy gasoline, gas oil and atmospheric residue. Atmospheric residue is sent to the vacuum flasher producing visbreaker vacuum gas oil and vacuum flashed residue. Flashed vacuum residue, depending on the feed stock, is used to produce power plant feed, plant fuel oil and MV2 Fuel Oil.

4. HCU processing HVGO and a part of the LVGO from VDU and the gas oil from VBU. The HCU produces LPG, light naphtha for direct gasoline blending, heavy naphtha, high quality middle distillates for kerosene and diesel blending and a bottoms product.

5. FCC processing the bulk of the HHVGO and LVGO from VDU, HCU bottoms product and part of the bottom product residue from VDU. The FCC unit produces LPG, gasoline, light cycle oil for diesel product blending and fuel oil blending.

6. NHT, processing CDU overhead naphtha, VBU gasoline, HCU heavy naphtha and part of the FCC gasoline. The NHT product is split into light naphtha and heavy naphtha.

7. CCR, processing hydrotreated heavy naphtha from NHT. The CCR produces high octane reformate for gasoline blending.

8. HMU, processing light naptha and / or saturated LPG producing high purity hydrogen for HCU.

9. KMU to treat heavy naphtha, light and heavy kerosene from CDU for aviation turbine fuel, kerosene and diesel product.

10. The following is the summary of the core process unit capacities :

POWER GENERATION:

THERE ARE MAINLY TWO SOURCES OF POWER:

1. From Gujarat board : 25 MW , 220 KV

2. From its own power plant : 78 MW , 11 KV

CONTINUOUS CATALYTIC REFORMING:

OBJECTIVE OF THE CCR UNIT:

“Octanizing” is IFP’s registered reforming process using Continuous Catalyst regeneration.The purpose of the Octanizing process is to produce high octane number reformate for production of gasoline and hydrogen rich gas.Octanizing feed is generally straight run naphtha mixed with cracked naphtha.

BASIS OF DESIGN:

The Reformer unit design capacity = 900 000 MTPA

On stream time per year = 8000 hr. /year

A turn down ratio = 50%

UNIT MMTPA

CDU 10.50

VDU 5.05

NHT 1.36

CRU 0.90

HCU 2.20

FCCU 1.69

VBU 1.64

HMU 0.03

The design of the Regeneration loop = 57 kg/hr of coke burnt

In normal operation, expected coke formation = 32 kg/hr

(Catalyst flow rate is around 820 kg/hr)

FEED & PRODUCT SPECIFICATION:Hydro treated Heavy Naphtha (from Splitter bottom):

The four major catalytic reforming reactions are :-

1: The dehydrogenation of naphthenes to convert them into aromatics as exemplified in the conversion methylcyclohexane (a naphthene) to toluene (an aromatic), as shown below:

2: The isomerization of normal paraffins to isoparaffins as exemplified in the conversion of normal octane to 2,5-Dimethylhexane (an isoparaffin), as shown below:

3: The dehydrogenation and aromatization of paraffins to aromatics (commonly called dehydrocyclization) as exemplified in the conversion of normal heptane to toluene, as shown below:

4: The hydrocracking of paraffins into smaller molecules as exemplified by the cracking of normal heptane into isopentane and ethane, as shown below:

CCR FLOW DIAGRAM :

Process of continuous catalytic reforming:

1. Heavy naphtha coming from the NHT is only applicable to reforming light naphtha is not because the molecules will not participate in the above reactions.

2. Heavy naphtha coming at 120 C is sent to PACKINOK EXCHANGER where hydrogen and heavy naphtha mixed are passed through a number of plates exchanging heat through product of reforming alternatively.

3. Temperature of hydrogen + HN rises to about 410 C passed to feed heater ( 30F001) where it is heated to about 520 C and then to reactor.

4. Reactor (30R001) is moving bed catalytic reactor in which catalyst is falling from top under the effect of gravity and come in contact with the preheated feed.

5. then the temperature falls to approx. 360 C. again it is passed to second heater and the temperature is increased to about 520 C and then to reactor. Four heater and four reactor works simultaneously in the same manner.

6. Now the catalyst’s activity reduces during the reactions hence catalyst is continuously sent to regenerator. In the figure above it is shown.

7. after the reactor the hydrogen is produced in large amount, the product hydrogen+reformate+C1+C2+C3+C4+HCl+LPG is passed to packinok exchanger where the heat transfer was going on.

8. Then the product at 100 C is passed to finfan air cooler ( 30EA-001) cooled to about 60 C and then send to cooling water cooler ( 30 E-002 A/B).

9. Then the cooled product is sent to separator where hydrogen and the reformate separated and then the hydrogen from the top is send to centrifugal compressor (30 K-001). Pressure is increased from 2.5 Kg/cm2 to 5.5 Kg/cm2. One stream is sent to feed to maintain hydrogen HN ratio and another is sent to a series of reciprocating compressors ( 30 K002A/B/S) pressure is increased to about 25 Kg/cm2.

10. Reformate is pressurized through centrifugal pump and mixed with pressurized hydrogen. Then the liquid part is separated from hydrogen.

11. Hydrogen is sent to chloride adsorber ( 30R – 005 A/B ) from HCl is separated and the hydrogen is sent to DHDS, NHT.

CCR FURNACE

UNIT CAPACITY – 0.9 MMTPA

CCR

FURNACE

30F001*

Feed

30F002

Feed

30F003

Feed

30F004

Feed

30F005

Stabilizer

Reboiler

HEAT

DUTY

13.12

Gcal/hr

12.96

Gcal/hr

9.66

Gcal/hr

8.42

Gcal/hr

5.96

Gcal/hr

Inlet

Temp.

400 452 440 435 236

Outlet

Temp.

520 520 520 520 247

Number of 8 8 8 8 4

burner

Feed

Rate

183

m3/hr

183

m3/hr

183

m3/hr

183

m3/hr

--

Burner

type

Single

FG

Double

FG+FO

Double

FG+FO

Single

FG

Single

FG

In 30F001, 30 resembles the unit number and F resembles the furnace and 001 resembles that it is first heater.

Since the heat of ccr furnace is very HIGH that’s why optimization of furnace is required so even a small increase in efficiency can save a lot of money.

Fired furnace:An industrial furnace or direct fired heater, is an equipment used to provide heat for a process or can serve as reactor which provides heats of reaction.

General diagram of fired heater:

Radiant section :

The radiant section is where the tubes receive almost all its heat by radiation from the flame.

Convection section:

The convection section is located above the radiant section where it is cooled to recover additional heat.

Burner :

The burner in the vertical, cylindrical furnace as above, is located in the floor and fires upward.

They introduce fuel and air in the correct proportions, mix the fuel gas and air, provide a source of ignition, and stabilize the flame. Good combustion requires three steps:

1. Fuel and air in correct quantities

2. Thorough mixing of fuel and air

3. Sustained ignition of the mixture

Stack:

1. The flue gas stack is a cylindrical structure at the top of all the heat transfer chambers.

2. The stack damper contained within works like a butterfly valve and regulates draft (pressure difference between air intake and air exit) in the furnace, which is what pulls the flue gas through the convection section.

3. The stack damper also regulates the heat lost through the stack.

STACK

Types of furnace:

Based on draft:

Comparison between flue gas pressure inside the furnace and outside pressure.

Natural Draft

This is the most common type of draft with the air drawn into the furnace by means of the draft created

by the stack. The taller the stack, the greater the draft available.

Forced Draft

In this type of system, the air is supplied by means of a centrifugal fan commonly known as forced draft (FD) fan. It provides for high air velocity, better air fuel mixing, and smaller burners. The stack is still required to create a negative draft inside the furnace.

Induced Draft

When the height of the stack is inadequate to meet the draft requirements, an induced draft (ID) fan is provided to draw the flue gases out of the heater. Negative pressure inside the furnace ensures air supply to the burners from the atmosphere.

Balanced Draft

When both forced draft and induced draft fans are used with the heater, it is known as a balanced draft system. Most air preheating installation is balance draft.

Based on mounting:

Wall mounted

Floor mounted

Roof mounted

Based on burner:

Single fired burner : Only one fuel either gas or liquid isused.

Double fired burner : Both fuels are used simultaneoulsly.

In ccr double fired is used.

Based on construction:

Typical problems observed in fired heaters include:

1. High excess air operation

2. Fouled convection sections

3. High stack temperature

First one is used in continuous catalytic

Dual fired

4. Over-firing

5. Bad flames/flame impingement

Examples of some of the problems are:

1. Operating heat duty—90 MM Btu/hr (Designed for 50 MMBtu/hr)

2. Excess air—40% (Designed for 15%)

3. Stack flue gas temperature—700°F (Designed for 530°F)

4. Radiant tube metal temperature—830°F (Designed for 450°F)

5. Burner flame lengths—20–25 ft. (Designed for 12 ft.)

Fired Heater Controls Process Side

Fluid being heated inside the tubes needs to be controlled for efficient heat transfer and to minimize fouling and coking of the tubes.

Flow distribution at inlet is very important. All fluid passes should have an equal amount of fluid passing through the tubes. In most of the liquid or fouling services, it is important to have an individual pass flow controller to avoid unbalancing of the flow due to coking or localized overheating. Scheme is shown below :

Fluid flowing in the tubes should have an adequate pressure drop in the fired heater to ensure good distribution of the fluid in a multiple-pass heater.

If the pressure drop across the heater is low, then there is a chance for flow imbalance and the pass may run dry.

Flow regime and coil velocities at the outlet in vaporizing services needs to be watched. If the tube experiences slug flow or very high velocities, then there could be a problem and the tubes will start to vibrate or they can have erosion failure.

Firing Controls:

Three major parameters that need to be controlled and monitored are:

1. Fuel gas/Fuel oil pressure

2. Excess air and

3. Draft in the furnace

Fuel Pressure

One of the simplest schemes for the control of fuel pressure is shown in above figure. The feed output temperature controller provides the set point for the burner fuel pressure controller.

Sometimes the feed outlet temperature is directly connected to the fuel control valve.

If the heater is fired with more than one fuel, then one of the fuels is base loaded and set at a constant firing rate while the second fuel under control takes load fluctuations.

Excess Air Control :

Excess air control essentially involves answering three basic questions:

1. How much excess air is provided?

2. How much excess air should be provided?

3. How efficient is the burning equipment?

Flue gas analysis provides the answer to the first question.

The oxygen concentration in the flue gas provides an indication of the excess air supplied to the combustion process. Above graph shows the relationship between oxygen content and the excess air for a typical fuel gas.

Optimum excess air is the minimum excess air because it minimizes the heat loss to the flue gases, minimizes the cooling effect on the flame, and improves the heat transfer.

With less than the minimum excess air, the unburned fuel will start appearing in the flue gas due to insufficient air.

Draft control scheme:

Control schemes have been installed in the balanced draft systems to control the excess air and draft more accurately. Some of these schemes involve control of the air/fuel ratio. Several problems have been experienced in measuring the fuel and air flow rate accurately.

Balanced draft

Control

In the case of the fuel, the fuel gas quality (composition) keeps on changing in the refinery. For liquid fuels, the fuel viscosity is so high and temperature dependent that a reliable flow measurement over a period of time is very difficult to obtain.

Combustion air flow rate is also difficult to measure reliably, as straight run-lengths for the installation of instruments are not available except when a venturimeter is installed in the suction stack of the FD fan.

A control scheme is shown above

Operating conditions of reformer furnace:

Fuel gas inlet temperature in furnace – 312 k

Fuel gas inlet pressure – 1atm

Stack temperature – 510k

% O2 in flue gas – 4.42%

Fuel gas composition:

Components % volumeHydrogen 29.95%Hydrogen sulfide NillOxygen 0.40%Nitrogen 9.61%Methane 24.78%Ethane 16.44%Propane 3.54%Iso-butane 0.87%Propene 2.36%n-Butane 0.55%Iso butane 0.05%n-pentane 0.08%Iso pentane 0.16%Hexane 0.18%

Calculation of efficiency :

Efficiency = Heat absorbed * 100

Heat supplied

= ( 1 - Heat taken by flue gases from stack ) * 100

Heat given by fuel gases

BASIS – 100 ft 3 /hr of fuel gas is passed through furnace .

Calculation of heat given by fuel gases:

Sample calculation:

For hydrogen = 29.95% = 29.95 ft3/hr

Heat of combustion of hydrogen = 325 Btu/ft3

Heat given by combustion of hydrogen = 29.95 * 325 = 9616.7 Btu/hr

Calculation:

Components Volume flow rate ft3/hr

Heat of combustion @

Btu/ft3Heat given / Btu

Hydrogen 29.95 325 9616.75Hydrogen sulfide Nill - -Methane 24.78 1013 25102.14

Ethane 16.44 1792 29460.48Propane 3.54 2590 9168.6Propene 2.36 2336 5512.96Iso butane 0.87 3363 2925.81n-butane 0.55 3370 1853.5Iso butane 0.05 3068 153.4n-pentane 0.08 4016 321.28Iso pentane 0.16 4008 641.28Hexane 0.18 4762 857.16Oxygen 0.40 - -Nitrogen 9.61 - -

Total 85613.36

Net heat of combustion is 85613.36 Btu/hr. which is equal to = 85613.36 * 1.055 KJ/hr

=90322.0948 KJ/hr

@ Datas taken from Perry’s handbook of chemical engineering

Calculation of heat losses taken away by flue gases from stack :

Basis : 20% excess air is passed

Assumption :

1. complete combustion hence CO is not there in flue gas.2. SOx and NOx are neglection in flue gases.

Flue products:

Components of Fuel gas

Volumetric flow rate ft3/hr

CO2Ft3/hr

H2OFt/hr

N2 Ft3/hr

Hydrogen 29.95 - 29.95 56.306Methane 24.78 24.78 49.56 186.5934Ethane 16.44 32.88 50.64 216.68Propane 3.54 10.62 14.16 66.6228Propene 2.36 7.08 9.44 39.9784Iso butane 0.87 3.48 4.35 21.254n-butane 0.55 2.2 2.75 13.4585Iso butane 0.05 0.2 0.2 1.1295n-pentane 0.08 0.4 0.24 2.4088Iso pentane 0.16 0.8 0.96 4.8176Hexane 0.18 1.08 1.26 6.4368

Total 83.52 164.43 615.6909

Air required for combustion = 615.6909/0.7809 = 788.435 ft3/hr

Total CO2 in flue gas after combustion = CO2 in air + CO2 coming from combustion

= 0.03 * 788.435 + 83.52

= 107.173 ft3/hr

Total O2 in flue gas = 0.21 * 157.687 = 33.1128 ft3/hr

Total N2 coming in flue gas = 615.6909 + 0.79 * 157.687 (coming from excess air ) = 750.25 ft3/hr

Calculation of heat car ried by flue gas when exit from stack:

Stack outlet temperature – 512 k

Stack outlet pressure – 1 atm

Sample calculation :

Total nitrogen in flue gas – 750.25 ft3/hr

Density of nitrogen at 512 k - .042036 lb/ft3

Molar flow rate from stack – 2.476 kmol/hr

Heat taken = n R 300∫512 (A+BT+CT2+DT-2) dT

= n R{ 210A + 85050 B + C 35217000+ 0.0013725 D)

Calculation :

Components of flue gas

Flow rate ft3/hr

Density Lb/ft3

NKmol

A B103

C106

D10-5

QKJ/hr

Nitrogen 750.25 0.042036 2.476 3.280 0.593 - 0.04 15342.74

Carbon dioxide

107.173 0.066 0.3536 5.457 1.045 - -1.157

3163.4

Water 164.43 0.0269 0.5406 3.470 1.450 - 0.121 3904.00

Oxygen 33.1128 0.0478 0.1088 3.639 0.506 - -0.227 702

Total 23112.192

EFFICIENCY = (1 – HEAT LOST IN FLUE GASES / HEAT GIVEN BY FUEL GASES)

= (1- 23112.192/90322.09) * 100

= 74.41%

OPTIMIZATION OF FURNACE :Comparison of %excess air with efficiency :

Stack temperature : 512 k

Fuel gas passed : 100 ft3/hr

% Excess air % Efficiency10 76.43015 75.53520 74.41025 73.72430 72.837

1. According to this table it can be easily seen that keeping the feed rate of fuel gas on decreasing the excess air there is an increase in efficiency.

2. This graph is showing that approximately linearly %efficiency is decreasing with increase in excess air.

3. On the contrary if we are operating furnace at the same efficiency then even 1% reduction in excess air will reduce the FUEL GAS consumption for providing the same amount of heat.

4. Now excess air can’t be reduced to a level which can lead to incomplete combustion of fuel gas.5. 10-15 % excess air can be assumed the optimized level at which heater can be operated

considering all the factors.

Analysis:

IN THE PICTURE GIVEN ABOVE THE FURNACE USED TO HEAT

THE NAPTHA COMING FROM REACTOR IS SHOWN

There are four feed furnaces operating simultaneously having common

convection section and stack and different radiant section.

1. Considering one heater’s radiant section:

Heat in = 15 Gcal/hr

Heat absorbed in radiant section = 9.24 Gcal/hr

Efficiency of radiant section = ( 9.24/15.64) * 100 = 59.079 %

2. Since one radiant section is operating at such low efficiency, hence to recover the heat lost WHB is there in convection section containing economizer and steam generator and naptha is also heated.

Datas taken

from manual

3. Efficiency 75% which is coming in the above calculation is based on the heat absorbed in radiant section + waste heat boiler compete.

CONCLUSION:

FROM THE ABOVE CALCULATIONS AND THEORY IT IS CONCLUDED THAT IT WILL BE SAFE AND ECONOMICAL TO OPERATE THE REFORMER FURNACE BETWEEN 13 TO 17 % EXCESS AIR.

AS LESS EXCESS AIR CAN RESULT IN INCOMPLETE COMBUSTION WHICH WILL CAUSE WASTAGE OF FUEL, ALSO HAZARDOUS TO ENVIRONMENT AND MORE EXCESS AIR WILL LEAD TO EXTRA HEAT LOSS, MORE AMOUNT OF FUEL HAD TO BE BURNT TO GET THE SAME EFFICIENCY.