TANWAT POWER PLANT
(case study)
Rabiel Ulomi
Power station Manager
2. BACKGROUND
2.1 Establishment of Tanwat:
Tanganyika wattle company (Tanwat) derives its name from the wattle tree
(acacia mearnsii) from which a form of tannin known as mimosa extract
used in leather industry is processed.
The company was founded in 1949 by Commonwealth Development
Corporation (CDC) by gradual establishment of over 15,000 hectors of
sustainable forest . Only bark which makes up about 20% of the bulk is
processed leaving behind the rest as waste.
2.2 Core business.
Tannin continued to be Tanwat’s major revenue source until late 1960’s
when decline in demand for leather goods brought about by availability of
cheaper synthetic alternatives resulted in initiatives to explore for new
forest products for long term future prospects.
2.3 Diversification
• Years 1970 – 1980’s explore new global business
opportunities.
• Arable crop farming
• Tea business
• Power business
THE PLANT
3.2 Description of major equipments
3.2.1 Boilers (2units)
(1Unit)
Make: Titan towler, Made by Mechmar of Malaysia
German
Type: Water tube
Rated output::15 tonnes per hr each
300X650L-6WT
Operating pressure: 30 bars
Steam temperature : 330 deg c
3.2.2 Steam turbine
Make: Dresser Rand, USA
Type :Condensing Terry turbine
Capacity: 2500kw
Rotor : speed 5345 RPM
3.2.3 Chipping Plant
Make: Klockner,
Type : Drum chipper
Model:KTH
3.2.4 Generator
Make :
AVK , Germany
Rated Cap: 3125 Kva
Rated Terminal V: 3300 v
Rated frequency : 50 Hertz
4.2 PROCESS
4.2.1 FUEL -De-barked wattle logs (acacia mearnsii), Eucalyptas
logs and saw mill wastes are chipped into small size 25 X 25
mm and conveyed to silos for storage from which they are fed
into boiler furnaces at a rate proportional to energy requirement
at the material time.
4.2.2 STEAM- Raw water which is only used as make up is
passed through a cat-ion exchange water softener and comes
out as soft water. It is mixed with condensate before being
pump to thermal deaerator and finally into the boilers. Steam
coming out is superheated steam at a temperature between
300- 3300C. Part of the steam is directed to the prime mover, a
condensing turbine for power generation and the rest is
desuperheated for using in the bark processing plant and sawn
timber dry kiln.
5 PLANT MAINTENANCE
5.1 Preventive maintenance
Direct
Indirect/condition monitoring
-Cleaning
-temperature measurement
-Lubrication,
-vibration tests
-Programmed
-abnormal sound
replacement/overhaul
5.2 Planned shut down maintenance
-Done once or twice a year mainly with the purpose of cleaning
cooling and feed water systems or do major replacement on
chipping plant/conveying system and turbo alternator lubricating
system.
-The maintenance is usually carried out for a period of less
than 12 hrs
-The customers are issued with a one week notice.
Safety
• Developed safety procedures and well
defined activity procedures.
• RIAR- a performance target for staff.
5.3 Annual legal inspection
• The inspection is carried out on boilers, high
pressure vessels, and lifting tackles.
• Boiler inspection involves, physical inspection,
hydraulic test and steam test.
• Pressure vessels inspection involves wall
thickness measurements and relieve valves
testing.
•
• The inspection is done by authorized
Government inspector.
ENERGY DISTRIBUTION
6.1Steam distribution
6.2 Power distribution.
• Tanesco interconnector- through 2000kva,
3300/33000 V transformer
• Power station own consumption-through
1000kva 3300/415V transformer
• Wattle factory/sawmill supply-through 1000kva
3300/415v transformer.
• Kibena tea factory supply-through 2000kva
3300/11000V transformer.
7. CHALLENGES
7.1 Pollution of environment with boiler grits.
Solution: installed a grit arrestor on the flue gas line.
7.2 Monitoring boiler operating parameters
1) Boiler water level-lost one boiler in 1996 due loss of water
Solution: Intensive training on boiler emergency shut down
procedure.
2) Steam temperature control-due lack of attemperator to stabilize
super heated steam temperature.
Solution:1) Training on how reduce steam temp. manually using
super heater drain valve.
2) An alarm was installed to give a warning once
temperature exceeds 330 deg cent.
7.3 Copping with earth faults and lightning
• Njombe climate favours trees growth. This falls on power lines frequently
especially during rain season causing earth faults and turbine tripping.
Soln. 1) Removal of all the trees close to and leaning towards power lines.
2) Staff trained to do a quick reset before the turbine slows down.
7.4 Breakdown of major equipments and lack of standby units.
-eg chipping plant, turbine, and alternator
Sonl. 1) Emphasis on preventive maintenance.
.
2) Maintaining adequate stocks of spare parts and material.
7.5 Lack of skilled labour
The expansion of primary and secondary education in Tanzania, growing
industrial an mining sectors have created very high demand for technical
personnel in the recent past.
Soln.1) Intensive in house training and promotions
2) Improved remuneration package
4. PLANT OPERATIONS
4.1 Organization Structure
Power Station Manager
Senior Engineer
Shift Engineer 4
Boiler Technician-4
Turbine Technician -4
Electrical Techchnician-4
Boiler operator -4
Boiler assistants- 4
Chipper Operator -4
Chipper Attendant - 8
General staff -3
ACHIEVEMENT
•
•
•
•
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Smooth operation for almost 14 yrs.
Experience & Knowledge.
High availability.
Cheap and reliable power source.
Better resource utilization.
Positive contribution towards reduction of
environmental pollution.
FUTURE
(bright)
• The Government of Tanzania encouraging
producers through small power purchase
agreement.
• Availability of biomass
• Tanwat plan to install a 5 Mw plant soon and a
15 Mw plant in the near future.
• Kyoto protocol-carbon credits.