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ENERGY SAVINGS IN TISSUE PRODUCTION PROCESS: THE CASE OF THE HAYAT TISSUE MILL IN TURKEY.
A. Isiklar, L. Aydin, D. Mainardi and O. Lopez

We are quickly leaving behind us the time when conserving energy in a paper-products mill was a distant ideal to work towards. Instead, we are thrust into a harsh future where energy conservation is as essential as the pulp itself, and the time for talk is over. In this regard, a lot can be learnt from Hayat's Yenikoy Tissue Plant in Turkey, where a cogeneration system has greatly reduced thermal energy costs.

The Yenikoy Tissue Plant was started up in the beginning of 2006, when PMT Italia joined forces with the Hayat Group in Izmit Turkey in order to produce high quality bulk tissue to meet Turkey's growing demand for tissue. Turkey faces similar energy problems to South Africa, and the project called for not just a new mill, but a new more energy efficient mill.

18 months later, the greenfield mill has become the most modern plant of its kind in Turkey. Yenikoy includes a Crescent Former PMT Italia tissue machine for high-quality tissue paper, four unwind stations, and one PMT Italia winding station for the production of multi-layered tissue. The plant also hosts two PMT Italia stock preparation lines, along with the auxiliary systems necessary for the operation of the machine (steam system, high-performance cogeneration hood, lubrication system, DCS, etc.)

The main technical parameters are:

  • Production at converting : 60.000 tpy AD
  • Average daily production: 180 tpd AD
  • Max. daily production: 230 tpd AD
  • Design speed: 2.200 mpm
  • Max. speed: 2.000 mpm
  • Range of basis weights at reel: 14-28 g/m
  • Main tissue products produced: toilet tissue and kitchen towel

MAGIC MACHINERY
What makes the Hayat plant so unique is its machinery, solely designed to optimize the production cycle, the quality of the tissue produced and the energy efficiency. For example, the multilayered headbox (implementing production of soft tissue) has been provided with a dilution system that reduces the 2s value of the basis weight profile, providing fibre savings and optimal winding operation.

The design of the felt run has been carried out with one press solution with the possibility to be easily retrofitted with shoe press; while the large diameter press has been supplied with no driven configuration. The BRUNNSCHWEILER hood is configured so as to use the residual energy in waste gases coming from the two gas turbines installed for production of the electricity needed for the plant. In this way, fuel consumption in the Yankee hood burners is eliminated under normal running conditions.

The exhaust gases coming from the hood are used for the production of the steam needed to feed the YD and the other auxiliary equipment of the mill (wet strength pulper, hall ventilation). The residual energy in exhaust gases in excess from the boiler are used in order to feed a chiller unit, which in turn runs the air conditioning system of the electrical room

THE COGENERATION SYSTEM
The cogeneration process essentially eliminates the inefficiency of drying tissue paper through high temperatures and high drying rates.

The electrical efficiency in Hayat Yenikoy plant is 33.7%, with 66.3% of energy input released as residual heat in the waste gases coming from the turbines. These waste gases have a temperature of approximately 500C and, at high flow rates, can easily be used in a special- design Yankee hoods to reduce and even eliminate the gas consumption in their air. Thermal energy can be utilized this way to dry the tissue, and to generate steam and cold water at a constant temperature. Electrical equipment is needed to distribute the electricity or to produce it in parallel with the utility grid. Hydraulic interconnections are needed to transport cold water or steam wherever it is required.

The cogeneration system in HAYAT Tissue Plant consists of six basic elements:

  • Two 7.5 MW gas turbines, natural gas fired.
  • BRUNNSCHWEILER Yankee Hood.
  • Two steam boilers.
  • Four duct burners (two reserve burners for the hood systems and two reserve burners for the steam boilers, all to be used when the turbines are off).
  • Absorption chillers.
  • New adapted control system in hood air circuits (for the perfect integration between the operation of the hoods and the turbines).

The gas turbine is designed for continuous operation from idle to full load. The turbines feature a lean premix, low emission combustion system for NOx control designed to achieve low NOx and CO.
Grafico-1

Graph 1

Grafico-2
Graph 2

Graph 1 depicts the fluxes of energy in process air of a conventional hood at the same production capacity. Compare this to Graph 2, in which a cogeneration hood is depicted.

Grafico-3
Graph 3

Graph 3 integrates the complete Sankey diagram of the whole process including the gas turbines plant, the Cogeneration hood and the waste heat boilers. The absorption chillers are not shown for the sake of simplicity.

If we compare graphs 1 and 3, we can see that the waste energy flows delivered to the atmosphere are reduced with the complete integration of the three processes (Electricity generation, tissue drying and steam generation), which means that the total energetic efficiency of the system is improved. This improvement with the actual efficiency parameters normally could be computed.

The improvement is much more evident if we consider that the energy that we still deliver to the atmosphere is associated with low-temperature waste gases flow that has a very low quality or capacity to generate work or any other useful effect.

The main advantages of the system are therefore:

  • Better gas energy saving,
  • Minimum gas energy loss through chimney because of use of residual thermal energy from cogeneration gases for drying,

Comparison table: Conventional vs. Cogeneration Hood

Air System

Conventional hood

BRUNNSCHWEILER Cogeneration hood

Type

Duo-cascade

Duo-parallel

Recirculation

80%

0%-20%

Exhaust air flow

20%

80-100%

Exhaust air temperature

200-250C (After heat recovery)

400-420C (No heat recovery)

Exhaust air humidity

400-500 gH2O/kg

100-150 gH2O/kg

Exhaust air thermal power

Low

High

Impingement air flow

Same

Same or lower

Impingement air temp.

510C

510C

Impingement air humidity

200-400 gH2O/kg

50-80 gH2O/kg

Make up air flow

10 %

80-100 %

Make up air temperature

200-280C

450-550C

Make up air humidity

5-10 gH2O/kg

40-50 gH2O/kg

Process temperature

330-380C

450-510C


CALCULATIONS
Yenikoy has two gas turbines, with each one producing 7,315 kW at 15 C (and 97,000 kg/h of waste gases at 490C). In Turkey, electrical energy is more expensive than thermal energy (natural gas, for instance), allowing 3 kW of electrical energy to be produced using 1 Nm/h of natural gas. The rest of the energy is utilised for the steam generation and chilled water production, apart from the use of the waste gases in the BRUNNSCHWEILER Yankee hoods.

CONCLUSION
Desired operation of the cogeneration system as explained before is based on the simplified control of installations which are listed below:

  • Parallel arrangement to simplify controls and enable easy integration between gas turbines and Yankee hoods.
  • Control of available pressure in the turbine exhaust.
  • Control of balance in the hoods.
  • Control of supply temperature.
  • Control of Δp in combustion fans.
  • No reason for moisture control in the exhaust from the Yankee hood.
  • Bypass arrangement.
  • Control of pressure in waste heat boiler.

For the total efficiency point of view, cogeneration type drying is clearly the right choice, and it opens a new field in the use of residual energies in the drying processes where very modest attempts in this respect have been carried out in the past. The main innovation of this project (now, a reality) lies in the fact that no one has ever undertaken an integration to this extent.

For further information please contact davide.mainardi@pmtitalia.com, or contact the PMT South Africa head office. PMT South Africa operates a comprehensive 2500 sq m service facility in Johannesburg.

THE AUTHORS
A. Isiklar (Energy Consultant - Hayat Kimya Tissue Mill- Izmit-Turkey) 
L. Aydin (Mill Manager- Hayat Kimya Tissue Mill- Izmit-Turkey)
D. Mainardi (Product Manager Tissue Lines-PMT Italia S.p.A.- Pinerolo (TO) –Italy)
O. Lopez (R&D Manager-BRUNNSCHWEILER SA- Munguia-Spain)
 

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