COMPANY PROFILE
2014
Reinstein
49 6898 9030 467 | www.reinstein-energy.com
technical feature
Efficiency Improvement of an industrial power plant in the pulp and paper industry Optimisation of the Industrial Power Plant of a Pulp & Paper Mill In paper manufacture, energy is the decisive production factor. Where a considerable amount of energy in the form of steam and power is consumed, this must be provided as efficiently and cost-effectively as possible. A reason why many enterprises in the pulp and paper industry already opt for their own power plants operating in combined heat and power mode (CHP). However, the power plants often do not work at the efficiency level they could achieve with optimised parameters. The following article presents a feasibility study conducted to identify potential areas of energy efficiency improvement in the pulp and paper mill’s in-house power plant, and its implementation. The project was carried out for the pulp & paper mill Kartonfabrik Buchmann GmbH by the specialised power engineering specialists of Reinstein GmbH.
Although the energy input for the production of one ton of paper has been reduced by more than half in the past 50 years, and meanwhile only 3 066 kWh/t are consumed in the form of steam and electric powerš, paper manufacturers still face great challenges with regard to energy efficiency. According to industry figures, the mean share of energy costs in total production costs is approximately 12%. Energy is a decisive production factor, and the constantly increasing expenditure on this resource presents a permanent threat to the economic efficiency and existence of enterprises. (Fig. 1).
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Energieeinsatz pro Tonne Papier
energy demand per ton of paper
Quelle:
Source:
VOP Verband Deutscher Papierfabriken e.V.
VOP Verband Deutscher Papierfabriken e.V. [German Pulp and Paper Association]
Fig. 1: Energy demand in paper production The pulp & paper industry is one of the most resource intensive basic industries. To counteract increasing costs for electric power and fuel such as oil and gas, manufacturers have already taken a range of energy efficiency enhancement measures:
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optimisations of the production process itself have been implemented, e.g. more efficient components and procedures, renewal of systems or components 72% of the companies utilise the combined heat and power principle in their own power and process steam generation² the kind of fuels used has often been converted to regenerative and environmentally-friendly alternatives; for example, the waste materials created in the production process are being used for energy generation.
However, investigations show that there is certainly still considerable room for further improvement. More efficiency enhancement potentials exist throughout the entire process chain.
1. The initial situation The pulp & paper mill Kartonfabrik Buchmann GmbH situated in Annweiler, Germany, ranges among the leading manufacturers of cartonboard fabricated from recovered paper and fresh fibres. The board machines produce about 240 000 tonnes of cartonboard per year. Buchmann employs 325 people and focuses on environmental protection and sustainability. Processes and systems are consequently advanced and optimised in order to protect resources and minimise emission. For this purpose, Buchmann maintains a consistent energy management system. The company uses the combined heat and power generation method, and the possibilities of heat recovery. Operating around the clock, two natural gas fired power plant units generate the process steam required for the cardboard production (Fig. 2).
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HKW Strom & Wärme Prozessdampfschienen kalte Reserve Kartonfabrik Strom öffentliches Netz
CHP Unit power & heat process steam headers cold standby pulp & paper mill power public network
Fig. 2: Plant layout of Buchmann Pulp & Paper Mill Simultaneously, gas turbines and steam turbines generate a major part of the required electrical energy of up to 15MW. Therefore, only a minor portion has to be obtained from the public network. A standby unit is available for primary steam generation in case of emergency. A detailed review of the facility - which covered exclusively the power plant sector and not the cardboard production itself - was to be conducted to identify potential areas of energy efficiency improvements, which were to achieve the following main goals:
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increasing the mill’s own power generation capacity (reduction or elimination of external energy demand) further reduction of thermal loss fuel savings through improved fuel utilisation changing from water cooling to environmentally-friendly air cooling reliability enhancement and improved incidence control improved recording of operation parameters and further automation of plant control.
2. Challenge and general procedure Energy consumption in pulp & paper mills is highly complex, and measuring as well as control devices, which are required to identify the consumption of steam and electric energy, are partly missing at the individual consumers. If optimisation potentials are to be recognised and evaluated, all plant components and the production process are to be systematically analysed. This challenge was also faced in the present case. The efficiency enhancement measures were implemented in three consecutive process phases (Fig.3).
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1
Potential Analysis
2
Execution of a Tailored Feasibility Study
3
Implementation of the Efficiency Improvement
Analysis Workshop
on Efficiency Improvement
Measures desired by the Client
Fig. 3: Project implementation based on Reinstein’s three-phase-approach Sections 2 to 4 of this article cover the first two phases, whereas phase 3 is described in Section 5 below. In Phase 1, first the technical and economic project goals were determined in a client workshop. Reinstein’s project team consisted of five engineers of the process engineering, steam turbine, gas turbine, boiler, and electrical, control & instrumentation sectors. Afterwards, a detailed inventory was prepared, which required interviews with the client’s experts and executives involved. Their long-term experience in the plant operation allowed weak points to be quickly identified. In addition to analysing the documentation available, Reinstein collected its own measuring data in order to determine the process steam and electric power demand. Finally, the machinery and components, including steam turbine, boiler, generators, electrical equipment, control & instrumentation systems and water supply system were given close scrutiny. In Phase 2, the enhancement proposals resulting from the analyses and inspections were firmed up. Over a prolonged period of time, a multitude of production conditions and plant operation modes including specific incidences could be reviewed. In the process, basic data for the design of components were determined. For example, material balances and energy balances were assessed by means of heat flow diagrams. Finally, the technical specifications for the proposed improvements could be developed, and budget quotations for the individual work packages obtained. When the budget quotations were available, they were reviewed and evaluated technically and economically. Ultimately, this profitability analysis formed the basis for the client’s investment decision. Four efficiency enhancement scenarios were investigated, and two of them, involving comparatively low investment cost, crystallised as the most economical alternatives.
3. Results of the study The industrial power plant at the Buchmann Pulp & Paper Mill has been designed to operate exclusively in combined heat and power mode, which means that a high fuel utilisation rate, and simultaneously a maximum power-to-heat ratio are to be achieved. In addition, the industrial power plant should be capable of controlling incidences resulting from the cardboard production process (such as a sudden break in the paper web). The weak points identified included:
• • • • •
inadequate development of the combined heat and power generation systems - part of the steam energy is still destroyed in reducing valves instead of being turned to energy in a steam turbine avoidable heat loss at the boilers weak points at the steam generators and excessive steam temperatures that cause inefficiency suboptimal unit configuration and inadequate interaction of components outdated control & instrumentation systems which, moreover, are not of redundant design.
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Combined heat and power generation (CHP) The decisive factor for the profitability of a power plant is the facility’s degree of efficiency. With the heat produced by the combustion of one energy medium, conventional thermal power plants generate exclusively electrical energy and achieve efficiencies of approximately 60%. Power plants utilising the combined heat and power principle (CHP) also use the waste heat for energy generation. This technology allows efficiencies of up to 90% to be achieved, since it utilises electric power and heat energy simultaneously (Fig. 4). The heat generated may, for example, be used as district heating for households, or as process heat for production. Because of the high process steam demand in its production process, the pulp & paper industry is an ideal application for the CHP technology.
Luft
Air
Gas
Gas
Gasturbine Generator Gas-Luft-Gemisch Wird In Turbine Verbrannt Kessel Rauchgas
Gas Turbine Generator Gas-Air Mixture Is Combusted In The Turbine Boiler Flue Gas
Wasser
Water
Wasserdampf
Steam
Dampfturbine
Steam Turbine
Strom
Electric Power
Prozessdampf
Process Steam
Fig. 4: Combined heat and power generation principle Reinstein recommended to its client a package of different measures, part of which could also be implemented independently of each other. These included the use of a new steam turbine, the enhancement of the most important boiler, and the improvement of its efficiency through a considerable temperature reduction of its exhaust gases at the stack. An upgrading of the larger gas turbine by a conversion to low-NOx combustion was planned, which would reduce environmental burdens caused by nitrogen oxides. Minor improvements were made to the water-steam cycle and to the control & instrumentation systems.
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Reinstein The study proved that an optimal configuration of the industrial power plant would be able to increase the mill’s own power generation by up to 2.5MW. The thermal loss, which was already at that stage at a low level, could be further reduced from the current 20% to 10-15% of the fuel input. Moreover, an expansion of the existing control and instrumentation systems would simplify the control, render it more transparent, and facilitate incidence control. In addition, the study showed that reduced fuel costs and a smoother operation of the facility would allow the necessary investment to be already amortised within approximately three to five years. Moreover, financial advantages under the CHP subsidisation programme could be expected.
4. Conclusion regarding Sections 1 to 3 above In in-house power plants of pulp & paper mills - like in other sectors -, a multitude of optimisation measures can already be implemented with experienced and well-trained employees. However, the detailed specialised knowledge and expertise of external consulting engineers allow additional aspects and details to be considered that may be overlooked by internal staff. For the project result, it is of prime importance that, using a dedicated methodology, the know-how of the client’s operating team is first surveyed and recognised, and then the internal and external points of view, and existing and newly recorded data integrated in an overall analysis. With every common step taken within the scope of the feasibility study, increased knowledge was gained by both parties, whereas decision uncertainty was reduced. As a result of the study, the profitability of the investments could be estimated fairly accurately investments which are worthwhile even in facilities that are already operating very economically, as they allow pushing the efficiency limits even higher.
Energy is the decisive factor in paper production; the in-house power generation in Buchmann’s own power plant could be significantly increased.
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“Reinstein’s engineers supported us from the initial feasibility study and fully served our interests as expert consultants. All services were completed on schedule, and even below budget.” Armin Lehmann, Technical Manager at Buchmann GmbH, Annweiler, Germany
5. Summary of technical data established during the analysis and feasibility study stages, and implementation of the efficiency improvement measures desired by the client As stated above, the pulp and paper industry is one of the most resource intensive basic industries. Therefore, a lot of factories have their own industrial power plants (so-called IPPs) that utilise the combined heat and power principle (CHP) and achieve high efficiencies. Efficiency is defined as the ratio of economically utilised energy to the overall energy input. The CHP technology allows efficiencies of up to 90% to be achieved, since it generates electric power by also utilising the waste heat energy for the generation of the process steam required for paper production.
5.1 Summary of Goals In 2010, Reinstein’s engineers were tasked by Buchmann with the implementation of the feasibility study. This was focussed exclusively on the power plant section of the facility and not on the cardboard production itself. The entire energy generation situation was to be thoroughly reviewed with a view to enhancing the efficiency of the in-house energy production. During the study, first the goals of the scheme were defined:
5.1.1 Meeting the process steam demand The structure of the facility is the result of historical development, and it is no longer optimally configured at this stage. The improvement measures were to increase the steam generation reliability. The main task of the improved facility would be the provision of the steam actually required for the two cardboard machines, which may always be subject to considerable fluctuation.
5.1.2 Meeting the power demand The total power requirement of the facility is 15MW. For technical reasons, only 6MW can be obtained from the public network. At the end of the project, the total power required was to be generated locally.
5.1.3 Control of incidences The outdated control and instrumentation systems of the original facility did not always allow optimum management of paper fabrication incidences, for example in case of a sudden break in the paper web. A lot of control functions had to be carried out manually. Buchmann hoped that as a result of the measures taken, interruptions in production caused by disturbances in the electrical power supply would be eliminated. This included an increased automation level, which would also allow an improved recording of operating parameters.
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Reinstein 5.1.4 Environmental protection / sustainability The overall fuel demand - natural gas in this case - was to be reduced and the degree of utilisation to be increased. Another requirement to be fulfilled was the protection of resources through the change from water cooling to environmentally-friendly air cooling.
5.2 Layout of the original facility As stated above, with its two cardboard machines, Buchmann GmbH produces more than 240 000 tons of cardboard per year. The generation of energy in the form of process steam and electric power is provided by a complex industrial power plant, which has been equipped over its more than 100 years of corporate history with five units. Together, these units form the so-called “Annweiler IPP”. The power plant, designed to operate exclusively in combined heat and power mode, partly did no longer meet the latest state of power plant technology (Fig. 5).
Fig. 5: Basic diagram of the original IPP before implementation of the measures
HKW Luft Kessel Dampfturbine Kartonproduktion
Chp Unit Air Boiler Steam Turbine Cardboard Production
Druckreduzierstationen
Pressure Reducing Stations
Stromversorgung Gesamtanlage
Power Supply, Entire Facility
Kartonmaschine Nebenanlagen (Entgaser, Wasseraufbereitung etc.) hier nicht dargestellt
Cardboard Machine Balance Of Plant Items (Such As Degasifier, Water Treatment System, Etc.) Are Not Shown Here.
The individual CHP units consist of the following components (for reasons of presentation, balance of plant and ancillary items such as degasifier, demineralisation system, feedwater tank, etc. are disregarded here ):
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CHP Unit 5 was set up in 1975 and modernised later on. It is the basic unit for the supply of the factory with electric power and steam. The unit, which was initially fired with heavy oil, consists of a power boiler and a steam backpressure turbine, which can achieve a power of up to 6MW with the current process steam demand. In 1997, a 4.5MW gas turbine (topping turbine) was provided upstream of the boiler, which is now fuelled by natural gas. The system generates steam at a pressure of 110bar and a temperature of 530°C. Only this unit is equipped with a well-developed water-steam-cycle; therefore, the overall facility is almost exclusively controlled via this unit (technical control room).
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CHP Unit 3 consists of a 3.6MW gas turbine and downstream heat recovery steam generator, which generate steam at 45bar and 450°C. The live steam generated there at a rate of 8.5t/h is immediately fed via pressure reducing stations to the process steam headers. The unit was modernised in 2007 to the present configuration.
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CHP Unit 4, built in 1967, serves for “cold standby” steam generation in case of emergency. This unit can still be fired with heavy oil; the existing turbine is no longer operational.
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CHP Units 1 and 2 have been shut down and decommissioned.
5.3 Optimisation approaches Initially, the weak points of the overall facility were identified and documented in the study. The following areas turned out to offer the highest potential for efficiency improvements:
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In CHP Unit 5, the arrangement of the superheaters (where the steam is heated further) remained unchanged in the boiler itself when the unit was converted from heavy oil firing to natural gas firing (topping turbine). This gave rise to a very high flue gas temperature at the stack, which caused efficiency loss.
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The CHP system was still inadequately developed; part of the steam energy was still destroyed in reducing valves instead of being turned to electric power in a steam turbine.
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The steam backpressure turbine of CHP Unit 5 operated far below its design values and thus with a low efficiency.
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Since the modernisation of CHP Unit 3 in the year 2007, the downstream generation of condensation energy had not been implemented in this unit. Therefore, the in-house power generation in CHP Units 3 and 5 was not sufficient for operating the factory independently of the public network.
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To achieve a comprehensive integration of all functions required for the operation and monitoring of the power plant, some improvements were found to be necessary. The operation and monitoring of the overall power plant process was found to be rather complicated and only to be managed by experienced staff familiar with the particularities of the systems. Control and instrumentation systems were not designed redundantly as is common practice today. Thus, individual faults causing considerable operational malfunctions were unavoidable.
•
Therefore, the unit configuration and the interaction of components were to be optimised.
5.4 Measures implemented In the report on the results of the feasibility study, a package of different measures was recommended to the client, part of which could also be implemented independently of each other. After completion of the profitability review, Reinstein GmbH was tasked with the implementation. The following measures were implemented (Fig. 6):
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Fig. 6: Basic diagram of the IPP after implementation of the measures
• • •
• • •
In CHP Unit 5, the existing gas turbine was replaced by a module of higher capacity, which now increases the power output by approximately 0.5MW to a maximum of 5.4MW. The new system uses the state-of-the-art low NOx combustion technology, which reduces burdens on the environment caused by nitrogen emission (1). Various measures were taken to increase the efficiency of the boiler in CHP Unit 5; mainly by significantly reducing the exhaust gas temperature at the stack. The arrangement of the superheaters was modified and they were partly replaced (2). The steam turbine of CHP Unit 5 was redesigned to meet the actual steam demand and replaced by a new one (“DT7”, with gearbox, generator, and auxiliary systems). The steam generated in CHP Unit 3 is now also routed to the new steam turbine in CHP Unit 5. The new system supplies process steam to the mill’s 8.5bar header as well as to the 3.4bar header. A “destruction” of steam energy in the reducing valves is now eliminated. These combined measures have increased the power to 11.5MW (3). In order to enhance the reliability of the process steam supply, the boiler of CHP Unit 4 was connected to the components of CHP Unit 3 (45bar system) (4), serving as a standby unit. Hardware and software of a state-of-the-art, computer-aided PLC process control system were installed, which will allow the complete facility to be monitored and controlled in a simple and safe manner. Additional improvements have been made to the water-steam-cycle; approximately 75% of the existing piping systems were renewed, which also contributed to the goal of enhancing the power plant efficiency.
5.5 Conclusion Even for facilities already operating with a high degree of efficiency, investments are worthwhile which further increase the energy efficiency and adjust the technology to the latest state of the art. They provide economic and ecological benefit, especially in resource-intensive sectors such as the pulp and paper industry. For extensive optimisation programs, it is advisable to draw on the knowledge and experience of specialised consulting engineers, who work in close cooperation with the plant owner and elaborate tailored solutions. The combination of the individual measures allowed the pulp and paper mill’s in-house power generation capacity to be increased. Now even excess electricity is produced, which may be sold in the market if this is economically reasonable.
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The thermal loss, which was already low before the measures were implemented, was reduced from approximately 20% to 10 to 15% of the fuel input. The upgrading of the existing control and instrumentation systems enhances the transparency and convenience of the plant control, and allows quicker management of incidences. From an economic perspective, Buchmann’s investments will be amortised by fuel savings and a smoother operation within approximately three to five years. The completion of the project is scheduled for the second half of the year 2014.
About Reinstein Reinstein GmbH are consulting engineers specialised in conventional power plants and renewable energies. Reinstein’s services cover the entire lifecycle - from planning, construction, commissioning and operation up to decommissioning. Reinstein’s team provides consultancy in optimisation, reorganisation and change management and assists you in taking strategic decisions, and throughout their implementation. Since 2012, Managing Director Dr.-Ing. Marc Reinstein is a lecturer in Project Management at the University of Saarbrücken, Germany.
¹ VDP Verband Deutscher Papierfabriken e.V. [German Pulp and Paper Association] ² VDP e.V.
www.reinstein-energy.de
Dr.-Ing. Marc Reinstein
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THE ENERGY OF THE FUTURE. INTELLIGENT SOLUTIONS FOR EVERY FACET OF YOUR ENERGY SUPPLY. There are many ways to generate heat, steam and electricity from the most varied energy carriers. We, Standardkessel Baumgarte, know them – and also find new ones. In this case, experience is our best investment. Thanks to the experience of more than 160 years, we have a unique and wide range of process know-how. No matter whether the supply of high-quality components or the construction of sophisticated complete plants is involved – or whether tailor-made solutions for after-sales services and contracting are in demand - we are the right partner. Therefore it is no wonder that power supply companies, municipalities, municipal utilities and industrial companies rely on our competence.
As a strong group of companies, we are driven by one thing in particular:
Ideas full of energy.
Within the Reinstein optimisation project, Standardkessel Baumgarte Service improved the boiler efficiency and adapted the emission values to the new 13. BImschV (IED 2010/75/EU). Furthermore the steam temperature control was modernised by spray attemperators. Former damages due to flue gas imbalances will be avoided in future by a new superheater design. Our engineers are ready to modernise your boiler too. More information and references available at www.ideas-full-of-energy.com or Phone: +49 203 452 460
STANDARDKESSEL BAUMGARTE - Power plants, plant operation, and services for generating electricity, steam, and heat from residues, primary fuels, waste heat, and biomass.
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