Stockholm Energi is in a unique position to develop fuel efficient Combined Heat and Power, CHP, given full utilization of the Stockholm district heating base. This can be furher improved by linking up district heat systems both within Stockholm itself and with neighbouring municipalities. The district heat turnover of 5,5 TWh includes sales of 250 GWh to neighbouring municipalities. These transactions form part of long-term joint projects aimed at achieving rational district heat supply for the region.
The distribution system in the City of Stockholm is geographically divided into three major networks: the Central Network, the North-Western Network and the Southern Network. The current extent of distict heating in Stockholm is shown on the map (Map of Stockholm's district heat system). The total pipe length of the distribution system is 765 kilometers.
The product is successfully sold on the benefits that it is convenient to the customers, provides reliable deliveries and consideration of the environment. If you look out over the central parts of Stockholm on a cold winter's day, you will notice that virtually all individual chimneys have been put out«. District heating covers more than 90 percent of the heat demand in these parts of the city.
The total emissions from Stockholm Energi of nitrogen oxides have been reduced by half between the years 1988-1994. The emissions of sulphur were reduced by two thirds during the same period and the already low emissions of particles were reduced from 61 to 53 metric tons.
There was a slight rise of total emissions between the years 1993 and 1994. This was due to increased use of fuel-based generating facilities.
Looking at emissions per unit of energy, one finds an almost continuous reduction.
Stockholm Energi's district heating production system is being adapted to more use of biofuels, solar heat stored in seawater and purified sewage water. In addition, an increasing input of hydropower is used for running large heat pumps. All these measures add up to nearly 50 percent of renewables used for the production of district heat.
This steady push for more ecology-cycle orientation has it origin in Stockholm Energi's wish to meet customers' demands. The environment-based demands are growing rapidly. Also, the environmental orientation is an important part of Stockholm Energi's involvemnet in work on the local implementation, in Stockholm, of Agenda 21 - the international action programme for the environment and development, aimed at the 21 st Century.
Regional cooperation on district heating has already proven to be fruitful from economic and environmental points of view. Is is fair to assume a further development in this field.
The production assets makes a total of 3 400 MW thermal energy. The largest amount consists of oil-fired plants of 2 000 MW, mainly used during times of high energy demand. The heat pumps of 420 MW are instead used for base production along with the biofuel-fired plants of 200 MW. The use of the electricity boilers of 530 MW is highly dependent on the price of electricity. The only coal-fired plant has a capacity of 220 MW heat.
The use of cogeneration, that is combined heat and power production, makes a total of 480 MW electricity - that is 20 per cent of Stockholm Energi's power generating assets.
The district heat production is divided between many different plants among which the Värtan plant, situated in the Central Network, is the largest. In the Southern Network the main plants are the Hammarby plant and the Högdalen plant and in the North-Western Network the Hässelby plant is the heat producer. In table I the amount of heat produced during 1994 divided on the largest plants is shown.
Here follows a description of the largest production plants Värtan, Hammarby, Högdalen and Hässelby.
| The total heat production in 1994 divided on production plants | ||
| Plant | Network | Heat (GWh) |
| Värtan | Central | 2 600 |
| Hässelby | North-Western | 1 100 |
| Harrmarby | Southern | 800 |
| Högdalen | Southern | 1 200 |
| Total | 5 700 | |
During the 1960s and 1970s, the Värtan plant was converted from electricity generation to heat production as well. The first permanent district heat plant was completed in 1969. District Heat Plant I was equipped with two 110 MW oil-fired hot water boilers. These are directly linked to the district heating network, which means that the water heated in the boilers is the water which then flows into the network.
Four years later, when District Heat Plant 2 was commissioned in response to the steadily growing demand for district heating within the central parts of Stockholm, a different technique was adopted. District Heat Plant 2 has two oil-fired steam boilers, each with a capacity of 160 MW. The steam from the boilers also drives several steam turbine-powered auxilary units.
Electricity demand went on rising and demand for district heating rose so in 1976 a combined heat and power plant (CHP) was installed. The oil-fired boiler set can produce power or heat or both, as required. The Värtan CHP is an impressive installation in many ways. The steam boiler has no fewer than 16 oil burners, each one of which consumes 4 000 litres of oil in one hour. That amount would last an ordinary Swedish household for a full year. Combustion in the steam boiler is so complete that particle emissions come be low the limits set by the National Environmental Board even without the flue gas purification which the CHP is equipped with.
With the district heating demand still rising by nearly ten per cent anually, another district heating plant was colnissioned in 1979. District Heat Plant 3 consists of a large oil-fired hot water boiler of 175 MW capacity. This boiler is indirectly linked to the district heating system, with a heat exchanger, as is the CHP. Four years later it was time for District Heat Plant 4.
In a bid to reduce the buming of oil and improve Stockholm environment, three eletrical steam boilers of 50 MW each were installed in the summer of 1983. This is one of the worlds largest thermal power stations with electrical boilers.
At the beginning of the 1980s, rising oil prices and the avalability of cheap electricity led to a growth of interest in heat pumps. This lead to the building of the Ropsten District Heating Plant, the world s biggest heat pump installation, with a total capacity of 260 MW. Apart from the advantage of being able to use electricity instead of oil as a fuel, the heat pump system gives us the opportunity of using the thermal energy in large amounts of sea water. The Ropsten District Heating Plant has the capacity to keep the whole of the Central Network system supplied on its own during spring, summer and early autumn. It provides about 60 % of the total energy input for the Central Network.
Environmental consideration played a very important part when Stockholm Energi in the 1980s decided to choose a technology for its future production facilities. In 1987 Stockholm Energi signed a contract for the worlds first PFBC plant. PFBC is short for »Pressurized Fluidized Bed Combustion«. The new coal-fired CHP 6, based on the PFBC-technique, conforms to the strictest environmental stipulations as the same time as it has a high level of efficiency. Together with the heat pumps and electrical boilers, the CHP 6 reduces Stockholm Energi's oil dependency. In the addition of dolomite or limestone during combustion restricts sulphur dioxide emissions to a fraction of those from a coal-fired power plant with no purification. The flue gas cleaning system also consists of particle filters and a deNOx-system.
The Hammarby plant is connected with the Högdalen plant since 1991 in a way that makes it possible for heat to be transferred between the two networks. The heat production of the Högdalen plant is based on household waste. During the summer period, the Högdalen plant has a surplus of waste-based heat which is transferred to the Hammarby plant. During the remainder of the year the economics of the operation can be improved by using the link.
The Högdalen plant has been an incineration facility since 1970. To begin with, the plant only produced electricity. At that time the facility was equipped with two waste-fired boilers of 30 MW each. With the expansion of Stockholm's district heating system, the plant was converted into a combined heat and power station in 1979. By that time an oil-fired boiler of 80 MW and two small boilers of 20 MW were installed. The next enlargement came in 1982, with the installation of an electrical boiler of 24 MW. In 1986 a new 40 MW incinerator was installed.
To meet up with the harsh environmental conditions put on incinerating plants, an advanced flue gas cleaning equipment has been built. It consists of a particle filter, a deSOx-system using the dry method and a deNOx-system using the non-cathalytic system. The waste-fuelled incinerators in Högdalen have the most strict NOx-emission requirements in Sweden.
The Högdalen plant is connected with the Hammarby plant since 1991 in a way that makes it possible for heat to be transferred between the two networks. In the south cooperation with the neighbouring municipalities has developed.
This change of fuels was made possible through a very limited reconstruction of the plant. In addtion, with a modest investment the lifetime of the plant was prolonged considerably and without protests from people living in the vicinity.
The reconstruction of the Hässlby plant also positively affects the Swedish market for biofuels, since such a large plant represents a steady and substantial demand. In order to secure fuel supply for this big heat and power factory, Stockholm Energi has joined forces with sawmill industries north of Stockholm, building a factory for production of wood pellets in Härnösand. Pellets are transported by ships and today it is possible to produce approximately 500 GWh of district heat with biopellets. The aim is to base all of the plant's heat production - 1 200 GWh - on biofuel.
In the north-western district cooperation with the neighbouring municipalities has developed.
Customer demand is very encouraging, partly supported by the extremely hot summer of 1994, when sales started. The targets for the first season's sales were beaten and approximately half of the final capacity of 60 MW was sold. The system will be inaugurated during the Unichal Congress in Stockholm June 12-14, 1995.
Claes Lindroth
The President of Unichal