12th International Symposium on District Heating and Cooling

The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, Estoniaproduction is quite seasonal following the water flows.The amount of power produced by the Daugava riverHPP cascade is average 2.6–2.8 TWh [1] annually,reaching in the years, rich by spring floods and raineven 4.5 TWh [ [5].equipment with this capacity heat production bycogeneration would be a maximum.More in detail the three HPPs, located on the river ofDaugava, form a sort of cascade with the relativecapacity of: Plavinas 870 MW, Kegums 263 MW andRiga 402 MW.Almost two thirds of hydro electricity is produced in thespring month of March, April and May. In this period thesupplies are from the hydro plants. In the high demandwinter season amount of electricity generated by hydroplants is relatively low.Looking the electricity supply statistics [1] the nationalproduction of electricity is around 10.0 PJ where the9.8 are produced using hydro energy and 0.2 PJproduced by wind energy. The net electricity import(including the amount of energy exported) is around10.8 PJ approximately the 50% of the national supply.These figures shows the lacks of energy sources in thenational system and seems reasonable to foreseen amore large fraction of other energy sources for theproduction of electricity, the main question is on whichmethodology base this strategy .2.2 Well organized and developed DH systemLatvian heating primarily is performed on a centralizedbasis consequently consumers are grouped and theheat is supply from heat source which is established fora certain consumer group. The heat source power,depending on type of consumer group, varies from therange of kW to several hundred of MW. In generallower power can correspond to building groups,individual houses or even apartments heating.Residential and separate heating of individual housesbelongs mainly from the decentralized heating. One ofthe benefits of district heating is centralization of heatload, which gives a possibility to increase the heatsource power and to form basis for the development ofcogeneration power. For large heat consumers inLatvia (mainly heating systems in large cities like Riga)large cogeneration plants are installed. The customerswho are not connected to a district heating cannot beprovided from this system. In the other regions far fromthe big cities the heat supply system is mainly basedon district heating, consequently it means that thatthere possibility for a CHP development.CHP plants cover only a part of the total heat load. Therest of the load is covered by the peak load boilers.This means that following the total heat capacity of thesource, the potential heat capacity of cogenerationshould be assessed quantitatively. Heat capacity ofcogeneration plant has to be selected so that operating179Fig. 3. Heating energy distribution by cities in LatviaIf we are looking at the district heating division of Latviaa huge difference can be seen in quantity of heatsupply in Riga and the rest of Latvia (see fig. 3)Two large CHP plants, Riga TPP-1 with an installedelectric capacity of 144 MW and Riga TPP-2 (390 MW),are located in Riga [5]. CHP plants are the main heatgeneratingsources of heating networks of Latviancapital. Power is produced mainly in cogenerationmode, according to the heat–load curve.During the heating season, when there is a substantialdemand for heating and hot water, Riga CHP plantsproduce approximately 80% of the total annualproduction volume, while during summer the volume ofproduction reduces [5].Nowadays Riga CHP plants cover about 20% of thetotal annual power demand of Latvia [5] .The main fuel used in Latvia biggest cities is naturalgas and the rates of thermal energy are 75% - 85% [3].In Riga and other cities where most part of the heat isproduced in cogeneration cycle, the increase of rateswas not so high and currently (in the autumn of 2009)heat rates are lower that in the cities where wood chipsare used.From the thermal energy point of view seventy percentof the heat in Latvia is supplied from district-heatingsystems either from boiler houses or co-generation:37% of the district heating in Latvia was produced bymeans of co-generation plants [6]. This means that63% of the district heating is produced in boiler houses[6]. This means that there is potential to replace someof the heat plants with co-generation units (Eightypercent of the district heating in Denmark is suppliedfrom CHP [6]).As for heat supply outside of Riga, the dominantthermal energy is produced in boiler houses with