China has a large amount of coal-fired district heating capacity. Where better to look for technology and assistance in upgrading this plant to more efficient operation, and for building new capacity, than to Denmark? Here, Hamdi Saraç writes on efforts by Danfoss and others to bring modern standards to China’s district heating systems.
China’s target to reduce energy intensity by 20% is well publicised, and one of the steps being taken to achieve this ambitions goal is the redevelopment of much of its district heating/cooling (DHC) capacity. District heating has been encouraged by the Chinese government for several decades and the government’s target has pushed development further in this area. Considering building floor area served by district heating in China has increased significantly in the last 20 years; from 276 million m2 in 1991 to over 1100 million m2 in 2000, and it exceeded 2500 million m2 in 2005, with an annual growth rate of 17%, this is a significant growth area which is currently going strong. This growth in district heating has mainly come from the northern and the northeast regions of China where residential buildings account for about 70% of the total district heating area, and commercial buildings account for about 30%.
As coal is the dominant fuel in China, (it accounts for 70% of China’s energy production) and many combined heat and power plants/district heating and cooling (CHP/DHC) facilities are relatively old, the present efficiency of coal-based plant in China is low, on average just 60-65%. Furthermore, in some cities the heat loss from district heating pipelines (as a result of poor insulation and water loss) can be as high as 20-50%. Both of these inefficiencies have reduced the potential benefits of district heating. As a result of this lack of efficiency in current systems, the Chinese government is promoting an Energy Conservation Retrofit Plan on residential buildings and district heating systems in 15 of the northern provinces. The aim of this programme, launched in 2007-08, is to provide 150 million m2 of new district floor heating area in the region.
Danish technology goes to China
Over a decade ago, the Chinese government approached Finland, Sweden and Denmark in order to consult on DHC technologies and their potential uses. Study tours to Denmark were carried out by government officials in order to learn the ‘Danish way’ of doing district heating. These tours were not only to Danish companies which produce DHC technology, but also to consulting companies and companies who produce, distribute and sell heat.
Since then Danish companies and developers have played an important role in cultivating the Chinese DHC market. The Danish government and the Danish DHC industry have since implemented several new DHC projects as part of a special programme dedicated to the Chinese DHC market in Shizi, Chunhua, Tianjin Miajing, Houma, Xian and Harbin. The latest project has been in Changchun in the JiLin Province.
Benefits for the customer and environment
In 2006, Danfoss District Heating signed a contract with CMC International Tendering Company, as official buyer of Changchun District Heating Company, for DHC technology in the city of Changchuan, Jilin Province. Changchun City has a population of approximately 2.8 million people, and a heating area of more than 80 million m2.
Changchun – a built to site substation with 8 MW of heating capacity and a pH dosing water softener unit
Following a request by the Danish government for a minimum of 50% of content of supplies, goods and resources, Danfoss District Heating produced the 40 substations required for the project in locations close to the Danfoss Group headquarters at Nordborg in Denmark. All substations were shipped to China and installation started in autumn 2007. Finally, acceptance certificates were signed between Danfoss District Heating, CMC International Tendering Company and the end user Changchun Heating Group Limited in December 2008. This ensured heat supply for an area of 6.44 million m2
The project covers two new district heating systems for the Yutan development area, which is situated 15 km from the city centre of Changchun. The total system capacity is 381 MW of heat, of which 169 MW is needed for the northern area and 211 MW for the southern area.
This project has seen the district heating network converted from a constant flow system to a variable flow system, where main booster pumps have been equipped with Danfoss frequency converters. The 40 district heating substations have various capacities ranging from 3-10 MW. All substations can be remotely controlled via the supervisory control and data acquisition (SCADA) system so the actual data can be evaluated and optimum operation of the district heating network and substations ensured. This means heat is supplied according to demand.
The project has resulted in a reduction of CO2 of 10%, amounting to approximately 58 tonnes/year. Further, 320 tonnes SO2/year and 58 tonnes NOx/year will be achieved when the last five substations are installed in 2010.
The project has been found to result in 10% savings of coal, which equate to 28,000 tonnes/year. This means 10% less CO2, SO2 and NOx. The collaboration between the Chinese government and the Danish government and DHC companies has resulted in the transition between older, ineffective coal-burning technologies and efficient, demand-meeting systems. The success of the new projects will be monitored and we will be able to see how the energy savings add up for China’s provinces.
Hamdi Saraç is Project Sales Director with Danfoss, Nordborg, Denmark. He has been responsible for the successful implementation of several internationally-financed projects in China and elsewhere. Email: email@example.com
This article is available on-line. Please visit www.cospp.com
Substation design is critical
Design of district heating substations is vital in new district heating networks. Substations must be compact and functional and also accessible. There are two types of substation which can be chosen to meet these criteria: Build to Site (BTS) and Build on Site (BOS).
BTS substations are prefabricated and customized based on the design specification. Benefits of this type of substation are:
- it is a complete product – designed, tested according to control, flow and heat transfer requirements
- ‘plug and heat’ functionality – pre-fabricated substations (with multi-functional controls) reduce installation time and therefore cost
- compact construction which has been designed for easy access to components
- reduction in the demand for space for the heating installation (boilers, etc) – space, which is often expensive, can be used for other purposes
- control functions optimized according to the design
- serial and automated production ensures a consistently high and stable quality level, as well as cost reductions
- renovation of the heating installation/substation can be made during the winter season, with a minimum interruption of the system
- Pressure Equipment Directive (PED) approval is made before the substation is shipped from the factory
- full warranty given by supplier/producer
- only one service partner for the customer
- complete documentation for all components is supplied together with the substation, including user manuals enabling easy installation and commissioning
- customized substations are pre-fabricated in modules where after arrival on-site it is assembled to one unit.
There is limited benefit of BOS substations but there are also several downsides including:
- the substation cannot be completed before all components from the different suppliers are delivered
- building on-site demands a certain level of qualification
- often more expensive and demands more time (depends on local labour costs)
- the function of the substation cannot be tested in advance
- PED approval of the substation made on-site demands a lot of resources
- the substations built on-site are all unique, which can make service more difficult
- can require longer development/installation time.
Technical benefits to customer and environment
Figure 1. Characteristics of a valve
As discussed, technical design of the substation is absolutely vital for the efficient operation of the entire system. In order to gain the full impact of the benefits, sizing of motorized control valves and differential pressure regulating valves must be done with respect to design data.
When selecting control valves, control capabilities included in the range of motorized control valves are based on a split characteristic, which combines the advantages of linear as well as logarithmic characteristics – see Figure 1.
This means that even the most difficult control requirements in district heating can be met, while still providing instantaneous hot water.
Stable control of the valve is obtained in the critical area near the closing position because of the low slope in the split characteristic in this part of the stroke. The steeper part of the characteristic (large flow), on the other hand, enables fast and stable control.
With a large and complex district heating network, it is a must to control the water flow and obtain an optimum distribution of water within the network. This controlled water flow also means heat is available on demand. The valve enables accurate temperature control and low return temperature in the pipe network. Here, differential pressure control valves are unique devices that provide the needed energy. Benefits of differential control are listed in Table 1 on this page.
Differential control valves can easily be mounted in the flow or return line of the entire system. The recommendation is that it is mounted on the return line, which gives lower costs due to low temperature and pressure rating, and longer life time, due to low temperature and pressure.