1 Introduction
High-intensity gas discharge lamp (HID) is the third generation light source after incandescent lamp and fluorescent lamp, and is a revolution in the history of electric light source development. HID greatly improves the light efficiency of the light source, and the power range is also significantly expanded. For decades, various HID sources such as high pressure mercury lamps, high pressure sodium lamps, and metal halide lamps have made great progress.
HID light sources are inseparable from the use of mercury, or modern light sources including high-pressure mercury lamps, high-pressure sodium lamps, metal halide lamps, and even ultra-high pressure mercury lamps, all of which are outstanding effects of mercury vapor. As people's awareness of mercury hazards has increased, questions have been raised about the use of HID light sources. And led to a series of related questions: how to comprehensively evaluate the mercury in HID light source? What is the acceptable mercury content of mercury-containing lamps from an environmental perspective? How to evaluate mercury-free HID light source?
These problems have caused great repercussions in the society and even in the industry. Some scholars have no mercury in the lamp as the primary indicator of green light source, regardless of light efficiency and longevity. Some authoritative departments even want to introduce measures to limit mercury-containing light sources. To this end, this paper analyzes the HID source and its mercury content as follows.
2. Source of mercury in HID source
Mercury in the polluted environment comes from two aspects, one is of course the consumption of lamps and the mercury in the lamps when the lamps are discarded. Another source that is not recognized by the public is the power consumption of the coal-fired fuel in the coal-fired power plants. in. The total amount of mercury that causes environmental pollution during the entire life of the electric light source is the sum of the two.
In order to quantitatively analyze the main sources of mercury pollution in the lamp, we must first calculate the amount of mercury per 1 kWh of electricity consumed by the electric light source, and the amount of mercury in the power plant depends on the amount of mercury in each kilogram of coal, 1 kWh per lamp. The amount of coal consumed and the proportion of thermal power generation (basically, there is no mercury emission in non-thermal power generation).
Mercury is an associated impurity in coal. The mercury content of various coals is not the same. The content is usually 0.096~2.67ppm, and the comprehensive value is 0.55ppm, that is, 0.55mg mercury is emitted per 1kg of coal. atmosphere.
The coal consumption of thermal power generation is 0.337kg/kWh standard coal (600MW unit) to 0.406kg/kWh standard coal (100MW unit), and the average standard coal consumption is 0.375kg/kWh.
At present, the proportion of China's thermal power generation to total power generation is 73.7%, (hydraulics account for 24.55%, others account for 1.75%), and the product of these three is: c=0.55×0.375× 73.7% = 0.152 mg / kWh.
Of course there are different values ​​in different countries. This value is declining as power generation technology advances and the proportion of coal-fired power plants decreases. In order to be able to compare different types of light sources, we introduce a parameter M, which indicates the total amount of mercury released by a lamp in a unit of time. The author uses the number of milligrams of mercury released per thousand lumens per thousand hours, called the total mercury release. Total mercury release formula: M=H/LT+c/e where: H—the amount of mercury contained in the lamp; L—the average total luminous flux (kLm) during the lifetime of the source; T—the lifetime of the light source (kh); c— The amount of mercury emitted to the atmosphere by each 1kWh electric power plant is 0.152mg/kWh; e-light source one of the most basic parameters "lighting efficiency" (Lm/W).
3, different types of HID have different total mercury release
We calculated the mercury release degrees of different lamps (including mercury-free incandescent lamps and fluorescent lamps as reference), and the results are shown in the table below.
4, high-power long-life HID lamp can be approximated as a mercury-free light source
In the total mercury release formula, when H/LT <<c/e, the lamp can be approximated as a mercury-free light source, so that the condition of the "mercury-free light source" is H<<cpT. As long as the power p of the lamp is sufficiently large and the lifetime T is sufficiently long, this condition can always be satisfied. For any HID source with a power of 250W and a lifetime of 12000h, cpT = 500mg, the lamp contains less than 50mg of mercury, which is an order of magnitude lower than it, negligible.
At this time, the total amount of mercury released is M=c/e, so the high-power long-life HID lamp can be regarded as a mercury-free light source. Its primary environmental protection goal is not to reduce the mercury in the lamp, but to improve the luminous efficiency. It can be clearly seen from the far right column in the above table: (1) The total mercury pollution in the environment cannot only look at the mercury content in the lamp. The mercury-free incandescent lamp is actually higher than the mercury contamination of any light source; (2) Compared with mercury pollution of fluorescent lamps (including compact fluorescent lamps), standard high-pressure mercury lamps are comparable, while high-pressure sodium lamps and metal halide lamps are much better; (3) in HID, self-ballasted high-pressure mercury lamps have the highest mercury pollution; (4) In general, HID has the lowest total mercury pollution in the environment.
5. How can the efficacy of mercury-free light source be evaluated for new mercury-free HID sources?
First of all, mercury-free light sources should represent a development direction of HID light sources, especially low-power HID lamps. A truly meaningful mercury-free light source must achieve a certain luminous efficacy. Above we calculated the total mercury release of each lamp, and the total mercury release of the corresponding mercury-free lamp should not be at least higher than this value. According to M=H/LT+c/e, when H=0, the formula becomes M=c/e, which gives the lowest light effect that the mercury-free lamp should achieve: e=c/M For mercury-free high-pressure sodium lamps, e=0 .152/0.0016=95 Lm/W; for mercury-free metal halide lamps, e=0.152/0.0023=66 Lm/W. However, some of the commercially available mercury-free high-pressure sodium lamps on the market, which are self-sealing green HID lamps, have a luminous efficacy of less than 80 Lm/W.
6. Recovery of mercury-containing HID lamps
The use of HID lamps has been expanding continuously, extending from outdoor lighting to indoor lighting and automotive lighting. As a result, production has grown at an extremely fast rate. By 2005, China's annual output has exceeded 100 million. Since the absolute amount of mercury used in each lamp is still relatively high, it is very beneficial to environmental protection if the mercury in the mercury-containing HID source at the end of life can be recovered. In fact, regarding the recovery of mercury-containing waste HID light source, the world has more mature process equipment, and its principle is nothing more than high temperature evaporation, filtration collection and water shock precipitation collection.
Mercury recovery is close to 100%, and the recovery of separated glass and metals is still of value. For the HID of a double-layer bulb, since the mercury in the lamp is only present in the discharge tube, the principle of the recovery device is not so complicated. The recovery of glass, which accounts for more than 60% of the total weight, can be as high as 95%. However, at present, there is no HID company in China that has set up a recycling line for waste HID light source, which is related to the high cost of recycling and the lack of legal constraints. From the experience of foreign countries, a more reasonable solution is to use the economic lever to make the recycling of waste HID light source an independent industry under the guidance of the government.
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